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authorAndrea Arcangeli <aarcange@redhat.com>2018-10-27 01:10:40 +0300
committerLinus Torvalds <torvalds@linux-foundation.org>2018-10-27 02:38:15 +0300
commit7066f0f933a1fd707bb38781866657769cff7efc (patch)
tree79fb72354932977e88ec6dbeb4adbc63403cad08 /mm/huge_memory.c
parentd7c3393413fe7e7dc54498ea200ea94742d61e18 (diff)
downloadlinux-7066f0f933a1fd707bb38781866657769cff7efc.tar.xz
mm: thp: fix mmu_notifier in migrate_misplaced_transhuge_page()
change_huge_pmd() after arming the numa/protnone pmd doesn't flush the TLB right away. do_huge_pmd_numa_page() flushes the TLB before calling migrate_misplaced_transhuge_page(). By the time do_huge_pmd_numa_page() runs some CPU could still access the page through the TLB. change_huge_pmd() before arming the numa/protnone transhuge pmd calls mmu_notifier_invalidate_range_start(). So there's no need of mmu_notifier_invalidate_range_start()/mmu_notifier_invalidate_range_only_end() sequence in migrate_misplaced_transhuge_page() too, because by the time migrate_misplaced_transhuge_page() runs, the pmd mapping has already been invalidated in the secondary MMUs. It has to or if a secondary MMU can still write to the page, the migrate_page_copy() would lose data. However an explicit mmu_notifier_invalidate_range() is needed before migrate_misplaced_transhuge_page() starts copying the data of the transhuge page or the below can happen for MMU notifier users sharing the primary MMU pagetables and only implementing ->invalidate_range: CPU0 CPU1 GPU sharing linux pagetables using only ->invalidate_range ----------- ------------ --------- GPU secondary MMU writes to the page mapped by the transhuge pmd change_pmd_range() mmu..._range_start() ->invalidate_range_start() noop change_huge_pmd() set_pmd_at(numa/protnone) pmd_unlock() do_huge_pmd_numa_page() CPU TLB flush globally (1) CPU cannot write to page migrate_misplaced_transhuge_page() GPU writes to the page... migrate_page_copy() ...GPU stops writing to the page CPU TLB flush (2) mmu..._range_end() (3) ->invalidate_range_stop() noop ->invalidate_range() GPU secondary MMU is invalidated and cannot write to the page anymore (too late) Just like we need a CPU TLB flush (1) because the TLB flush (2) arrives too late, we also need a mmu_notifier_invalidate_range() before calling migrate_misplaced_transhuge_page(), because the ->invalidate_range() in (3) also arrives too late. This requirement is the result of the lazy optimization in change_huge_pmd() that releases the pmd_lock without first flushing the TLB and without first calling mmu_notifier_invalidate_range(). Even converting the removed mmu_notifier_invalidate_range_only_end() into a mmu_notifier_invalidate_range_end() would not have been enough to fix this, because it run after migrate_page_copy(). After the hugepage data copy is done migrate_misplaced_transhuge_page() can proceed and call set_pmd_at without having to flush the TLB nor any secondary MMUs because the secondary MMU invalidate, just like the CPU TLB flush, has to happen before the migrate_page_copy() is called or it would be a bug in the first place (and it was for drivers using ->invalidate_range()). KVM is unaffected because it doesn't implement ->invalidate_range(). The standard PAGE_SIZEd migrate_misplaced_page is less accelerated and uses the generic migrate_pages which transitions the pte from numa/protnone to a migration entry in try_to_unmap_one() and flushes TLBs and all mmu notifiers there before copying the page. Link: http://lkml.kernel.org/r/20181013002430.698-3-aarcange@redhat.com Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Acked-by: Mel Gorman <mgorman@suse.de> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Reviewed-by: Aaron Tomlin <atomlin@redhat.com> Cc: Jerome Glisse <jglisse@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/huge_memory.c')
-rw-r--r--mm/huge_memory.c14
1 files changed, 13 insertions, 1 deletions
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 25c7d7509cf4..25ef59b7ee34 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1558,8 +1558,20 @@ vm_fault_t do_huge_pmd_numa_page(struct vm_fault *vmf, pmd_t pmd)
* We are not sure a pending tlb flush here is for a huge page
* mapping or not. Hence use the tlb range variant
*/
- if (mm_tlb_flush_pending(vma->vm_mm))
+ if (mm_tlb_flush_pending(vma->vm_mm)) {
flush_tlb_range(vma, haddr, haddr + HPAGE_PMD_SIZE);
+ /*
+ * change_huge_pmd() released the pmd lock before
+ * invalidating the secondary MMUs sharing the primary
+ * MMU pagetables (with ->invalidate_range()). The
+ * mmu_notifier_invalidate_range_end() (which
+ * internally calls ->invalidate_range()) in
+ * change_pmd_range() will run after us, so we can't
+ * rely on it here and we need an explicit invalidate.
+ */
+ mmu_notifier_invalidate_range(vma->vm_mm, haddr,
+ haddr + HPAGE_PMD_SIZE);
+ }
/*
* Migrate the THP to the requested node, returns with page unlocked