| Message ID | 20210714222117.47648-7-peterx@redhat.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | userfaultfd-wp: Support shmem and hugetlbfs | expand |
Hi Peter,
Thank you for the patch! Yet something to improve:
[auto build test ERROR on linus/master]
[also build test ERROR on v5.14-rc1 next-20210714]
[cannot apply to hnaz-linux-mm/master asm-generic/master linux/master]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch]
url: https://github.com/0day-ci/linux/commits/Peter-Xu/userfaultfd-wp-Support-shmem-and-hugetlbfs/20210715-062718
base: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git 8096acd7442e613fad0354fc8dfdb2003cceea0b
config: x86_64-randconfig-r021-20210714 (attached as .config)
compiler: clang version 13.0.0 (https://github.com/llvm/llvm-project 0e49c54a8cbd3e779e5526a5888c683c01cc3c50)
reproduce (this is a W=1 build):
wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
chmod +x ~/bin/make.cross
# install x86_64 cross compiling tool for clang build
# apt-get install binutils-x86-64-linux-gnu
# https://github.com/0day-ci/linux/commit/8b3e70f40b8333a803e642ed5c8cce738985881c
git remote add linux-review https://github.com/0day-ci/linux
git fetch --no-tags linux-review Peter-Xu/userfaultfd-wp-Support-shmem-and-hugetlbfs/20210715-062718
git checkout 8b3e70f40b8333a803e642ed5c8cce738985881c
# save the attached .config to linux build tree
COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross ARCH=x86_64
If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@intel.com>
All errors (new ones prefixed by >>):
>> mm/memory.c:4167:6: error: implicit declaration of function 'uffd_disable_fault_around' [-Werror,-Wimplicit-function-declaration]
if (uffd_disable_fault_around(vmf->vma))
^
1 error generated.
vim +/uffd_disable_fault_around +4167 mm/memory.c
4159
4160 /* Return true if we should do read fault-around, false otherwise */
4161 static inline bool should_fault_around(struct vm_fault *vmf)
4162 {
4163 /* No ->map_pages? No way to fault around... */
4164 if (!vmf->vma->vm_ops->map_pages)
4165 return false;
4166
> 4167 if (uffd_disable_fault_around(vmf->vma))
4168 return false;
4169
4170 return fault_around_bytes >> PAGE_SHIFT > 1;
4171 }
4172
---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org
On Thu, Jul 15, 2021 at 02:20:21PM +0800, kernel test robot wrote: > Hi Peter, > > Thank you for the patch! Yet something to improve: > > [auto build test ERROR on linus/master] > [also build test ERROR on v5.14-rc1 next-20210714] > [cannot apply to hnaz-linux-mm/master asm-generic/master linux/master] > [If your patch is applied to the wrong git tree, kindly drop us a note. > And when submitting patch, we suggest to use '--base' as documented in > https://git-scm.com/docs/git-format-patch] > > url: https://github.com/0day-ci/linux/commits/Peter-Xu/userfaultfd-wp-Support-shmem-and-hugetlbfs/20210715-062718 > base: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git 8096acd7442e613fad0354fc8dfdb2003cceea0b > config: x86_64-randconfig-r021-20210714 (attached as .config) > compiler: clang version 13.0.0 (https://github.com/llvm/llvm-project 0e49c54a8cbd3e779e5526a5888c683c01cc3c50) > reproduce (this is a W=1 build): > wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross > chmod +x ~/bin/make.cross > # install x86_64 cross compiling tool for clang build > # apt-get install binutils-x86-64-linux-gnu > # https://github.com/0day-ci/linux/commit/8b3e70f40b8333a803e642ed5c8cce738985881c > git remote add linux-review https://github.com/0day-ci/linux > git fetch --no-tags linux-review Peter-Xu/userfaultfd-wp-Support-shmem-and-hugetlbfs/20210715-062718 > git checkout 8b3e70f40b8333a803e642ed5c8cce738985881c > # save the attached .config to linux build tree > COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross ARCH=x86_64 > > If you fix the issue, kindly add following tag as appropriate > Reported-by: kernel test robot <lkp@intel.com> > > All errors (new ones prefixed by >>): > > >> mm/memory.c:4167:6: error: implicit declaration of function 'uffd_disable_fault_around' [-Werror,-Wimplicit-function-declaration] > if (uffd_disable_fault_around(vmf->vma)) > ^ > 1 error generated. > > > vim +/uffd_disable_fault_around +4167 mm/memory.c > > 4159 > 4160 /* Return true if we should do read fault-around, false otherwise */ > 4161 static inline bool should_fault_around(struct vm_fault *vmf) > 4162 { > 4163 /* No ->map_pages? No way to fault around... */ > 4164 if (!vmf->vma->vm_ops->map_pages) > 4165 return false; > 4166 > > 4167 if (uffd_disable_fault_around(vmf->vma)) > 4168 return false; > 4169 > 4170 return fault_around_bytes >> PAGE_SHIFT > 1; > 4171 } > 4172 > > --- > 0-DAY CI Kernel Test Service, Intel Corporation > https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org Will squash this into the patch: ---8<--- diff --git a/include/linux/userfaultfd_k.h b/include/linux/userfaultfd_k.h index c4228acd1d80..4382240de7c3 100644 --- a/include/linux/userfaultfd_k.h +++ b/include/linux/userfaultfd_k.h @@ -283,6 +283,11 @@ static inline bool pte_swp_uffd_wp_special(pte_t pte) return false; } +static inline bool uffd_disable_fault_around(struct vm_area_struct *vma) +{ + return false; +} + #endif /* CONFIG_USERFAULTFD */ #endif /* _LINUX_USERFAULTFD_K_H */ ---8<--- Thanks,
diff --git a/include/linux/userfaultfd_k.h b/include/linux/userfaultfd_k.h index bb5a72a2b07a..47c74ef635ab 100644 --- a/include/linux/userfaultfd_k.h +++ b/include/linux/userfaultfd_k.h @@ -94,6 +94,18 @@ static inline bool uffd_disable_huge_pmd_share(struct vm_area_struct *vma) return vma->vm_flags & (VM_UFFD_WP | VM_UFFD_MINOR); } +/* + * Don't do fault around for either WP or MINOR registered uffd range. For + * MINOR registered range, fault around will be a total disaster and ptes can + * be installed without notifications; for WP it should mostly be fine as long + * as the fault around checks for pte_none() before the installation, however + * to be super safe we just forbid it. + */ +static inline bool uffd_disable_fault_around(struct vm_area_struct *vma) +{ + return vma->vm_flags & (VM_UFFD_WP | VM_UFFD_MINOR); +} + static inline bool userfaultfd_missing(struct vm_area_struct *vma) { return vma->vm_flags & VM_UFFD_MISSING; diff --git a/mm/memory.c b/mm/memory.c index 998a4f9a3744..ba8033ca6682 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -3964,6 +3964,7 @@ vm_fault_t do_set_pmd(struct vm_fault *vmf, struct page *page) void do_set_pte(struct vm_fault *vmf, struct page *page, unsigned long addr) { struct vm_area_struct *vma = vmf->vma; + bool uffd_wp = pte_swp_uffd_wp_special(vmf->orig_pte); bool write = vmf->flags & FAULT_FLAG_WRITE; bool prefault = vmf->address != addr; pte_t entry; @@ -3978,6 +3979,8 @@ void do_set_pte(struct vm_fault *vmf, struct page *page, unsigned long addr) if (write) entry = maybe_mkwrite(pte_mkdirty(entry), vma); + if (unlikely(uffd_wp)) + entry = pte_mkuffd_wp(pte_wrprotect(entry)); /* copy-on-write page */ if (write && !(vma->vm_flags & VM_SHARED)) { inc_mm_counter_fast(vma->vm_mm, MM_ANONPAGES); @@ -4045,8 +4048,12 @@ vm_fault_t finish_fault(struct vm_fault *vmf) vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd, vmf->address, &vmf->ptl); ret = 0; - /* Re-check under ptl */ - if (likely(pte_none(*vmf->pte))) + + /* + * Re-check under ptl. Note: this will cover both none pte and + * uffd-wp-special swap pte + */ + if (likely(pte_same(*vmf->pte, vmf->orig_pte))) do_set_pte(vmf, page, vmf->address); else ret = VM_FAULT_NOPAGE; @@ -4150,9 +4157,21 @@ static vm_fault_t do_fault_around(struct vm_fault *vmf) return vmf->vma->vm_ops->map_pages(vmf, start_pgoff, end_pgoff); } +/* Return true if we should do read fault-around, false otherwise */ +static inline bool should_fault_around(struct vm_fault *vmf) +{ + /* No ->map_pages? No way to fault around... */ + if (!vmf->vma->vm_ops->map_pages) + return false; + + if (uffd_disable_fault_around(vmf->vma)) + return false; + + return fault_around_bytes >> PAGE_SHIFT > 1; +} + static vm_fault_t do_read_fault(struct vm_fault *vmf) { - struct vm_area_struct *vma = vmf->vma; vm_fault_t ret = 0; /* @@ -4160,12 +4179,10 @@ static vm_fault_t do_read_fault(struct vm_fault *vmf) * if page by the offset is not ready to be mapped (cold cache or * something). */ - if (vma->vm_ops->map_pages && fault_around_bytes >> PAGE_SHIFT > 1) { - if (likely(!userfaultfd_minor(vmf->vma))) { - ret = do_fault_around(vmf); - if (ret) - return ret; - } + if (should_fault_around(vmf)) { + ret = do_fault_around(vmf); + if (ret) + return ret; } ret = __do_fault(vmf); @@ -4484,6 +4501,57 @@ static vm_fault_t wp_huge_pud(struct vm_fault *vmf, pud_t orig_pud) return VM_FAULT_FALLBACK; } +static vm_fault_t uffd_wp_clear_special(struct vm_fault *vmf) +{ + vmf->pte = pte_offset_map_lock(vmf->vma->vm_mm, vmf->pmd, + vmf->address, &vmf->ptl); + /* + * Be careful so that we will only recover a special uffd-wp pte into a + * none pte. Otherwise it means the pte could have changed, so retry. + */ + if (pte_swp_uffd_wp_special(*vmf->pte)) + pte_clear(vmf->vma->vm_mm, vmf->address, vmf->pte); + pte_unmap_unlock(vmf->pte, vmf->ptl); + return 0; +} + +/* + * This is actually a page-missing access, but with uffd-wp special pte + * installed. It means this pte was wr-protected before being unmapped. + */ +static vm_fault_t uffd_wp_handle_special(struct vm_fault *vmf) +{ + /* Careful! vmf->pte unmapped after return */ + if (!pte_unmap_same(vmf)) + return 0; + + /* + * Just in case there're leftover special ptes even after the region + * got unregistered - we can simply clear them. + */ + if (unlikely(!userfaultfd_wp(vmf->vma) || vma_is_anonymous(vmf->vma))) + return uffd_wp_clear_special(vmf); + + /* + * Here we share most code with do_fault(), in which we can identify + * whether this is "none pte fault" or "uffd-wp-special fault" by + * checking the vmf->orig_pte. + */ + return do_fault(vmf); +} + +static vm_fault_t do_swap_pte(struct vm_fault *vmf) +{ + /* + * We need to handle special swap ptes before handling ptes that + * contain swap entries, always. + */ + if (unlikely(pte_swp_uffd_wp_special(vmf->orig_pte))) + return uffd_wp_handle_special(vmf); + + return do_swap_page(vmf); +} + /* * These routines also need to handle stuff like marking pages dirty * and/or accessed for architectures that don't do it in hardware (most @@ -4558,7 +4626,7 @@ static vm_fault_t handle_pte_fault(struct vm_fault *vmf) } if (!pte_present(vmf->orig_pte)) - return do_swap_page(vmf); + return do_swap_pte(vmf); if (pte_protnone(vmf->orig_pte) && vma_is_accessible(vmf->vma)) return do_numa_page(vmf);
File-backed memories are prone to unmap/swap so the ptes are always unstable. This could lead to userfaultfd-wp information got lost when unmapped or swapped out on such types of memory, for example, shmem. To keep such an information persistent, we will start to use the newly introduced swap-like special ptes to replace a null pte when those ptes were removed. Prepare this by handling such a special pte first before it is applied in the general page fault handler. The handling of this special pte page fault is similar to missing fault, but it should happen after the pte missing logic since the special pte is designed to be a swap-like pte. Meanwhile it should be handled before do_swap_page() so that the swap core logic won't be confused to see such an illegal swap pte. This is a slow path of uffd-wp handling, because unmap of wr-protected shmem ptes should be rare. So far it should only trigger in two conditions: (1) When trying to punch holes in shmem_fallocate(), there will be a pre-unmap optimization before evicting the page. That will create unmapped shmem ptes with wr-protected pages covered. (2) Swapping out of shmem pages Because of this, the page fault handling is simplifed too by not sending the wr-protect message in the 1st page fault, instead the page will be installed read-only, so the message will be generated until the next write, which will trigger the do_wp_page() path of general uffd-wp handling. Disable fault-around for all uffd-wp registered ranges for extra safety, and clean the code up a bit after we introduced MINOR fault. Signed-off-by: Peter Xu <peterx@redhat.com> --- include/linux/userfaultfd_k.h | 12 +++++ mm/memory.c | 88 +++++++++++++++++++++++++++++++---- 2 files changed, 90 insertions(+), 10 deletions(-)