| Message ID | 1-v2-dfe9ecdb6c74+2066-gup_fork_jgg@nvidia.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Add a seqcount between gup_fast and copy_page_range() | expand |
On Fri 30-10-20 11:46:20, Jason Gunthorpe wrote: > The next patch in this series makes the lockless flow a little more > complex, so move the entire block into a new function and remove a level > of indention. Tidy a bit of cruft: > > - addr is always the same as start, so use start > > - Use the modern check_add_overflow() for computing end = start + len > > - nr_pinned/pages << PAGE_SHIFT needs the LHS to be unsigned long to > avoid shift overflow, make the variables unsigned long to avoid coding > casts in both places. nr_pinned was missing its cast > > - The handling of ret and nr_pinned can be streamlined a bit > > No functional change. > > Signed-off-by: Jason Gunthorpe <jgg@nvidia.com> Looks good to me. You can add: Reviewed-by: Jan Kara <jack@suse.cz> Honza > --- > mm/gup.c | 99 ++++++++++++++++++++++++++++++-------------------------- > 1 file changed, 54 insertions(+), 45 deletions(-) > > diff --git a/mm/gup.c b/mm/gup.c > index 102877ed77a4b4..150cc962c99201 100644 > --- a/mm/gup.c > +++ b/mm/gup.c > @@ -2671,13 +2671,43 @@ static int __gup_longterm_unlocked(unsigned long start, int nr_pages, > return ret; > } > > -static int internal_get_user_pages_fast(unsigned long start, int nr_pages, > +static unsigned long lockless_pages_from_mm(unsigned long start, > + unsigned long end, > + unsigned int gup_flags, > + struct page **pages) > +{ > + unsigned long flags; > + int nr_pinned = 0; > + > + if (!IS_ENABLED(CONFIG_HAVE_FAST_GUP) || > + !gup_fast_permitted(start, end)) > + return 0; > + > + /* > + * Disable interrupts. The nested form is used, in order to allow full, > + * general purpose use of this routine. > + * > + * With interrupts disabled, we block page table pages from being freed > + * from under us. See struct mmu_table_batch comments in > + * include/asm-generic/tlb.h for more details. > + * > + * We do not adopt an rcu_read_lock() here as we also want to block IPIs > + * that come from THPs splitting. > + */ > + local_irq_save(flags); > + gup_pgd_range(start, end, gup_flags, pages, &nr_pinned); > + local_irq_restore(flags); > + return nr_pinned; > +} > + > +static int internal_get_user_pages_fast(unsigned long start, > + unsigned long nr_pages, > unsigned int gup_flags, > struct page **pages) > { > - unsigned long addr, len, end; > - unsigned long flags; > - int nr_pinned = 0, ret = 0; > + unsigned long len, end; > + unsigned long nr_pinned; > + int ret; > > if (WARN_ON_ONCE(gup_flags & ~(FOLL_WRITE | FOLL_LONGTERM | > FOLL_FORCE | FOLL_PIN | FOLL_GET | > @@ -2691,54 +2721,33 @@ static int internal_get_user_pages_fast(unsigned long start, int nr_pages, > might_lock_read(¤t->mm->mmap_lock); > > start = untagged_addr(start) & PAGE_MASK; > - addr = start; > - len = (unsigned long) nr_pages << PAGE_SHIFT; > - end = start + len; > - > - if (end <= start) > + len = nr_pages << PAGE_SHIFT; > + if (check_add_overflow(start, len, &end)) > return 0; > if (unlikely(!access_ok((void __user *)start, len))) > return -EFAULT; > > - /* > - * Disable interrupts. The nested form is used, in order to allow > - * full, general purpose use of this routine. > - * > - * With interrupts disabled, we block page table pages from being > - * freed from under us. See struct mmu_table_batch comments in > - * include/asm-generic/tlb.h for more details. > - * > - * We do not adopt an rcu_read_lock(.) here as we also want to > - * block IPIs that come from THPs splitting. > - */ > - if (IS_ENABLED(CONFIG_HAVE_FAST_GUP) && gup_fast_permitted(start, end)) { > - unsigned long fast_flags = gup_flags; > - > - local_irq_save(flags); > - gup_pgd_range(addr, end, fast_flags, pages, &nr_pinned); > - local_irq_restore(flags); > - ret = nr_pinned; > - } > + nr_pinned = lockless_pages_from_mm(start, end, gup_flags, pages); > + if (nr_pinned == nr_pages || gup_flags & FOLL_FAST_ONLY) > + return nr_pinned; > > - if (nr_pinned < nr_pages && !