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.
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxxxxxxx>
---
arch/powerpc/mm/pgtable.c | 7 +------
mm/memory.c | 18 +++++++++---------
2 files changed, 10 insertions(+), 15 deletions(-)
diff --git a/arch/powerpc/mm/pgtable.c b/arch/powerpc/mm/pgtable.c
index cb39c8bd2436..b8ac81a16389 100644
--- a/arch/powerpc/mm/pgtable.c
+++ b/arch/powerpc/mm/pgtable.c
@@ -186,12 +186,7 @@ static pte_t set_access_flags_filter(pte_t pte, struct vm_area_struct *vma,
void set_pte_at(struct mm_struct *mm, unsigned long addr, pte_t *ptep,
pte_t pte)
{
- /*
- * When handling numa faults, we already have the pte marked
- * _PAGE_PRESENT, but we can be sure that it is not in hpte.
- * Hence we can use set_pte_at for them.
- */
- VM_WARN_ON(pte_present(*ptep) && !pte_protnone(*ptep));
+ VM_WARN_ON(pte_present(*ptep));
/*
* Add the pte bit when tryint set a pte
diff --git a/mm/memory.c b/mm/memory.c
index 6bf2b471e30c..e78bf72f30dd 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3387,32 +3387,32 @@ 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);
--
2.7.4
--
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