Re: [PATCH V3] powerpc/thp: Serialize pmd clear against a linux page table walk.
"Kirill A. Shutemov" writes: > On Mon, May 11, 2015 at 11:56:01AM +0530, Aneesh Kumar K.V wrote: >> Serialize against find_linux_pte_or_hugepte which does lock-less >> lookup in page tables with local interrupts disabled. For huge pages >> it casts pmd_t to pte_t. Since format of pte_t is different from >> pmd_t we want to prevent transit from pmd pointing to page table >> to pmd pointing to huge page (and back) while interrupts are disabled. >> We clear pmd to possibly replace it with page table pointer in >> different code paths. So make sure we wait for the parallel >> find_linux_pte_or_hugepage to finish. >> >> Without this patch, a find_linux_pte_or_hugepte running in parallel to >> __split_huge_zero_page_pmd or do_huge_pmd_wp_page_fallback or zap_huge_pmd >> can run into the above issue. With __split_huge_zero_page_pmd and >> do_huge_pmd_wp_page_fallback we clear the hugepage pte before inserting >> the pmd entry with a regular pgtable address. Such a clear need to >> wait for the parallel find_linux_pte_or_hugepte to finish. >> >> With zap_huge_pmd, we can run into issues, with a hugepage pte >> getting zapped due to a MADV_DONTNEED while other cpu fault it >> in as small pages. >> >> Reported-by: Kirill A. Shutemov >> Signed-off-by: Aneesh Kumar K.V > > Reviewed-by: Kirill A. Shutemov > > CC: stable@ ? Yes, We also need to pick, dac5657067919161eb3273ca787d8ae9814801e7 691e95fd7396905a38d98919e9c150dbc3ea21a3 7d6e7f7ffaba4e013c7a0589140431799bc17985 But that may need me to a backport, because we have dependencies in kvm and a cherry-pick may not work. Will work with Michael Ellerman to find out what needs to be done. -aneesh ___ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
Re: [PATCH V3] powerpc/thp: Serialize pmd clear against a linux page table walk.
On Mon, May 11, 2015 at 11:56:01AM +0530, Aneesh Kumar K.V wrote: > Serialize against find_linux_pte_or_hugepte which does lock-less > lookup in page tables with local interrupts disabled. For huge pages > it casts pmd_t to pte_t. Since format of pte_t is different from > pmd_t we want to prevent transit from pmd pointing to page table > to pmd pointing to huge page (and back) while interrupts are disabled. > We clear pmd to possibly replace it with page table pointer in > different code paths. So make sure we wait for the parallel > find_linux_pte_or_hugepage to finish. > > Without this patch, a find_linux_pte_or_hugepte running in parallel to > __split_huge_zero_page_pmd or do_huge_pmd_wp_page_fallback or zap_huge_pmd > can run into the above issue. With __split_huge_zero_page_pmd and > do_huge_pmd_wp_page_fallback we clear the hugepage pte before inserting > the pmd entry with a regular pgtable address. Such a clear need to > wait for the parallel find_linux_pte_or_hugepte to finish. > > With zap_huge_pmd, we can run into issues, with a hugepage pte > getting zapped due to a MADV_DONTNEED while other cpu fault it > in as small pages. > > Reported-by: Kirill A. Shutemov > Signed-off-by: Aneesh Kumar K.V Reviewed-by: Kirill A. Shutemov CC: stable@ ? -- Kirill A. Shutemov ___ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
[PATCH V3] powerpc/thp: Serialize pmd clear against a linux page table walk.
Serialize against find_linux_pte_or_hugepte which does lock-less lookup in page tables with local interrupts disabled. For huge pages it casts pmd_t to pte_t. Since format of pte_t is different from pmd_t we want to prevent transit from pmd pointing to page table to pmd pointing to huge page (and back) while interrupts are disabled. We clear pmd to possibly replace it with page table pointer in different code paths. So make sure we wait for the parallel find_linux_pte_or_hugepage to finish. Without this patch, a find_linux_pte_or_hugepte running in parallel to __split_huge_zero_page_pmd or do_huge_pmd_wp_page_fallback or zap_huge_pmd can run into the above issue. With __split_huge_zero_page_pmd and do_huge_pmd_wp_page_fallback we clear the hugepage pte before inserting the pmd entry with a regular pgtable address. Such a clear need to wait for the parallel find_linux_pte_or_hugepte to finish. With zap_huge_pmd, we can run into issues, with a hugepage pte getting zapped due to a MADV_DONTNEED while other cpu fault it in as small pages. Reported-by: Kirill A. Shutemov Signed-off-by: Aneesh Kumar K.V --- Changes from V2: * Drop the cleanup patch Will this as a separate patch and not bug fix. * Update commit message arch/powerpc/mm/pgtable_64.c | 11 +++ 1 file changed, 11 insertions(+) diff --git a/arch/powerpc/mm/pgtable_64.c b/arch/powerpc/mm/pgtable_64.c index b651179ac4da..1325be89e670 100644 --- a/arch/powerpc/mm/pgtable_64.c +++ b/arch/powerpc/mm/pgtable_64.c @@ -845,6 +845,17 @@ pmd_t pmdp_get_and_clear(struct mm_struct *mm, * hash fault look at them. */ memset(pgtable, 0, PTE_FRAG_SIZE); + /* +* Serialize against find_linux_pte_or_hugepte which does lock-less +* lookup in page tables with local interrupts disabled. For huge pages +* it casts pmd_t to pte_t. Since format of pte_t is different from +* pmd_t we want to prevent transit from pmd pointing to page table +* to pmd pointing to huge page (and back) while interrupts are disabled. +* We clear pmd to possibly replace it with page table pointer in +* different code paths. So make sure we wait for the parallel +* find_linux_pte_or_hugepage to finish. +*/ + kick_all_cpus_sync(); return old_pmd; } -- 2.1.4 ___ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev