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Fri, 20 Nov 2020 12:22:57 -0800 (PST) Date: Fri, 20 Nov 2020 13:22:53 -0700 From: Yu Zhao To: Will Deacon Cc: linux-kernel@vger.kernel.org, kernel-team@android.com, Catalin Marinas , Minchan Kim , Peter Zijlstra , Linus Torvalds , Anshuman Khandual , linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH 4/6] mm: proc: Invalidate TLB after clearing soft-dirty page state Message-ID: <20201120202253.GB1303870@google.com> References: <20201120143557.6715-1-will@kernel.org> <20201120143557.6715-5-will@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201120143557.6715-5-will@kernel.org> X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Fri, Nov 20, 2020 at 02:35:55PM +0000, Will Deacon wrote: > Since commit 0758cd830494 ("asm-generic/tlb: avoid potential double flush"), > TLB invalidation is elided in tlb_finish_mmu() if no entries were batched > via the tlb_remove_*() functions. Consequently, the page-table modifications > performed by clear_refs_write() in response to a write to > /proc//clear_refs do not perform TLB invalidation. Although this is > fine when simply aging the ptes, in the case of clearing the "soft-dirty" > state we can end up with entries where pte_write() is false, yet a > writable mapping remains in the TLB. I don't think we need a TLB flush in this context, same reason as we don't have one in copy_present_pte() which uses ptep_set_wrprotect() to write-protect a src PTE. ptep_modify_prot_start/commit() and ptep_set_wrprotect() guarantee either the dirty bit is set (when a PTE is still writable) or a PF happens (when a PTE has become r/o) when h/w page table walker races with kernel that modifies a PTE using the two APIs. > Fix this by calling tlb_remove_tlb_entry() for each entry being > write-protected when cleating soft-dirty. > > Signed-off-by: Will Deacon > --- > fs/proc/task_mmu.c | 18 +++++++++++------- > 1 file changed, 11 insertions(+), 7 deletions(-) > > diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c > index cd03ab9087b0..3308292ee5c5 100644 > --- a/fs/proc/task_mmu.c > +++ b/fs/proc/task_mmu.c > @@ -1032,11 +1032,12 @@ enum clear_refs_types { > > struct clear_refs_private { > enum clear_refs_types type; > + struct mmu_gather *tlb; > }; > > #ifdef CONFIG_MEM_SOFT_DIRTY > static inline void clear_soft_dirty(struct vm_area_struct *vma, > - unsigned long addr, pte_t *pte) > + unsigned long addr, pte_t *pte, struct mmu_gather *tlb) > { > /* > * The soft-dirty tracker uses #PF-s to catch writes > @@ -1053,6 +1054,7 @@ static inline void clear_soft_dirty(struct vm_area_struct *vma, > ptent = pte_wrprotect(old_pte); > ptent = pte_clear_soft_dirty(ptent); > ptep_modify_prot_commit(vma, addr, pte, old_pte, ptent); > + tlb_remove_tlb_entry(tlb, pte, addr); > } else if (is_swap_pte(ptent)) { > ptent = pte_swp_clear_soft_dirty(ptent); > set_pte_at(vma->vm_mm, addr, pte, ptent); > @@ -1060,14 +1062,14 @@ static inline void clear_soft_dirty(struct vm_area_struct *vma, > } > #else > static inline void clear_soft_dirty(struct vm_area_struct *vma, > - unsigned long addr, pte_t *pte) > + unsigned long addr, pte_t *pte, struct mmu_gather *tlb) > { > } > #endif > > #if defined(CONFIG_MEM_SOFT_DIRTY) && defined(CONFIG_TRANSPARENT_HUGEPAGE) > static inline void clear_soft_dirty_pmd(struct vm_area_struct *vma, > - unsigned long addr, pmd_t *pmdp) > + unsigned long addr, pmd_t *pmdp, struct mmu_gather *tlb) > { > pmd_t old, pmd = *pmdp; > > @@ -1081,6 +1083,7 @@ static inline void clear_soft_dirty_pmd(struct vm_area_struct *vma, > > pmd = pmd_wrprotect(pmd); > pmd = pmd_clear_soft_dirty(pmd); > + tlb_remove_pmd_tlb_entry(tlb, pmdp, addr); > > set_pmd_at(vma->vm_mm, addr, pmdp, pmd); > } else if (is_migration_entry(pmd_to_swp_entry(pmd))) { > @@ -1090,7 +1093,7 @@ static inline void clear_soft_dirty_pmd(struct vm_area_struct *vma, > } > #else > static inline void clear_soft_dirty_pmd(struct vm_area_struct *vma, > - unsigned long addr, pmd_t *pmdp) > + unsigned long addr, pmd_t *pmdp, struct mmu_gather *tlb) > { > } > #endif > @@ -1107,7 +1110,7 @@ static int clear_refs_pte_range(pmd_t *pmd, unsigned long addr, > ptl = pmd_trans_huge_lock(pmd, vma); > if (ptl) { > if (cp->type == CLEAR_REFS_SOFT_DIRTY) { > - clear_soft_dirty_pmd(vma, addr, pmd); > + clear_soft_dirty_pmd(vma, addr, pmd, cp->tlb); > goto out; > } > > @@ -1133,7 +1136,7 @@ static int clear_refs_pte_range(pmd_t *pmd, unsigned long addr, > ptent = *pte; > > if (cp->type == CLEAR_REFS_SOFT_DIRTY) { > - clear_soft_dirty(vma, addr, pte); > + clear_soft_dirty(vma, addr, pte, cp->tlb); > continue; > } > > @@ -1212,7 +1215,8 @@ static ssize_t clear_refs_write(struct file *file, const char __user *buf, > if (mm) { > struct mmu_notifier_range range; > struct clear_refs_private cp = { > - .type = type, > + .type = type, > + .tlb = &tlb, > }; > > if (type == CLEAR_REFS_MM_HIWATER_RSS) { > -- > 2.29.2.454.gaff20da3a2-goog >