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Commit a4e72cb7 authored by Laurent Dufour's avatar Laurent Dufour Committed by Gerrit - the friendly Code Review server
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mm: introduce __page_add_new_anon_rmap() 



When dealing with speculative page fault handler, we may race with VMA
being split or merged. In this case the vma->vm_start and vm->vm_end
fields may not match the address the page fault is occurring.

This can only happens when the VMA is split but in that case, the
anon_vma pointer of the new VMA will be the same as the original one,
because in __split_vma the new->anon_vma is set to src->anon_vma when
*new = *vma.

So even if the VMA boundaries are not correct, the anon_vma pointer is
still valid.

If the VMA has been merged, then the VMA in which it has been merged
must have the same anon_vma pointer otherwise the merge can't be done.

So in all the case we know that the anon_vma is valid, since we have
checked before starting the speculative page fault that the anon_vma
pointer is valid for this VMA and since there is an anon_vma this
means that at one time a page has been backed and that before the VMA
is cleaned, the page table lock would have to be grab to clean the
PTE, and the anon_vma field is checked once the PTE is locked.

This patch introduce a new __page_add_new_anon_rmap() service which
doesn't check for the VMA boundaries, and create a new inline one
which do the check.

When called from a page fault handler, if this is not a speculative one,
there is a guarantee that vm_start and vm_end match the faulting address,
so this check is useless. In the context of the speculative page fault
handler, this check may be wrong but anon_vma is still valid as explained
above.

Change-Id: I72c47830181579f8c9618df879077d321653b5f1
Signed-off-by: default avatarLaurent Dufour <ldufour@linux.vnet.ibm.com>
Patch-mainline: linux-mm @ Tue, 17 Apr 2018 16:33:22
[vinmenon@codeaurora.org: trivial merge conflict fixes +
checkpatch fixes]
Signed-off-by: default avatarVinayak Menon <vinmenon@codeaurora.org>
parent d3061f2e

include/linux/rmap.h

+10 −2
Original line number Diff line number Diff line
@@ -174,8 +174,16 @@ void page_add_anon_rmap(struct page *, struct vm_area_struct *, 
		unsigned long, bool);

void do_page_add_anon_rmap(struct page *, struct vm_area_struct *,

			   unsigned long, int);

void page_add_new_anon_rmap(struct page *, struct vm_area_struct *,

		unsigned long, bool);

void __page_add_new_anon_rmap(struct page *page, struct vm_area_struct *vma,

			      unsigned long address, bool compound);

static inline void page_add_new_anon_rmap(struct page *page,

					  struct vm_area_struct *vma,

					  unsigned long address, bool compound)

{

	VM_BUG_ON_VMA(address < vma->vm_start || address >= vma->vm_end, vma);

	__page_add_new_anon_rmap(page, vma, address, compound);

}



void page_add_file_rmap(struct page *, bool);

void page_remove_rmap(struct page *, bool);

mm/memory.c

+4 −4
Original line number Diff line number Diff line
@@ -2580,7 +2580,7 @@ static vm_fault_t wp_page_copy(struct vm_fault *vmf) 
		 * thread doing COW.

		 */

		ptep_clear_flush_notify(vma, vmf->address, vmf->pte);

		page_add_new_anon_rmap(new_page, vma, vmf->address, false);

		__page_add_new_anon_rmap(new_page, vma, vmf->address, false);

		mem_cgroup_commit_charge(new_page, memcg, false, false);

		__lru_cache_add_active_or_unevictable(new_page, vmf->vma_flags);

		/*
@@ -3119,7 +3119,7 @@ vm_fault_t do_swap_page(struct vm_fault *vmf) 


	/* ksm created a completely new copy */

	if (unlikely(page != swapcache && swapcache)) {

		page_add_new_anon_rmap(page, vma, vmf->address, false);

		__page_add_new_anon_rmap(page, vma, vmf->address, false);

		mem_cgroup_commit_charge(page, memcg, false, false);

		__lru_cache_add_active_or_unevictable(page, vmf->vma_flags);

	} else {
@@ -3270,7 +3270,7 @@ static vm_fault_t do_anonymous_page(struct vm_fault *vmf) 
	}



	inc_mm_counter_fast(vma->vm_mm, MM_ANONPAGES);

	page_add_new_anon_rmap(page, vma, vmf->address, false);

	__page_add_new_anon_rmap(page, vma, vmf->address, false);

	mem_cgroup_commit_charge(page, memcg, false, false);

	__lru_cache_add_active_or_unevictable(page, vmf->vma_flags);

setpte:
@@ -3552,7 +3552,7 @@ vm_fault_t alloc_set_pte(struct vm_fault *vmf, struct mem_cgroup *memcg, 
	/* copy-on-write page */

	if (write && !(vmf->vma_flags & VM_SHARED)) {

		inc_mm_counter_fast(vma->vm_mm, MM_ANONPAGES);

		page_add_new_anon_rmap(page, vma, vmf->address, false);

		__page_add_new_anon_rmap(page, vma, vmf->address, false);

		mem_cgroup_commit_charge(page, memcg, false, false);

		__lru_cache_add_active_or_unevictable(page, vmf->vma_flags);

	} else {

mm/rmap.c

+2 −3
Original line number Diff line number Diff line
@@ -1137,7 +1137,7 @@ void do_page_add_anon_rmap(struct page *page, 
}



/**

 * page_add_new_anon_rmap - add pte mapping to a new anonymous page

 * __page_add_new_anon_rmap - add pte mapping to a new anonymous page

 * @page:	the page to add the mapping to

 * @vma:	the vm area in which the mapping is added

 * @address:	the user virtual address mapped
@@ -1147,12 +1147,11 @@ void do_page_add_anon_rmap(struct page *page, 
 * This means the inc-and-test can be bypassed.

 * Page does not have to be locked.

 */

void page_add_new_anon_rmap(struct page *page,

void __page_add_new_anon_rmap(struct page *page,

	struct vm_area_struct *vma, unsigned long address, bool compound)

{

	int nr = compound ? hpage_nr_pages(page) : 1;



	VM_BUG_ON_VMA(address < vma->vm_start || address >= vma->vm_end, vma);

	__SetPageSwapBacked(page);

	if (compound) {

		VM_BUG_ON_PAGE(!PageTransHuge(page), page);