diff options
Diffstat (limited to '')
| -rw-r--r-- | mm/huge_memory.c | 72 |
1 files changed, 35 insertions, 37 deletions
diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 2a79a6b7d19b..87ab9b8f56b5 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -2063,7 +2063,7 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd, struct mm_struct *mm = vma->vm_mm; struct page *page; pgtable_t pgtable; - pmd_t old, _pmd; + pmd_t old_pmd, _pmd; bool young, write, soft_dirty, pmd_migration = false; unsigned long addr; int i; @@ -2106,23 +2106,50 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd, return __split_huge_zero_page_pmd(vma, haddr, pmd); } + /* + * Up to this point the pmd is present and huge and userland has the + * whole access to the hugepage during the split (which happens in + * place). If we overwrite the pmd with the not-huge version pointing + * to the pte here (which of course we could if all CPUs were bug + * free), userland could trigger a small page size TLB miss on the + * small sized TLB while the hugepage TLB entry is still established in + * the huge TLB. Some CPU doesn't like that. + * See http://support.amd.com/us/Processor_TechDocs/41322.pdf, Erratum + * 383 on page 93. Intel should be safe but is also warns that it's + * only safe if the permission and cache attributes of the two entries + * loaded in the two TLB is identical (which should be the case here). + * But it is generally safer to never allow small and huge TLB entries + * for the same virtual address to be loaded simultaneously. So instead + * of doing "pmd_populate(); flush_pmd_tlb_range();" we first mark the + * current pmd notpresent (atomically because here the pmd_trans_huge + * must remain set at all times on the pmd until the split is complete + * for this pmd), then we flush the SMP TLB and finally we write the + * non-huge version of the pmd entry with pmd_populate. + */ + old_pmd = pmdp_invalidate(vma, haddr, pmd); + #ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION - pmd_migration = is_pmd_migration_entry(*pmd); + pmd_migration = is_pmd_migration_entry(old_pmd); if (pmd_migration) { swp_entry_t entry; - entry = pmd_to_swp_entry(*pmd); + entry = pmd_to_swp_entry(old_pmd); page = pfn_to_page(swp_offset(entry)); } else #endif - page = pmd_page(*pmd); + page = pmd_page(old_pmd); VM_BUG_ON_PAGE(!page_count(page), page); page_ref_add(page, HPAGE_PMD_NR - 1); - write = pmd_write(*pmd); - young = pmd_young(*pmd); - soft_dirty = pmd_soft_dirty(*pmd); + if (pmd_dirty(old_pmd)) + SetPageDirty(page); + write = pmd_write(old_pmd); + young = pmd_young(old_pmd); + soft_dirty = pmd_soft_dirty(old_pmd); - pmdp_huge_split_prepare(vma, haddr, pmd); + /* + * Withdraw the table only after we mark the pmd entry invalid. + * This's critical for some architectures (Power). + */ pgtable = pgtable_trans_huge_withdraw(mm, pmd); pmd_populate(mm, &_pmd, pgtable); @@ -2176,35 +2203,6 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd, } smp_wmb(); /* make pte visible before pmd */ - /* - * Up to this point the pmd is present and huge and userland has the - * whole access to the hugepage during the split (which happens in - * place). If we overwrite the pmd with the not-huge version pointing - * to the pte here (which of course we could if all CPUs were bug - * free), userland could trigger a small page size TLB miss on the - * small sized TLB while the hugepage TLB entry is still established in - * the huge TLB. Some CPU doesn't like that. - * See http://support.amd.com/us/Processor_TechDocs/41322.pdf, Erratum - * 383 on page 93. Intel should be safe but is also warns that it's - * only safe if the permission and cache attributes of the two entries - * loaded in the two TLB is identical (which should be the case here). - * But it is generally safer to never allow small and huge TLB entries - * for the same virtual address to be loaded simultaneously. So instead - * of doing "pmd_populate(); flush_pmd_tlb_range();" we first mark the - * current pmd notpresent (atomically because here the pmd_trans_huge - * must remain set at all times on the pmd until the split is complete - * for this pmd), then we flush the SMP TLB and finally we write the - * non-huge version of the pmd entry with pmd_populate. - */ - old = pmdp_invalidate(vma, haddr, pmd); - - /* - * Transfer dirty bit using value returned by pmd_invalidate() to be - * sure we don't race with CPU that can set the bit under us. - */ - if (pmd_dirty(old)) - SetPageDirty(page); - pmd_populate(mm, pmd, pgtable); if (freeze) { |