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Commit cee216a6 authored by Aneesh Kumar K.V's avatar Aneesh Kumar K.V Committed by Linus Torvalds
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mm/autonuma: don't use set_pte_at when updating protnone ptes 

Architectures like ppc64, use privilege access bit to mark pte non
accessible.  This implies that kernel can do a copy_to_user to an
address marked for numa fault.  This also implies that there can be a
parallel hardware update for the pte.  set_pte_at cannot be used in such
scenarios.  Hence switch the pte update to use ptep_get_and_clear and
set_pte_at combination.

[akpm@linux-foundation.org: remove unwanted ppc change, per Aneesh]
Link: http://lkml.kernel.org/r/1486400776-28114-1-git-send-email-aneesh.kumar@linux.vnet.ibm.com


Signed-off-by: default avatarAneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Acked-by: default avatarRik van Riel <riel@redhat.com>
Acked-by: default avatarMel Gorman <mgorman@techsingularity.net>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 3f472cc9

mm/memory.c

+9 −9
Original line number Diff line number Diff line
@@ -3400,32 +3400,32 @@ static int do_numa_page(struct vm_fault *vmf) 
	int last_cpupid;

	int target_nid;

	bool migrated = false;

	pte_t pte = vmf->orig_pte;

	bool was_writable = pte_write(pte);

	pte_t pte;

	bool was_writable = pte_write(vmf->orig_pte);

	int flags = 0;



	/*

	 * The "pte" at this point cannot be used safely without

	 * validation through pte_unmap_same(). It's of NUMA type but

	 * the pfn may be screwed if the read is non atomic.

	 *

	 * We can safely just do a "set_pte_at()", because the old

	 * page table entry is not accessible, so there would be no

	 * concurrent hardware modifications to the PTE.

	 */

	vmf->ptl = pte_lockptr(vma->vm_mm, vmf->pmd);

	spin_lock(vmf->ptl);

	if (unlikely(!pte_same(*vmf->pte, pte))) {

	if (unlikely(!pte_same(*vmf->pte, vmf->orig_pte))) {

		pte_unmap_unlock(vmf->pte, vmf->ptl);

		goto out;

	}



	/* Make it present again */

	/*

	 * Make it present again, Depending on how arch implementes non

	 * accessible ptes, some can allow access by kernel mode.

	 */

	pte = ptep_modify_prot_start(vma->vm_mm, vmf->address, vmf->pte);

	pte = pte_modify(pte, vma->vm_page_prot);

	pte = pte_mkyoung(pte);

	if (was_writable)

		pte = pte_mkwrite(pte);

	set_pte_at(vma->vm_mm, vmf->address, vmf->pte, pte);

	ptep_modify_prot_commit(vma->vm_mm, vmf->address, vmf->pte, pte);

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



	page = vm_normal_page(vma, vmf->address, pte);