| Message ID | 20191030224930.3990755-6-jhubbard@nvidia.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | mm/gup: track dma-pinned pages: FOLL_PIN, FOLL_LONGTERM | expand |
On Wed, Oct 30, 2019 at 03:49:16PM -0700, John Hubbard wrote: > Introduce pin_user_pages*() variations of get_user_pages*() calls, > and also pin_longterm_pages*() variations. > > These variants all set FOLL_PIN, which is also introduced, and > basically documented. (An upcoming patch provides more extensive > documentation.) The second set (pin_longterm*) also sets > FOLL_LONGTERM: > > pin_user_pages() > pin_user_pages_remote() > pin_user_pages_fast() > > pin_longterm_pages() > pin_longterm_pages_remote() > pin_longterm_pages_fast() > > All pages that are pinned via the above calls, must be unpinned via > put_user_page(). > > The underlying rules are: > > * These are gup-internal flags, so the call sites should not directly > set FOLL_PIN nor FOLL_LONGTERM. That behavior is enforced with > assertions, for the new FOLL_PIN flag. However, for the pre-existing > FOLL_LONGTERM flag, which has some call sites that still directly > set FOLL_LONGTERM, there is no assertion yet. > > * Call sites that want to indicate that they are going to do DirectIO > ("DIO") or something with similar characteristics, should call a > get_user_pages()-like wrapper call that sets FOLL_PIN. These wrappers > will: > * Start with "pin_user_pages" instead of "get_user_pages". That > makes it easy to find and audit the call sites. > * Set FOLL_PIN > > * For pages that are received via FOLL_PIN, those pages must be returned > via put_user_page(). > > Signed-off-by: John Hubbard <jhubbard@nvidia.com> > --- > include/linux/mm.h | 53 ++++++++- > mm/gup.c | 284 +++++++++++++++++++++++++++++++++++++++++---- > 2 files changed, 311 insertions(+), 26 deletions(-) > > diff --git a/include/linux/mm.h b/include/linux/mm.h > index cc292273e6ba..62c838a3e6c7 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -1526,9 +1526,23 @@ long get_user_pages_remote(struct task_struct *tsk, struct mm_struct *mm, > unsigned long start, unsigned long nr_pages, > unsigned int gup_flags, struct page **pages, > struct vm_area_struct **vmas, int *locked); > +long pin_user_pages_remote(struct task_struct *tsk, struct mm_struct *mm, > + unsigned long start, unsigned long nr_pages, > + unsigned int gup_flags, struct page **pages, > + struct vm_area_struct **vmas, int *locked); > +long pin_longterm_pages_remote(struct task_struct *tsk, struct mm_struct *mm, > + unsigned long start, unsigned long nr_pages, > + unsigned int gup_flags, struct page **pages, > + struct vm_area_struct **vmas, int *locked); > long get_user_pages(unsigned long start, unsigned long nr_pages, > unsigned int gup_flags, struct page **pages, > struct vm_area_struct **vmas); > +long pin_user_pages(unsigned long start, unsigned long nr_pages, > + unsigned int gup_flags, struct page **pages, > + struct vm_area_struct **vmas); > +long pin_longterm_pages(unsigned long start, unsigned long nr_pages, > + unsigned int gup_flags, struct page **pages, > + struct vm_area_struct **vmas); > long get_user_pages_locked(unsigned long start, unsigned long nr_pages, > unsigned int gup_flags, struct page **pages, int *locked); > long get_user_pages_unlocked(unsigned long start, unsigned long nr_pages, > @@ -1536,6 +1550,10 @@ long get_user_pages_unlocked(unsigned long start, unsigned long nr_pages, > > int get_user_pages_fast(unsigned long start, int nr_pages, > unsigned int gup_flags, struct page **pages); > +int pin_user_pages_fast(unsigned long start, int nr_pages, > + unsigned int gup_flags, struct page **pages); > +int pin_longterm_pages_fast(unsigned long start, int nr_pages, > + unsigned int gup_flags, struct page **pages); > > int account_locked_vm(struct mm_struct *mm, unsigned long pages, bool inc); > int __account_locked_vm(struct mm_struct *mm, unsigned long pages, bool inc, > @@ -2594,13 +2612,15 @@ struct page *follow_page(struct vm_area_struct *vma, unsigned long address, > #define FOLL_ANON 0x8000 /* don't do file mappings */ > #define FOLL_LONGTERM 0x10000 /* mapping lifetime is indefinite: see below */ > #define FOLL_SPLIT_PMD 0x20000 /* split huge pmd before returning */ > +#define FOLL_PIN 0x40000 /* pages must be released via put_user_page() */ > > /* > - * NOTE on FOLL_LONGTERM: > + * FOLL_PIN and FOLL_LONGTERM may be used in various combinations with each > + * other. Here is what they mean, and how to use them: > * > * FOLL_LONGTERM indicates that the page will be held for an indefinite time > - * period _often_ under userspace control. This is contrasted with > - * iov_iter_get_pages() where usages which are transient. > + * period _often_ under userspace control. This is in contrast to > + * iov_iter_get_pages(), where usages which are transient. > * > * FIXME: For pages which are part of a filesystem, mappings are subject to the > * lifetime enforced by the filesystem and we need guarantees that longterm > @@ -2615,11 +2635,32 @@ struct page *follow_page(struct vm_area_struct *vma, unsigned long address, > * Currently only get_user_pages() and get_user_pages_fast() support this flag > * and calls to get_user_pages_[un]locked are specifically not allowed. This > * is due to an incompatibility with the FS DAX check and > - * FAULT_FLAG_ALLOW_RETRY > + * FAULT_FLAG_ALLOW_RETRY. > * > - * In the CMA case: longterm pins in a CMA region would unnecessarily fragment > - * that region. And so CMA attempts to migrate the page before pinning when > + * In the CMA case: long term pins in a CMA region would unnecessarily fragment > + * that region. And so, CMA