(gup_flags & FOLL_FAST_ONLY)) { > - /* Try to get the remaining pages with get_user_pages */ > - start += nr_pinned << PAGE_SHIFT; > - pages += nr_pinned; > - > - ret = __gup_longterm_unlocked(start, nr_pages - nr_pinned, > - gup_flags, pages); > - > - /* Have to be a bit careful with return values */ > - if (nr_pinned > 0) { > - if (ret < 0) > - ret = nr_pinned; > - else > - ret += nr_pinned; > - } > + /* Slow path: try to get the remaining pages with get_user_pages */ > + start += nr_pinned << PAGE_SHIFT; > + pages += nr_pinned; > + ret = __gup_longterm_unlocked(start, nr_pages - nr_pinned, gup_flags, > + pages); > + if (ret < 0) { > + /* > + * The caller has to unpin the pages we already pinned so > + * returning -errno is not an option > + */ > + if (nr_pinned) > + return nr_pinned; > + return ret; > } > - > - return ret; > + return ret + nr_pinned; > } > + > /** > * get_user_pages_fast_only() - pin user pages in memory > * @start: starting user address > -- > 2.28.0 >
On 10/30/20 7:46 AM, Jason Gunthorpe wrote: > The next patch in this series makes the lockless flow a little more > complex, so move the entire block into a new function and remove a level > of indention. Tidy a bit of cruft: > > - addr is always the same as start, so use start > > - Use the modern check_add_overflow() for computing end = start + len > > - nr_pinned/pages << PAGE_SHIFT needs the LHS to be unsigned long to > avoid shift overflow, make the variables unsigned long to avoid coding > casts in both places. nr_pinned was missing its cast > > - The handling of ret and nr_pinned can be streamlined a bit > > No functional change. > > Signed-off-by: Jason Gunthorpe <jgg@nvidia.com> > --- > mm/gup.c | 99 ++++++++++++++++++++++++++++++-------------------------- > 1 file changed, 54 insertions(+), 45 deletions(-) Everything still looks correct. Reviewed-by: John Hubbard <jhubbard@nvidia.com> thanks,
On Fri, Oct 30, 2020 at 11:46:20AM -0300, Jason Gunthorpe wrote: > The next patch in this series makes the lockless flow a little more > complex, so move the entire block into a new function and remove a level > of indention. Tidy a bit of cruft: > > - addr is always the same as start, so use start > > - Use the modern check_add_overflow() for computing end = start + len > > - nr_pinned/pages << PAGE_SHIFT needs the LHS to be unsigned long to > avoid shift overflow, make the variables unsigned long to avoid coding > casts in both places. nr_pinned was missing its cast > > - The handling of ret and nr_pinned can be streamlined a bit > > No functional change. > > Signed-off-by: Jason Gunthorpe <jgg@nvidia.com> Sorry for a very late reply (due to other distractions): Reviewed-by: Peter Xu <peterx@redhat.com> Thanks,
diff --git a/mm/gup.c b/mm/gup.c index 102877ed77a4b4..150cc962c99201 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -2671,13 +2671,43 @@ static int __gup_longterm_unlocked(unsigned long start, int nr_pages, return ret; } -static int internal_get_user_pages_fast(unsigned long start, int nr_pages, +static unsigned long lockless_pages_from_mm(unsigned long start, + unsigned long end, + unsigned int gup_flags, + struct page **pages) +{ + unsigned long flags; + int nr_pinned = 0; + + if (!IS_ENABLED(CONFIG_HAVE_FAST_GUP) || + !gup_fast_permitted(start, end)) + return 0; + + /* + * Disable interrupts. The nested form is used, in order to allow full, + * general purpose use of this routine. + * + * With