Re: [PATCH v5 17/26] hugetlb/userfaultfd: Hook page faults for uffd write protection

kernel test robot
2021-07-20T15:44:32Z

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Hi Peter,

Thank you for the patch! Yet something to improve:

[auto build test ERROR on kselftest/next]
[also build test ERROR on linus/master v5.14-rc2 next-20210720]
[cannot apply to hnaz-linux-mm/master asm-generic/master arm64/for-next/core linux/master tip/x86/core]
[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/20210716-041947
base: https://git.kernel.org/pub/scm/linux/kernel/git/shuah/linux-kselftest.git next
config: s390-randconfig-r023-20210716 (attached as .config)
compiler: clang version 13.0.0 (https://github.com/llvm/llvm-project 5d5b08761f944d5b9822d582378333cc4b36a0a7)
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 s390 cross compiling tool for clang build
# apt-get install binutils-s390x-linux-gnu
# https://github.com/0day-ci/linux/commit/071935856c8e636cafde633db59259d75069cc8f
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/20210716-041947
git checkout 071935856c8e636cafde633db59259d75069cc8f
# save the attached .config to linux build tree
COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross ARCH=s390

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 >>):

In file included from mm/hugetlb.c:19:
In file included from include/linux/memblock.h:14:
In file included from arch/s390/include/asm/dma.h:5:
In file included from arch/s390/include/asm/io.h:75:
include/asm-generic/io.h:464:31: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
val = __raw_readb(PCI_IOBASE + addr);
~~~~~~~~~~ ^
include/asm-generic/io.h:477:61: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
val = __le16_to_cpu((__le16 __force)__raw_readw(PCI_IOBASE + addr));
~~~~~~~~~~ ^
include/uapi/linux/byteorder/big_endian.h:36:59: note: expanded from macro '__le16_to_cpu'
#define __le16_to_cpu(x) __swab16((__force __u16)(__le16)(x))
^
include/uapi/linux/swab.h:102:54: note: expanded from macro '__swab16'
#define __swab16(x) (__u16)__builtin_bswap16((__u16)(x))
^
In file included from mm/hugetlb.c:19:
In file included from include/linux/memblock.h:14:
In file included from arch/s390/include/asm/dma.h:5:
In file included from arch/s390/include/asm/io.h:75:
include/asm-generic/io.h:490:61: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
val = __le32_to_cpu((__le32 __force)__raw_readl(PCI_IOBASE + addr));
~~~~~~~~~~ ^
include/uapi/linux/byteorder/big_endian.h:34:59: note: expanded from macro '__le32_to_cpu'
#define __le32_to_cpu(x) __swab32((__force __u32)(__le32)(x))
^
include/uapi/linux/swab.h:115:54: note: expanded from macro '__swab32'
#define __swab32(x) (__u32)__builtin_bswap32((__u32)(x))
^
In file included from mm/hugetlb.c:19:
In file included from include/linux/memblock.h:14:
In file included from arch/s390/include/asm/dma.h:5:
In file included from arch/s390/include/asm/io.h:75:
include/asm-generic/io.h:501:33: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
__raw_writeb(value, PCI_IOBASE + addr);
~~~~~~~~~~ ^
include/asm-generic/io.h:511:59: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
__raw_writew((u16 __force)cpu_to_le16(value), PCI_IOBASE + addr);
~~~~~~~~~~ ^
include/asm-generic/io.h:521:59: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
__raw_writel((u32 __force)cpu_to_le32(value), PCI_IOBASE + addr);
~~~~~~~~~~ ^
include/asm-generic/io.h:609:20: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
readsb(PCI_IOBASE + addr, buffer, count);
~~~~~~~~~~ ^
include/asm-generic/io.h:617:20: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
readsw(PCI_IOBASE + addr, buffer, count);
~~~~~~~~~~ ^
include/asm-generic/io.h:625:20: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
readsl(PCI_IOBASE + addr, buffer, count);
~~~~~~~~~~ ^
include/asm-generic/io.h:634:21: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
writesb(PCI_IOBASE + addr, buffer, count);
~~~~~~~~~~ ^
include/asm-generic/io.h:643:21: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
writesw(PCI_IOBASE + addr, buffer, count);
~~~~~~~~~~ ^
include/asm-generic/io.h:652:21: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
writesl(PCI_IOBASE + addr, buffer, count);
~~~~~~~~~~ ^
>> mm/hugetlb.c:5063:29: error: implicit declaration of function 'huge_pte_uffd_wp' [-Werror,-Wimplicit-function-declaration]
if (userfaultfd_wp(vma) && huge_pte_uffd_wp(huge_ptep_get(ptep)) &&
^
12 warnings and 1 error generated.