attempts to migrate the page before pinning, when > * FOLL_LONGTERM is specified. > + * > + * FOLL_PIN indicates that a special kind of tracking (not just page->_refcount, > + * but an additional pin counting system) will be invoked. This is intended for > + * anything that gets a page reference and then touches page data (for example, > + * Direct IO). This lets the filesystem know that some non-file-system entity is > + * potentially changing the pages' data. In contrast to FOLL_GET (whose pages > + * are released via put_page()), FOLL_PIN pages must be released, ultimately, by > + * a call to put_user_page(). > + * > + * FOLL_PIN is similar to FOLL_GET: both of these pin pages. They use different > + * and separate refcounting mechanisms, however, and that means that each has > + * its own acquire and release mechanisms: > + * > + * FOLL_GET: get_user_pages*() to acquire, and put_page() to release. > + * > + * FOLL_PIN: pin_user_pages*() or pin_longterm_pages*() to acquire, and > + * put_user_pages to release. > + * > + * FOLL_PIN and FOLL_GET are mutually exclusive. You mean the flags are mutually exclusive for any single call, correct? Because my first thought was that you meant that a page which was pin'ed can't be "got". Which I don't think is true or necessary... > + * > + * Please see Documentation/vm/pin_user_pages.rst for more information. NIT: I think we should include this file as part of this patch... > */ > > static inline int vm_fault_to_errno(vm_fault_t vm_fault, int foll_flags) > diff --git a/mm/gup.c b/mm/gup.c > index 8fb0d9cdfaf5..8694bc7b3df3 100644 > --- a/mm/gup.c > +++ b/mm/gup.c > @@ -179,6 +179,10 @@ static struct page *follow_page_pte(struct vm_area_struct *vma, > spinlock_t *ptl; > pte_t *ptep, pte; > > + /* FOLL_GET and FOLL_PIN are mutually exclusive. */ > + if (WARN_ON_ONCE((flags & (FOLL_PIN | FOLL_GET)) == > + (FOLL_PIN | FOLL_GET))) > + return ERR_PTR(-EINVAL); > retry: > if (unlikely(pmd_bad(*pmd))) > return no_page_table(vma, flags); > @@ -790,7 +794,7 @@ static long __get_user_pages(struct task_struct *tsk, struct mm_struct *mm, > > start = untagged_addr(start); > > - VM_BUG_ON(!!pages != !!(gup_flags & FOLL_GET)); > + VM_BUG_ON(!!pages != !!(gup_flags & (FOLL_GET | FOLL_PIN))); > > /* > * If FOLL_FORCE is set then do not force a full fault as the hinting > @@ -1014,7 +1018,16 @@ static __always_inline long __get_user_pages_locked(struct task_struct *tsk, > BUG_ON(*locked != 1); > } > > - if (pages) > + /* > + * FOLL_PIN and FOLL_GET are mutually exclusive. Traditional behavior > + * is to set FOLL_GET if the caller wants pages[] filled in (but has > + * carelessly failed to specify FOLL_GET), so keep doing that, but only > + * for FOLL_GET, not for the newer FOLL_PIN. > + * > + * FOLL_PIN always expects pages to be non-null, but no need to assert > + * that here, as any failures will be obvious enough. > + */ > + if (pages && !(flags & FOLL_PIN)) > flags |= FOLL_GET; > > pages_done = 0; > @@ -1133,6 +1146,12 @@ static __always_inline long __get_user_pages_locked(struct task_struct *tsk, > * is written to, set_page_dirty (or set_page_dirty_lock, as appropriate) must > * be called after the page is finished with, and before put_page is called. > * > + * A note on gup_flags: FOLL_PIN must only be set internally by the > + * pin_user_page*() and pin_longterm_*() APIs, never directly by the caller. > + * That's in order to help avoid mismatches when releasing pages: > + * get_user_pages*() pages must be released via put_page(), while > + * pin_user_pages*() pages must be released via put_user_page(). > + * > * get_user_pages is typically used for fewer-copy IO operations, to get a > * handle on the memory by some means other than accesses via the user virtual > * addresses. The pages may be submitted for DMA to devices or accessed via > @@ -1151,6 +1170,14 @@ long get_user_pages_remote(struct task_struct *tsk, struct mm_struct *mm, > unsigned int gup_flags, struct page **pages, > struct vm_area_struct **vmas, int *locked) > { > + /* > + * As detailed above, FOLL_PIN must only be set internally by the > + * pin_user_page*() and pin_longterm_*() APIs, never directly by the > + * caller, so enforce that with an assertion: > + */ > + if (WARN_ON_ONCE(gup_flags & FOLL_PIN)) > + return -EINVAL; > + > /* > * FIXME: Current FOLL_LONGTERM behavior is incompatible with > * FAULT_FLAG_ALLOW_RETRY because of the FS DAX check requirement on > @@ -1603,11 +1630,25 @@ static __always_inline long __gup_longterm_locked(struct task_struct *tsk, > * and mm being operated on are the current task's and don't allow > * passing of a locked parameter. We also obviously don't pass > * FOLL_REMOTE in here. > + * > + * A note on gup_flags: FOLL_PIN should only be set internally by the > + * pin_user_page*() and pin_longterm_*() APIs, never directly by the caller. > + * That's in order to help avoid mismatches when releasing pages: > + * get_user_pages*() pages must be released via put_page(), while > + * pin_user_pages*() pages must be released via put_user_page(). Rather than put this here should we put it next to the definition of FOLL_PIN? Because now we have this text 2x... :-/ > */ > long get_user_pages(unsigned long start, unsigned long nr_pages, > unsigned int gup_flags, struct page **pages, > struct vm_area_struct **vmas) > { > + /* > + * As detailed above, FOLL_PIN must only be set internally by the > + * pin_user_page*() and pin_longterm_*() APIs, never directly by the > + * caller, so enforce that with an assertion: > + */ > + if (WARN_ON_ONCE(gup_flags & FOLL_PIN)) > + return -EINVAL; > + > return __gup_longterm_locked(current, current->mm, start, nr_pages, > pages, vmas, gup_flags | FOLL_TOUCH); > } > @@ -2366,24 +2407,9 @@ static int __gup_longterm_unlocked(unsigned long start, int nr_pages, > return ret; > } > > -/** > - * get_user_pages_fast() - pin user pages in memory > - * @start: starting user address > - * @nr_pages: number of pages from start to pin > - * @gup_flags: flags modifying pin behaviour > - * @pages: array that receives pointers to the pages pinned. > - * Should be at least nr_pages long. > - * > - * Attempt to pin user pages in memory without taking mm->mmap_sem. > - * If not successful, it will fall back to taking the lock and > - * calling get_user_pages(). > - * > - * Returns number of pages pinned. This may be fewer than the number > - * requested. If nr_pages is 0 or negative, returns 0. If no pages > - * were pinned, returns -errno. > - */ > -int get_user_pages_fast(unsigned long start, int nr_pages, > - unsigned int gup_flags, struct page **pages) > +static int internal_get_user_pages_fast(unsigned long start, int nr_pages, > + unsigned int gup_flags, > + struct page **pages) > { > unsigned long addr, len, end; > int nr = 0, ret = 0; > @@ -2428,4 +2454,222 @@ int get_user_pages_fast(unsigned long start, int nr_pages, > > return ret; > } > + > +/** > + * get_user_pages_fast() - pin user pages in memory > + * @start: starting user address > + * @nr_pages: number of pages from start to pin > + * @gup_flags: flags modifying pin behaviour > + * @pages: array that receives pointers to the pages pinned. > + * Should be at least nr_pages long. > + * > + * Attempt to pin user pages in memory without taking mm->mmap_sem. > + * If not successful, it will fall back to taking the lock and > + * calling get_user_pages(). > + * > + * A note on gup_flags: FOLL_PIN must only be set internally by the > + * pin_user_page*() and pin_longterm_*() APIs, never directly by the caller. > + * That's in order to help avoid mismatches when releasing pages: > + * get_user_pages*() pages must be released via put_page(), while > + * pin_user_pages*() pages must be released via put_user_page(). > + * > + * Returns number of pages pinned. This may be fewer than the number requested. > + * If nr_pages is 0 or negative, returns 0. If no pages were pinned, returns > + * -errno. > + */ > +int get_user_pages_fast(unsigned long start, int nr_pages, > + unsigned int gup_flags, struct page **pages) > +{ > + /* > + * As detailed above, FOLL_PIN must only be set internally by the > + * pin_user_page*() and pin_longterm_*() APIs, never directly by the > + * caller, so enforce that: > + */ > + if (WARN_ON_ONCE(gup_flags & FOLL_PIN)) > + return -EINVAL; > + > + return internal_get_user_pages_fast(start, nr_pages, gup_flags, pages); > +} > EXPORT_SYMBOL_GPL(get_user_pages_fast); > + > +/** > + * pin_user_pages_fast() - pin user pages in memory without taking locks > + * > + * Nearly the same as get_user_pages_fast(), except that FOLL_PIN is set. See > + * get_user_pages_fast() for documentation on the function arguments, because > + * the arguments here are identical. > + * > + * FOLL_PIN means that the pages must be released via put_user_page(). Please > + * see Documentation/vm/pin_user_pages.rst for further details. > + * > + * This is intended for Case 1 (DIO) in Documentation/vm/pin_user_pages.rst. It > + * is NOT intended for Case 2 (RDMA: long-term pins). > + */ > +int pin_user_pages_fast(unsigned long start, int nr_pages, > + unsigned int gup_flags, struct page **pages) > +{ > + /* FOLL_GET and FOLL_PIN are mutually exclusive. */ > + if (WARN_ON_ONCE(gup_flags & FOLL_GET)) > + return -EINVAL; > + > + gup_flags |= FOLL_PIN; > + return internal_get_user_pages_fast(start, nr_pages, gup_flags, pages); > +} > +EXPORT_SYMBOL_GPL(pin_user_pages_fast); > + > +/** > + * pin_longterm_pages_fast() - pin user pages in memory without taking locks > + * > + * Nearly the same as get_user_pages_fast(), except that FOLL_PIN and > + * FOLL_LONGTERM are set. See get_user_pages_fast() for documentation on the > + * function arguments, because the arguments here are identical. > + * > + * FOLL_PIN means that the pages must be released via put_user_page(). Please > + * see Documentation/vm/pin_user_pages.rst for further details. > + * > + * FOLL_LONGTERM means that the pages are being pinned for "long term" use, > + * typically by a non-CPU device, and we cannot be sure that waiting for a > + * pinned page to become unpin will be effective. > + * > + * This is intended for Case 2 (RDMA: long-term pins) of the FOLL_PIN > + * documentation. > + */ > +int pin_longterm_pages_fast(unsigned long start, int nr_pages, > + unsigned int gup_flags, struct page **pages) > +{ > + /* FOLL_GET and FOLL_PIN are mutually exclusive. */ > + if (WARN_ON_ONCE(gup_flags & FOLL_GET)) > + return -EINVAL; > + > + gup_flags |= (FOLL_PIN | FOLL_LONGTERM); > + return internal_get_user_pages_fast(start, nr_pages, gup_flags, pages); > +} > +EXPORT_SYMBOL_GPL(pin_longterm_pages_fast); > + > +/** > + * pin_user_pages_remote() - pin pages for (typically) use by Direct IO, and > + * return the pages to the user. > + * > + * Nearly the same as get_user_pages_remote(), except that FOLL_PIN is set. See > + * get_user_pages_remote() for documentation on the function arguments, because > + * the arguments here are identical. > + * > + * FOLL_PIN means that the pages must be released via put_user_page(). Please > + * see Documentation/vm/pin_user_pages.rst for details. > + * > + * This is intended for Case 1 (DIO) in Documentation/vm/pin_user_pages.rst. It > + * is NOT intended for Case 2 (RDMA: long-term pins). > + */ > +long pin_user_pages_remote(struct task_struct *tsk, struct mm_struct *mm, > + unsigned long start, unsigned long nr_pages, > + unsigned int gup_flags, struct page **pages, > + struct vm_area_struct **vmas, int *locked) > +{ > + /* FOLL_GET and FOLL_PIN are mutually exclusive. */ > + if (WARN_ON_ONCE(gup_flags & FOLL_GET)) > + return -EINVAL; > + > + gup_flags |= FOLL_TOUCH | FOLL_REMOTE | FOLL_PIN; > + > + return __get_user_pages_locked(tsk, mm, start, nr_pages, pages, vmas, > + locked, gup_flags); > +} > +EXPORT_SYMBOL(pin_user_pages_remote); > + > +/** > + * pin_longterm_pages_remote() - pin pages for (typically) use by Direct IO, and > + * return the pages to the user. > + * > + * Nearly the same as get_user_pages_remote(), but note that FOLL_TOUCH is not > + * set, and FOLL_PIN and FOLL_LONGTERM are set. See get_user_pages_remote() for > + * documentation on the function arguments, because the arguments here are > + * identical. > + * > + * FOLL_PIN means that the pages must be released via put_user_page(). Please > + * see Documentation/vm/pin_user_pages.rst for further details. > + * > + * FOLL_LONGTERM means that the pages are being pinned for "long term" use, > + * typically by a non-CPU device, and we cannot be sure that waiting for a > + * pinned page to become unpin will be effective. > + * > + * This is intended for Case 2 (RDMA: long-term pins) in > + * Documentation/vm/pin_user_pages.rst. > + */ > +long pin_longterm_pages_remote(struct task_struct *tsk, struct mm_struct *mm, > + unsigned long start, unsigned long nr_pages, > + unsigned int gup_flags, struct page **pages, > + struct vm_area_struct **vmas, int *locked) > +{ > + /* FOLL_GET and FOLL_PIN are mutually exclusive. */ > + if (WARN_ON_ONCE(gup_flags & FOLL_GET)) > + return -EINVAL; > + > + /* > + * FIXME: as noted in the get_user_pages_remote() implementation, it > + * is not yet possible to safely set FOLL_LONGTERM here. FOLL_LONGTERM > + * needs to be set, but for now the best we can do is a "TODO" item. > + */ Wait? Why can't we set FOLL_LONGTERM here? pin_* are new calls which are not used yet right? You set it in the other new pin_* functions? Ira > + gup_flags |= FOLL_REMOTE | FOLL_PIN; > + > + return __get_user_pages_locked(tsk, mm, start, nr_pages, pages, vmas, > + locked, gup_flags); > +} > +EXPORT_SYMBOL(pin_longterm_pages_remote); > + > +/** > + * pin_user_pages() - pin user pages in memory for use by other devices > + * > + * Nearly the same as get_user_pages(), except that FOLL_TOUCH is not set, and > + * FOLL_PIN is set. > + * > + * FOLL_PIN means that the pages must be released via put_user_page(). Please > + * see Documentation/vm/pin_user_pages.rst for details. > + * > + * This is intended for Case 1 (DIO) in Documentation/vm/pin_user_pages.rst. It > + * is NOT intended for Case 2 (RDMA: long-term pins). > + */ > +long pin_user_pages(unsigned long start, unsigned long nr_pages, > + unsigned int gup_flags, struct page **pages, > + struct vm_area_struct **vmas) > +{ > + /* FOLL_GET and FOLL_PIN are mutually exclusive. */ > + if (WARN_ON_ONCE(gup_flags & FOLL_GET)) > + return -EINVAL; > + > + gup_flags |= FOLL_PIN; > + return __gup_longterm_locked(current, current->mm, start, nr_pages, > + pages, vmas, gup_flags); > +} > +EXPORT_SYMBOL(pin_user_pages); > + > +/** > + * pin_longterm_pages() - pin user pages in memory for long-term use (RDMA, > + * typically) > + * > + * Nearly the same as get_user_pages(), except that FOLL_PIN and FOLL_LONGTERM > + * are set. See get_user_pages_fast() for documentation on the function > + * arguments, because the arguments here are identical. > + * > + * FOLL_PIN means that the pages must be released via put_user_page(). Please > + * see Documentation/vm/pin_user_pages.rst for further details. > + * > + * FOLL_LONGTERM means that the pages are being pinned for "long term" use, > + * typically by a non-CPU device, and we cannot be sure that waiting for a > + * pinned page to become unpin will be effective. > + * > + * This is intended for Case 2 (RDMA: long-term pins) in > + * Documentation/vm/pin_user_pages.rst. > + */ > +long pin_longterm_pages(unsigned long start, unsigned long nr_pages, > + unsigned int gup_flags, struct page **pages, > + struct vm_area_struct **vmas) > +{ > + /* FOLL_GET and FOLL_PIN are mutually exclusive. */ > + if (WARN_ON_ONCE(gup_flags & FOLL_GET)) > + return -EINVAL; > + > + gup_flags |= FOLL_PIN | FOLL_LONGTERM; > + return __gup_longterm_locked(current, current->mm, start, nr_pages, > + pages, vmas, gup_flags); > +} > +EXPORT_SYMBOL(pin_longterm_pages); > -- > 2.23.0 >
On 10/31/19 4:15 PM, Ira Weiny wrote: > On Wed, Oct 30, 2019 at 03:49:16PM -0700, John Hubbard wrote: ... >> + * FOLL_PIN indicates that a special kind of tracking (not just page->_refcount, >> + * but an additional pin counting system) will be invoked. This is intended for >> + * anything that gets a page reference and then touches page data (for example, >> + * Direct IO). This lets the filesystem know that some non-file-system entity is >> + * potentially changing the pages' data. In contrast to FOLL_GET (whose pages >> + * are released via put_page()), FOLL_PIN pages must be released, ultimately, by >> + * a call to put_user_page(). >> + * >> + * FOLL_PIN is similar to FOLL_GET: both of these pin pages. They use different >> + * and separate refcounting mechanisms, however, and that means that each has >> + * its own acquire and release mechanisms: >> + * >> + * FOLL_GET: get_user_pages*() to acquire, and put_page() to release. >> + * >> + * FOLL_PIN: pin_user_pages*() or pin_longterm_pages*() to acquire, and >> + * put_user_pages