Commit 670ddd8c authored by Hugh Dickins's avatar Hugh Dickins Committed by Andrew Morton
Browse files

mm/mprotect: delete pmd_none_or_clear_bad_unless_trans_huge() 

change_pmd_range() had special pmd_none_or_clear_bad_unless_trans_huge(),
required to avoid "bad" choices when setting automatic NUMA hinting under
mmap_read_lock(); but most of that is already covered in pte_offset_map()
now.  change_pmd_range() just wants a pmd_none() check before wasting time
on MMU notifiers, then checks on the read-once _pmd value to work out
what's needed for huge cases.  If change_pte_range() returns -EAGAIN to
retry if pte_offset_map_lock() fails, nothing more special is needed.

Link: https://lkml.kernel.org/r/725a42a9-91e9-c868-925-e3a5fd40bb4f@google.com


Signed-off-by: default avatarHugh Dickins <hughd@google.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: "Huang, Ying" <ying.huang@intel.com>
Cc: Ira Weiny <ira.weiny@intel.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Lorenzo Stoakes <lstoakes@gmail.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport (IBM) <rppt@kernel.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Naoya Horiguchi <naoya.horiguchi@nec.com>
Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Qi Zheng <zhengqi.arch@bytedance.com>
Cc: Ralph Campbell <rcampbell@nvidia.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: SeongJae Park <sj@kernel.org>
Cc: Song Liu <song@kernel.org>
Cc: Steven Price <steven.price@arm.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Cc: Will Deacon <will@kernel.org>
Cc: Yang Shi <shy828301@gmail.com>
Cc: Yu Zhao <yuzhao@google.com>
Cc: Zack Rusin <zackr@vmware.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 04dee9e8

mm/mprotect.c

+17 −57
Original line number Diff line number Diff line
@@ -93,22 +93,9 @@ static long change_pte_range(struct mmu_gather *tlb, 
	bool uffd_wp_resolve = cp_flags & MM_CP_UFFD_WP_RESOLVE;



	tlb_change_page_size(tlb, PAGE_SIZE);



	/*

	 * Can be called with only the mmap_lock for reading by

	 * prot_numa so we must check the pmd isn't constantly

	 * changing from under us from pmd_none to pmd_trans_huge

	 * and/or the other way around.

	 */

	if (pmd_trans_unstable(pmd))

		return 0;



	/*

	 * The pmd points to a regular pte so the pmd can't change

	 * from under us even if the mmap_lock is only hold for

	 * reading.

	 */

	pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);

	if (!pte)

		return -EAGAIN;



	/* Get target node for single threaded private VMAs */

	if (prot_numa && !(vma->vm_flags & VM_SHARED) &&
@@ -301,26 +288,6 @@ static long change_pte_range(struct mmu_gather *tlb, 
	return pages;

}



/*

 * Used when setting automatic NUMA hinting protection where it is

 * critical that a numa hinting PMD is not confused with a bad PMD.

 */

static inline int pmd_none_or_clear_bad_unless_trans_huge(pmd_t *pmd)

{

	pmd_t pmdval = pmdp_get_lockless(pmd);



	if (pmd_none(pmdval))

		return 1;

	if (pmd_trans_huge(pmdval))

		return 0;

	if (unlikely(pmd_bad(pmdval))) {

		pmd_clear_bad(pmd);

		return 1;

	}



	return 0;

}



/*

 * Return true if we want to split THPs into PTE mappings in change

 * protection procedure, false otherwise.
@@ -398,7 +365,8 @@ static inline long change_pmd_range(struct mmu_gather *tlb, 
	pmd = pmd_offset(pud, addr);

	do {

		long ret;



		pmd_t _pmd;

again:

		next = pmd_addr_end(addr, end);



		ret = change_pmd_prepare(vma, pmd, cp_flags);
@@ -406,16 +374,8 @@ static inline long change_pmd_range(struct mmu_gather *tlb, 
			pages = ret;

			break;

		}

		/*

		 * Automatic NUMA balancing walks the tables with mmap_lock

		 * held for read. It's possible a parallel update to occur

		 * between pmd_trans_huge() and a pmd_none_or_clear_bad()

		 * check leading to a false positive and clearing.

		 * Hence, it's necessary to atomically read the PMD value

		 * for all the checks.

		 */

		if (!is_swap_pmd(*pmd) && !pmd_devmap(*pmd) &&

		     pmd_none_or_clear_bad_unless_trans_huge(pmd))



		if (pmd_none(*pmd))

			goto next;



		/* invoke the mmu notifier if the pmd is populated */
@@ -426,7 +386,8 @@ static inline long change_pmd_range(struct mmu_gather *tlb, 
			mmu_notifier_invalidate_range_start(&range);

		}



		if (is_swap_pmd(*pmd) || pmd_trans_huge(*pmd) || pmd_devmap(*pmd)) {

		_pmd = pmdp_get_lockless(pmd);

		if (is_swap_pmd(_pmd) || pmd_trans_huge(_pmd) || pmd_devmap(_pmd)) {

			if ((next - addr != HPAGE_PMD_SIZE) ||

			    pgtable_split_needed(vma, cp_flags)) {

				__split_huge_pmd(vma, pmd, addr, false, NULL);
@@ -441,15 +402,10 @@ static inline long change_pmd_range(struct mmu_gather *tlb, 
					break;

				}

			} else {

				/*

				 * change_huge_pmd() does not defer TLB flushes,

				 * so no need to propagate the tlb argument.

				 */

				int nr_ptes = change_huge_pmd(tlb, vma, pmd,

				ret = change_huge_pmd(tlb, vma, pmd,

						addr, newprot, cp_flags);



				if (nr_ptes) {

					if (nr_ptes == HPAGE_PMD_NR) {

				if (ret) {

					if (ret == HPAGE_PMD_NR) {

						pages += HPAGE_PMD_NR;

						nr_huge_updates++;

					}
@@ -460,8 +416,12 @@ static inline long change_pmd_range(struct mmu_gather *tlb, 
			}

			/* fall through, the trans huge pmd just split */

		}

		pages += change_pte_range(tlb, vma, pmd, addr, next,

					  newprot, cp_flags);



		ret = change_pte_range(tlb, vma, pmd, addr, next, newprot,

				       cp_flags);

		if (ret < 0)

			goto again;

		pages += ret;

next:

		cond_resched();

	} while (pmd++, addr = next, addr != end);