vim +/huge_pte_uffd_wp +5063 mm/hugetlb.c

4957
4958 vm_fault_t hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma,
4959 unsigned long address, unsigned int flags)
4960 {
4961 pte_t *ptep, entry;
4962 spinlock_t *ptl;
4963 vm_fault_t ret;
4964 u32 hash;
4965 pgoff_t idx;
4966 struct page *page = NULL;
4967 struct page *pagecache_page = NULL;
4968 struct hstate *h = hstate_vma(vma);
4969 struct address_space *mapping;
4970 int need_wait_lock = 0;
4971 unsigned long haddr = address & huge_page_mask(h);
4972
4973 ptep = huge_pte_offset(mm, haddr, huge_page_size(h));
4974 if (ptep) {
4975 /*
4976 * Since we hold no locks, ptep could be stale. That is
4977 * OK as we are only making decisions based on content and
4978 * not actually modifying content here.
4979 */
4980 entry = huge_ptep_get(ptep);
4981 if (unlikely(is_hugetlb_entry_migration(entry))) {
4982 migration_entry_wait_huge(vma, mm, ptep);
4983 return 0;
4984 } else if (unlikely(is_hugetlb_entry_hwpoisoned(entry)))
4985 return VM_FAULT_HWPOISON_LARGE |
4986 VM_FAULT_SET_HINDEX(hstate_index(h));
4987 }
4988
4989 /*
4990 * Acquire i_mmap_rwsem before calling huge_pte_alloc and hold
4991 * until finished with ptep. This serves two purposes:
4992 * 1) It prevents huge_pmd_unshare from being called elsewhere
4993 * and making the ptep no longer valid.
4994 * 2) It synchronizes us with i_size modifications during truncation.
4995 *
4996 * ptep could have already be assigned via huge_pte_offset. That
4997 * is OK, as huge_pte_alloc will return the same value unless
4998 * something has changed.
4999 */
5000 mapping = vma->vm_file->f_mapping;
5001 i_mmap_lock_read(mapping);
5002 ptep = huge_pte_alloc(mm, vma, haddr, huge_page_size(h));
5003 if (!ptep) {
5004 i_mmap_unlock_read(mapping);
5005 return VM_FAULT_OOM;
5006 }
5007
5008 /*
5009 * Serialize hugepage allocation and instantiation, so that we don't
5010 * get spurious allocation failures if two CPUs race to instantiate
5011 * the same page in the page cache.
5012 */
5013 idx = vma_hugecache_offset(h, vma, haddr);
5014 hash = hugetlb_fault_mutex_hash(mapping, idx);
5015 mutex_lock(&hugetlb_fault_mutex_table[hash]);
5016
5017 entry = huge_ptep_get(ptep);
5018 if (huge_pte_none(entry)) {
5019 ret = hugetlb_no_page(mm, vma, mapping, idx, address, ptep, flags);
5020 goto out_mutex;
5021 }
5022
5023 ret = 0;
5024
5025 /*
5026 * entry could be a migration/hwpoison entry at this point, so this
5027 * check prevents the kernel from going below assuming that we have
5028 * an active hugepage in pagecache. This goto expects the 2nd page
5029 * fault, and is_hugetlb_entry_(migration|hwpoisoned) check will
5030 * properly handle it.
5031 */
5032 if (!pte_present(entry))
5033 goto out_mutex;
5034
5035 /*
5036 * If we are going to COW the mapping later, we examine the pending
5037 * reservations for this page now. This will ensure that any
5038 * allocations necessary to record that reservation occur outside the
