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: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Acked-by: Rik van Riel <riel@redhat.com>
Acked-by: Mel Gorman <mgorman@techsingularity.net>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/memory.c b/mm/memory.c
index bfad9fe316c1f0d305a80192dfcaea36068711b0..0c759ba122e12ec960e125023b90ec10ae771059 100644 (file)
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -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);