to release. >> + * >> + * FOLL_PIN and FOLL_GET are mutually exclusive. > > You mean the flags are mutually exclusive for any single call, correct? > Because my first thought was that you meant that a page which was pin'ed can't > be "got". Which I don't think is true or necessary... Yes, you are correct. And yes you can absolutely mix get_user_pages() and pin_user_pages() calls on the same page(s). OK, I'll change the wording to "mutually exclusive for a given function call". > >> + * >> + * Please see Documentation/vm/pin_user_pages.rst for more information. > > NIT: I think we should include this file as part of this patch... heh. I kept hopping back and forth on this, because I've seen other patchsets that often put Documentation/ into its own patch. But you're right, of course: it's not right to refer to items that are not here until a later patch. I'll merge patch 19 into this one, then. ... >> @@ -1603,11 +1630,25 @@ static __always_inline long __gup_longterm_locked(struct task_struct *tsk, >> * and mm being operated on are the current task's and don't allow >> * passing of a locked parameter. We also obviously don't pass >> * FOLL_REMOTE in here. >> + * >> + * A note on gup_flags: FOLL_PIN should only be set internally by the >> + * pin_user_page*() and pin_longterm_*() APIs, never directly by the caller. >> + * That's in order to help avoid mismatches when releasing pages: >> + * get_user_pages*() pages must be released via put_page(), while >> + * pin_user_pages*() pages must be released via put_user_page(). > > Rather than put this here should we put it next to the definition of FOLL_PIN? > Because now we have this text 2x... :-/ > OK, I'll move it up next to FOLL_PIN, and get rid of the 2x places in gup.c ... >> +long pin_longterm_pages_remote(struct task_struct *tsk, struct mm_struct *mm, >> + unsigned long start, unsigned long nr_pages, >> + unsigned int gup_flags, struct page **pages, >> + struct vm_area_struct **vmas, int *locked) >> +{ >> + /* FOLL_GET and FOLL_PIN are mutually exclusive. */ >> + if (WARN_ON_ONCE(gup_flags & FOLL_GET)) >> + return -EINVAL; >> + >> + /* >> + * FIXME: as noted in the get_user_pages_remote() implementation, it >> + * is not yet possible to safely set FOLL_LONGTERM here. FOLL_LONGTERM >> + * needs to be set, but for now the best we can do is a "TODO" item. >> + */ > > Wait? Why can't we set FOLL_LONGTERM here? pin_* are new calls which are not > used yet right? Nope, not quite! See patch #14 ("vfio, mm: pin_longterm_pages (FOLL_PIN) and put_user_page() conversion"), in which I'm converting an existing get_user_pages_remote() caller. > > You set it in the other new pin_* functions? > Yes I did. Because those work already in their gup() counterparts. thanks, John Hubbard NVIDIA
diff --git a/include/linux/mm.h b/include/linux/mm.h index cc292273e6ba..62c838a3e6c7 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -1526,9 +1526,23 @@ long get_user_pages_remote(struct task_struct *tsk, struct mm_struct *mm, unsigned long start, unsigned long nr_pages, unsigned int gup_flags, struct page **pages, struct vm_area_struct **vmas, int *locked); +long pin_user_pages_remote(struct task_struct *tsk, struct mm_struct *mm, + unsigned long start, unsigned long nr_pages, + unsigned int gup_flags, struct page **pages, + struct vm_area_struct **vmas, int *locked); +long pin_longterm_pages_remote(struct task_struct *tsk, struct mm_struct *mm, + unsigned long start, unsigned long nr_pages, + unsigned int gup_flags, struct page **pages, + struct vm_area_struct **vmas, int *locked); long get_user_pages(unsigned long start, unsigned long nr_pages, unsigned int gup_flags, struct page **pages, struct vm_area_struct **vmas); +long pin_user_pages(unsigned long start, unsigned long nr_pages, + unsigned int gup_flags, struct page **pages, + struct vm_area_struct **vmas); +long pin_longterm_pages(unsigned long start, unsigned long nr_pages, + unsigned int gup_flags, struct page **pages, + struct vm_area_struct **vmas); long get_user_pages_locked(unsigned long start, unsigned long nr_pages, unsigned int gup_flags, struct page **pages, int *locked); long get_user_pages_unlocked(unsigned long start, unsigned long nr_pages, @@ -1536,6 +1550,10 @@ long get_user_pages_unlocked(unsigned long start, unsigned long nr_pages, int get_user_pages_fast(unsigned long start, int nr_pages, unsigned int gup_flags, struct page **pages); +int pin_user_pages_fast(unsigned long start, int nr_pages, + unsigned int gup_flags, struct page **pages); +int pin_longterm_pages_fast(unsigned long start, int nr_pages, + unsigned int gup_flags, struct page **pages); int account_locked_vm(struct mm_struct *mm, unsigned long pages, bool inc); int __account_locked_vm(struct mm_struct *mm, unsigned long pages, bool inc, @@ -2594,13 +2612,15 @@ struct page *follow_page(struct vm_area_struct *vma, unsigned long address, #define FOLL_ANON 0x8000 /* don't do file mappings */ #define FOLL_LONGTERM 0x10000 /* mapping lifetime is indefinite: see below */ #define FOLL_SPLIT_PMD 0x20000 /* split huge pmd before returning */ +#define FOLL_PIN 0x40000 /* pages must be released via put_user_page() */ /* - * NOTE on FOLL_LONGTERM: + * FOLL_PIN and FOLL_LONGTERM may be used in various combinations with each + * other. Here is what they mean, and how to use them: * * FOLL_LONGTERM indicates that the page will be held for an indefinite time - * period _often_ under userspace control. This is contrasted with - * iov_iter_get_pages() where usages which are transient. + * period _often_ under userspace control. This is in contrast to + * iov_iter_get_pages(), where