5039 * spinlock. For private mappings, we also lookup the pagecache
5040 * page now as it is used to determine if a reservation has been
5041 * consumed.
5042 */
5043 if ((flags & FAULT_FLAG_WRITE) && !huge_pte_write(entry)) {
5044 if (vma_needs_reservation(h, vma, haddr) < 0) {
5045 ret = VM_FAULT_OOM;
5046 goto out_mutex;
5047 }
5048 /* Just decrements count, does not deallocate */
5049 vma_end_reservation(h, vma, haddr);
5050
5051 if (!(vma->vm_flags & VM_MAYSHARE))
5052 pagecache_page = hugetlbfs_pagecache_page(h,
5053 vma, haddr);
5054 }
5055
5056 ptl = huge_pte_lock(h, mm, ptep);
5057
5058 /* Check for a racing update before calling hugetlb_cow */
5059 if (unlikely(!pte_same(entry, huge_ptep_get(ptep))))
5060 goto out_ptl;
5061
5062 /* Handle userfault-wp first, before trying to lock more pages */
> 5063 if (userfaultfd_wp(vma) && huge_pte_uffd_wp(huge_ptep_get(ptep)) &&
5064 (flags & FAULT_FLAG_WRITE) && !huge_pte_write(entry)) {
5065 struct vm_fault vmf = {
5066 .vma = vma,
5067 .address = haddr,
5068 .flags = flags,
5069 };
5070
5071 spin_unlock(ptl);
5072 if (pagecache_page) {
5073 unlock_page(pagecache_page);
5074 put_page(pagecache_page);
5075 }
5076 mutex_unlock(&hugetlb_fault_mutex_table[hash]);
5077 i_mmap_unlock_read(mapping);
5078 return handle_userfault(&vmf, VM_UFFD_WP);
5079 }
5080
5081 /*
5082 * hugetlb_cow() requires page locks of pte_page(entry) and
5083 * pagecache_page, so here we need take the former one
5084 * when page != pagecache_page or !pagecache_page.
5085 */
5086 page = pte_page(entry);
5087 if (page != pagecache_page)
5088 if (!trylock_page(page)) {
5089 need_wait_lock = 1;
5090 goto out_ptl;
5091 }
5092
5093 get_page(page);
5094
5095 if (flags & FAULT_FLAG_WRITE) {
5096 if (!huge_pte_write(entry)) {
5097 ret = hugetlb_cow(mm, vma, address, ptep,
5098 pagecache_page, ptl);
5099 goto out_put_page;
5100 }
5101 entry = huge_pte_mkdirty(entry);
5102 }
5103 entry = pte_mkyoung(entry);
5104 if (huge_ptep_set_access_flags(vma, haddr, ptep, entry,
5105 flags & FAULT_FLAG_WRITE))
5106 update_mmu_cache(vma, haddr, ptep);
5107 out_put_page:
5108 if (page != pagecache_page)
5109 unlock_page(page);
5110 put_page(page);
5111 out_ptl:
5112 spin_unlock(ptl);
5113
5114 if (pagecache_page) {
5115 unlock_page(pagecache_page);
5116 put_page(pagecache_page);
5117 }
5118 out_mutex:
5119 mutex_unlock(&hugetlb_fault_mutex_table[hash]);
5120 i_mmap_unlock_read(mapping);
5121 /*
5122 * Generally it's safe to hold refcount during waiting page lock. But
5123 * here we just wait to defer the next page fault to avoid busy loop and
5124 * the page is not used after unlocked before returning from the current
5125 * page fault. So we are safe from accessing freed page, even if we wait
5126 * here without taking refcount.
5127 */
5128 if (need_wait_lock)
5129 wait_on_page_locked(page);
5130 return ret;
5131 }
5132

---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org

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