interrupts disabled, we block page table pages from being freed + * from under us. See struct mmu_table_batch comments in + * include/asm-generic/tlb.h for more details. + * + * We do not adopt an rcu_read_lock() here as we also want to block IPIs + * that come from THPs splitting. + */ + local_irq_save(flags); + gup_pgd_range(start, end, gup_flags, pages, &nr_pinned); + local_irq_restore(flags); + return nr_pinned; +} + +static int internal_get_user_pages_fast(unsigned long start, + unsigned long nr_pages, unsigned int gup_flags, struct page **pages) { - unsigned long addr, len, end; - unsigned long flags; - int nr_pinned = 0, ret = 0; + unsigned long len, end; + unsigned long nr_pinned; + int ret; if (WARN_ON_ONCE(gup_flags & ~(FOLL_WRITE | FOLL_LONGTERM | FOLL_FORCE | FOLL_PIN | FOLL_GET | @@ -2691,54 +2721,33 @@ static int internal_get_user_pages_fast(unsigned long start, int nr_pages, might_lock_read(¤t->mm->mmap_lock); start = untagged_addr(start) & PAGE_MASK; - addr = start; - len = (unsigned long) nr_pages << PAGE_SHIFT; - end = start + len; - - if (end <= start) + len = nr_pages << PAGE_SHIFT; + if (check_add_overflow(start, len, &end)) return 0; if (unlikely(!access_ok((void __user *)start, len))) return -EFAULT; - /* - * Disable interrupts. The nested form is used, in order to allow - * full, general purpose use of this routine. - * - * With interrupts disabled, we block page table pages from being - * freed from under us. See struct mmu_table_batch comments in - * include/asm-generic/tlb.h for more details. - * - * We do not adopt an rcu_read_lock(.) here as we also want to - * block IPIs that come from THPs splitting. - */ - if (IS_ENABLED(CONFIG_HAVE_FAST_GUP) && gup_fast_permitted(start, end)) { - unsigned long fast_flags = gup_flags; - - local_irq_save(flags); - gup_pgd_range(addr, end, fast_flags, pages, &nr_pinned); - local_irq_restore(flags); - ret = nr_pinned; - } + nr_pinned = lockless_pages_from_mm(start, end, gup_flags, pages); + if (nr_pinned == nr_pages || gup_flags & FOLL_FAST_ONLY) + return nr_pinned; - if (nr_pinned < nr_pages && !(gup_flags & FOLL_FAST_ONLY)) { - /* Try to get the remaining pages with get_user_pages */ - start += nr_pinned << PAGE_SHIFT; - pages += nr_pinned; - - ret = __gup_longterm_unlocked(start, nr_pages - nr_pinned, - gup_flags, pages); - - /* Have to be a bit careful with return values */ - if (nr_pinned > 0) { - if (ret < 0) - ret = nr_pinned; - else - ret += nr_pinned; - } + /* Slow path: try to get the remaining pages with get_user_pages */ + start += nr_pinned << PAGE_SHIFT; + pages += nr_pinned; + ret = __gup_longterm_unlocked(start, nr_pages - nr_pinned, gup_flags, + pages); + if (ret < 0) { + /* + * The caller has to unpin the pages we already pinned so + * returning -errno is not an option + */ + if (nr_pinned) + return nr_pinned; + return ret; } - - return ret; + return ret + nr_pinned; } + /** * get_user_pages_fast_only() - pin user pages in memory * @start: starting user address
The next patch in this series makes the lockless flow a little more complex, so move the entire block into a new function and remove a level of indention. Tidy a bit of cruft: - addr is always the same as start, so use start - Use the modern check_add_overflow() for computing end = start + len - nr_pinned/pages << PAGE_SHIFT needs the LHS to be unsigned long to avoid shift overflow, make the variables unsigned long to avoid coding casts in both places. nr_pinned was missing its cast - The handling of ret and nr_pinned can be streamlined a bit No functional change. Signed-off-by: Jason Gunthorpe <jgg@nvidia.com> --- mm/gup.c | 99 ++++++++++++++++++++++++++++++-------------------------- 1 file changed, 54 insertions(+), 45 deletions(-)