usages which are transient. * * FIXME: For pages which are part of a filesystem, mappings are subject to the * lifetime enforced by the filesystem and we need guarantees that longterm @@ -2615,11 +2635,32 @@ struct page *follow_page(struct vm_area_struct *vma, unsigned long address, * Currently only get_user_pages() and get_user_pages_fast() support this flag * and calls to get_user_pages_[un]locked are specifically not allowed. This * is due to an incompatibility with the FS DAX check and - * FAULT_FLAG_ALLOW_RETRY + * FAULT_FLAG_ALLOW_RETRY. * - * In the CMA case: longterm pins in a CMA region would unnecessarily fragment - * that region. And so CMA attempts to migrate the page before pinning when + * In the CMA case: long term pins in a CMA region would unnecessarily fragment + * that region. And so, CMA attempts to migrate the page before pinning, when * FOLL_LONGTERM is specified. + * + * FOLL_PIN indicates that a special kind of tracking (not just page->_refcount, + * but an additional pin counting system) will be invoked. This is intended for + * anything that gets a page reference and then touches page data (for example, + * Direct IO). This lets the filesystem know that some non-file-system entity is + * potentially changing the pages' data. In contrast to FOLL_GET (whose pages + * are released via put_page()), FOLL_PIN pages must be released, ultimately, by + * a call to put_user_page(). + * + * FOLL_PIN is similar to FOLL_GET: both of these pin pages. They use different + * and separate refcounting mechanisms, however, and that means that each has + * its own acquire and release mechanisms: + * + * FOLL_GET: get_user_pages*() to acquire, and put_page() to release. + * + * FOLL_PIN: pin_user_pages*() or pin_longterm_pages*() to acquire, and + * put_user_pages to release. + * + * FOLL_PIN and FOLL_GET are mutually exclusive. + * + * Please see Documentation/vm/pin_user_pages.rst for more information. */ static inline int vm_fault_to_errno(vm_fault_t vm_fault, int foll_flags) diff --git a/mm/gup.c b/mm/gup.c index 8fb0d9cdfaf5..8694bc7b3df3 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -179,6 +179,10 @@ static struct page *follow_page_pte(struct vm_area_struct *vma, spinlock_t *ptl; pte_t *ptep, pte; + /* FOLL_GET and FOLL_PIN are mutually exclusive. */ + if (WARN_ON_ONCE((flags & (FOLL_PIN | FOLL_GET)) == + (FOLL_PIN | FOLL_GET))) + return ERR_PTR(-EINVAL); retry: if (unlikely(pmd_bad(*pmd))) return no_page_table(vma, flags); @@ -790,7 +794,7 @@ static long __get_user_pages(struct task_struct *tsk, struct mm_struct *mm, start = untagged_addr(start); - VM_BUG_ON(!!pages != !!(gup_flags & FOLL_GET)); + VM_BUG_ON(!!pages != !!(gup_flags & (FOLL_GET | FOLL_PIN))); /* * If FOLL_FORCE is set then do not force a full fault as the hinting @@ -1014,7 +1018,16 @@ static __always_inline long __get_user_pages_locked(struct task_struct *tsk, BUG_ON(*locked != 1); } - if (pages) + /* + * FOLL_PIN and FOLL_GET are mutually exclusive. Traditional behavior + * is to set FOLL_GET if the caller wants pages[] filled in (but has + * carelessly failed to specify FOLL_GET), so keep doing that, but only + * for FOLL_GET, not for the newer FOLL_PIN. + * + * FOLL_PIN always expects pages to be non-null, but no need to assert + * that here, as any failures will be obvious enough. + */ + if (pages && !(flags & FOLL_PIN)) flags |= FOLL_GET; pages_done = 0; @@ -1133,6 +1146,12 @@ static __always_inline long __get_user_pages_locked(struct task_struct *tsk, * is written to, set_page_dirty (or set_page_dirty_lock, as appropriate) must * be called after the page is finished with, and before put_page is called. * + * A note on gup_flags: FOLL_PIN must only be set internally by the + * pin_user_page*() and pin_longterm_*() APIs, never directly by the caller. + * That's in order to help avoid mismatches when releasing pages: + * get_user_pages*() pages must be released via put_page(), while + * pin_user_pages*() pages must be released via put_user_page(). + * * get_user_pages is typically used for fewer-copy IO operations, to get a * handle on the memory by some means other than accesses via the user virtual * addresses. The pages may be submitted for DMA to devices or accessed via @@ -1151,6 +1170,14 @@ long get_user_pages_remote(struct task_struct *tsk, struct mm_struct *mm, unsigned int gup_flags, struct page **pages, struct vm_area_struct **vmas, int *locked) { + /* + * As detailed above, FOLL_PIN must only be set internally by the + * pin_user_page*() and pin_longterm_*() APIs, never directly by the + * caller, so enforce that with an assertion: + */ + if (WARN_ON_ONCE(gup_flags & FOLL_PIN)) + return -EINVAL; + /* * FIXME: Current FOLL_LONGTERM behavior is incompatible with * FAULT_FLAG_ALLOW_RETRY because of the FS DAX check requirement on @@ -1603,11 +1630,25 @@ static __always_inline long __gup_longterm_locked(struct task_struct *tsk, * and mm being operated on are the current task's and don't allow * passing of a locked parameter. We also obviously don't pass * FOLL_REMOTE in here. + * + * A note on gup_flags: FOLL_PIN should only be set internally by the + * pin_user_page*() and pin_longterm_*() APIs, never directly by the caller. + * That's in order to help avoid mismatches when releasing pages: + * get_user_pages*() pages must be released via put_page(), while + * pin_user_pages*() pages must be released via put_user_page(). */ long get_user_pages(unsigned long start, unsigned long nr_pages, unsigned int gup_flags, struct page **pages, struct vm_area_struct **vmas) { + /* + * As detailed above, FOLL_PIN must only be set internally by the + * pin_user_page*() and pin_longterm_*() APIs, never directly by the + * caller, so enforce that with an assertion: + */ + if (WARN_ON_ONCE(gup_flags & FOLL_PIN)) + return -EINVAL; + return __gup_longterm_locked(current, current->mm, start, nr_pages, pages, vmas, gup_flags | FOLL_TOUCH); } @@ -2366,24 +2407,9 @@ static int __gup_longterm_unlocked(unsigned long start, int nr_pages, return ret; } -/** - * get_user_pages_fast() - pin user pages in memory - * @start: starting user address - * @nr_pages: number of pages from start to pin - * @gup_flags: flags modifying pin behaviour - * @pages: array that receives pointers to the pages pinned. - * Should be at least nr_pages long. - * - * Attempt to pin user pages in memory without taking mm->mmap_sem. - * If not successful, it will fall back to taking the lock and - * calling get_user_pages(). - * - * Returns number of pages pinned. This may be fewer than the number - * requested. If nr_pages is 0 or negative, returns 0. If no pages - * were pinned, returns -errno. - */ -int get_user_pages_fast(unsigned long start, int nr_pages, - unsigned int gup_flags, struct page **pages) +static int internal_get_user_pages_fast(unsigned long start, int nr_pages, + unsigned int gup_flags, + struct page **pages) { unsigned long addr, len, end; int nr = 0, ret = 0; @@ -2428,4 +2454,222 @@ int get_user_pages_fast(unsigned long start, int nr_pages, return ret; } + +/** + * get_user_pages_fast() - pin user pages in memory + * @start: starting user address + * @nr_pages: number of pages from start to pin + * @gup_flags: flags modifying pin behaviour + * @pages: array that receives pointers to the pages pinned. + * Should be at least nr_pages long. + * + * Attempt to pin user pages in memory without taking mm->mmap_sem. + * If not successful, it will fall back to taking the lock and + * calling get_user_pages(). + * + * A note on gup_flags: FOLL_PIN must only be set internally by the + * pin_user_page*() and pin_longterm_*() APIs, never directly by the caller. + * That's in order to help avoid mismatches when releasing pages: + * get_user_pages*() pages must be released via put_page(), while + * pin_user_pages*() pages must be released via put_user_page(). + * + * Returns number of pages pinned. This may be fewer than the number requested. + * If nr_pages is 0 or negative, returns 0. If no pages were pinned, returns + * -errno. + */ +int get_user_pages_fast(unsigned long start, int nr_pages, + unsigned int gup_flags, struct page **pages) +{ + /* + * As detailed above, FOLL_PIN must only be set internally by the + * pin_user_page*() and pin_longterm_*() APIs, never directly by the + * caller, so enforce that: + */ + if (WARN_ON_ONCE(gup_flags & FOLL_PIN)) + return -EINVAL; + + return internal_get_user_pages_fast(start, nr_pages, gup_flags, pages); +} EXPORT_SYMBOL_GPL(get_user_pages_fast); + +/** + * pin_user_pages_fast() - pin user pages in memory without taking locks + * + * Nearly the same as get_user_pages_fast(), except that FOLL_PIN is set. See + * get_user_pages_fast() for documentation on the function arguments, because + * the arguments here are identical. + * + * FOLL_PIN means that the pages must be released via put_user_page(). Please + * see Documentation/vm/pin_user_pages.rst for further details. + * + * This is intended for Case 1 (DIO) in Documentation/vm/pin_user_pages.rst. It + * is NOT intended for Case 2 (RDMA: long-term pins). + */ +int pin_user_pages_fast(unsigned long start, int nr_pages, + unsigned int gup_flags, struct page **pages) +{ + /* FOLL_GET and FOLL_PIN are mutually exclusive. */ + if (WARN_ON_ONCE(gup_flags & FOLL_GET)) + return -EINVAL; + + gup_flags |= FOLL_PIN; + return internal_get_user_pages_fast(start, nr_pages, gup_flags, pages); +} +EXPORT_SYMBOL_GPL(pin_user_pages_fast); + +/** + * pin_longterm_pages_fast() - pin user pages in memory without taking locks + * + * Nearly the same as get_user_pages_fast(), except that FOLL_PIN and + * FOLL_LONGTERM are set. See get_user_pages_fast() for documentation on the + * function arguments, because the arguments here are identical. + * + * FOLL_PIN means that the pages must be released via put_user_page(). Please + * see Documentation/vm/pin_user_pages.rst for further details. + * + * FOLL_LONGTERM means that the pages are being pinned for "long term" use, + * typically by a non-CPU device, and we cannot be sure that waiting for a + * pinned page to become unpin will be effective. + * + * This is intended for Case 2 (RDMA: long-term pins) of the FOLL_PIN + * documentation. + */ +int pin_longterm_pages_fast(unsigned long start, int nr_pages, + unsigned int gup_flags, struct page **pages) +{ + /* FOLL_GET and FOLL_PIN are mutually exclusive. */ + if (WARN_ON_ONCE(gup_flags & FOLL_GET)) + return -EINVAL; + + gup_flags |= (FOLL_PIN | FOLL_LONGTERM); + return internal_get_user_pages_fast(start, nr_pages, gup_flags, pages); +} +EXPORT_SYMBOL_GPL(pin_longterm_pages_fast); + +/** + * pin_user_pages_remote() - pin pages for (typically) use by Direct IO, and + * return the pages to the user. + * + * Nearly the same as get_user_pages_remote(), except that FOLL_PIN is set. See + * get_user_pages_remote() for documentation on the function arguments, because + * the arguments here are identical. + * + * FOLL_PIN means that the pages must be released via put_user_page(). Please + * see Documentation/vm/pin_user_pages.rst for details. + * + * This is intended for Case 1 (DIO) in Documentation/vm/pin_user_pages.rst. It + * is NOT intended for Case 2 (RDMA: long-term pins). + */ +long pin_user_pages_remote(struct task_struct *tsk, struct mm_struct *mm, + unsigned long start, unsigned long nr_pages, + unsigned int gup_flags, struct page **pages, + struct vm_area_struct **vmas, int *locked) +{ + /* FOLL_GET and FOLL_PIN are mutually exclusive. */ + if (WARN_ON_ONCE(gup_flags & FOLL_GET)) + return -EINVAL; + + gup_flags |= FOLL_TOUCH | FOLL_REMOTE | FOLL_PIN; + + return __get_user_pages_locked(tsk, mm, start, nr_pages, pages, vmas, + locked, gup_flags); +} +EXPORT_SYMBOL(pin_user_pages_remote); + +/** + * pin_longterm_pages_remote() - pin pages for (typically) use by Direct IO, and + * return the pages to the user. + * + * Nearly the same as get_user_pages_remote(), but note that FOLL_TOUCH is not + * set, and FOLL_PIN and FOLL_LONGTERM are set. See get_user_pages_remote() for + * documentation on the function arguments, because the arguments here are + * identical. + * + * FOLL_PIN means that the pages must be released via put_user_page(). Please + * see Documentation/vm/pin_user_pages.rst for further details. + * + * FOLL_LONGTERM means that the pages are being pinned for "long term" use, + * typically by a non-CPU device, and we cannot be sure that waiting for a + * pinned page to become unpin will be effective. + * + * This is intended for Case 2 (RDMA: long-term pins) in + * Documentation/vm/pin_user_pages.rst. + */ +long pin_longterm_pages_remote(struct task_struct *tsk, struct mm_struct *mm, + unsigned long start, unsigned long nr_pages, + unsigned int gup_flags, struct page **pages, + struct vm_area_struct **vmas, int *locked) +{ + /* FOLL_GET and FOLL_PIN are mutually exclusive. */ + if (WARN_ON_ONCE(gup_flags & FOLL_GET)) + return -EINVAL; + + /* + * FIXME: as noted in the get_user_pages_remote() implementation, it + * is not yet possible to safely set FOLL_LONGTERM here. FOLL_LONGTERM + * needs to be set, but for now the best we can do is a "TODO" item. + */ + gup_flags |= FOLL_REMOTE | FOLL_PIN; + + return __get_user_pages_locked(tsk, mm, start, nr_pages, pages, vmas, + locked, gup_flags); +} +EXPORT_SYMBOL(pin_longterm_pages_remote); + +/** + * pin_user_pages() - pin user pages in memory for use by other devices + * + * Nearly the same as get_user_pages(), except that FOLL_TOUCH is not set, and + * FOLL_PIN is set. + * + * FOLL_PIN means that the pages must be released via put_user_page(). Please + * see Documentation/vm/pin_user_pages.rst for details. + * + * This is intended for Case 1 (DIO) in Documentation/vm/pin_user_pages.rst. It + * is NOT intended for Case 2 (RDMA: long-term pins). + */ +long pin_user_pages(unsigned long start, unsigned long nr_pages, + unsigned int gup_flags, struct page **pages, + struct vm_area_struct **vmas) +{ + /* FOLL_GET and FOLL_PIN are mutually exclusive. */ + if (WARN_ON_ONCE(gup_flags & FOLL_GET)) + return -EINVAL; + + gup_flags |= FOLL_PIN; + return __gup_longterm_locked(current, current->mm, start, nr_pages, + pages, vmas, gup_flags); +} +EXPORT_SYMBOL(pin_user_pages); + +/** + * pin_longterm_pages() - pin user pages in memory for long-term use (RDMA, + * typically) + * + * Nearly the same as get_user_pages(), except that FOLL_PIN and FOLL_LONGTERM + * are set. See get_user_pages_fast() for documentation on the function + * arguments, because the arguments here are identical. + * + * FOLL_PIN means that the pages must be released via put_user_page(). Please + * see Documentation/vm/pin_user_pages.rst for further details. + * + * FOLL_LONGTERM means that the pages are being pinned for "long term" use, + * typically by a non-CPU device, and we cannot be sure that waiting for a + * pinned page to become unpin will be effective. + * + * This is intended for Case 2 (RDMA: long-term pins) in + * Documentation/vm/pin_user_pages.rst. + */ +long pin_longterm_pages(unsigned long start, unsigned long nr_pages, + unsigned int gup_flags, struct page **pages, + struct vm_area_struct **vmas) +{ + /* FOLL_GET and FOLL_PIN are mutually exclusive. */ + if (WARN_ON_ONCE(gup_flags & FOLL_GET)) + return -EINVAL; + + gup_flags |= FOLL_PIN | FOLL_LONGTERM; + return __gup_longterm_locked(current, current->mm, start, nr_pages, + pages, vmas, gup_flags); +} +EXPORT_SYMBOL(pin_longterm_pages);
Introduce pin_user_pages*() variations of get_user_pages*() calls, and also pin_longterm_pages*() variations. These variants all set FOLL_PIN, which is also introduced, and basically documented. (An upcoming patch provides more extensive documentation.) The second set (pin_longterm*) also sets FOLL_LONGTERM: pin_user_pages() pin_user_pages_remote() pin_user_pages_fast() pin_longterm_pages() pin_longterm_pages_remote() pin_longterm_pages_fast() All pages that are pinned via the above calls, must be unpinned via put_user_page(). The underlying rules are: * These are gup-internal flags, so the call sites should not directly set FOLL_PIN nor FOLL_LONGTERM. That behavior is enforced with assertions, for the new FOLL_PIN flag. However, for the pre-existing FOLL_LONGTERM flag, which has some call sites that still directly set FOLL_LONGTERM, there is no assertion yet. * Call sites that want to indicate that they are going to do DirectIO ("DIO") or something with similar characteristics, should call a get_user_pages()-like wrapper call that sets FOLL_PIN. These wrappers will: * Start with "pin_user_pages" instead of "get_user_pages". That makes it easy to find and audit the call sites. * Set FOLL_PIN * For pages that are received via FOLL_PIN, those pages must be returned via put_user_page(). Signed-off-by: John Hubbard <jhubbard@nvidia.com> --- include/linux/mm.h | 53 ++++++++- mm/gup.c | 284 +++++++++++++++++++++++++++++++++++++++++---- 2 files changed, 311 insertions(+), 26 deletions(-)