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Thu, 12 Sep 2024 02:30:17 -0700 (PDT) Received: from [10.4.59.158] ([139.177.225.242]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-2db043c0672sm9995203a91.22.2024.09.12.02.30.10 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 12 Sep 2024 02:30:16 -0700 (PDT) Message-ID: <7782bc62-a09f-465a-aa43-8179542ecc02@bytedance.com> Date: Thu, 12 Sep 2024 17:30:10 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 10/14] mm: page_vma_mapped_walk: map_pte() use pte_offset_map_rw_nolock() Content-Language: en-US To: Muchun Song Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, david@redhat.com, hughd@google.com, willy@infradead.org, vbabka@kernel.org, akpm@linux-foundation.org, rppt@kernel.org, vishal.moola@gmail.com, peterx@redhat.com, ryan.roberts@arm.com, christophe.leroy2@cs-soprasteria.com References: <20240904084022.32728-1-zhengqi.arch@bytedance.com> <20240904084022.32728-11-zhengqi.arch@bytedance.com> From: Qi Zheng In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 2024/9/5 20:07, Muchun Song wrote: > > > On 2024/9/4 16:40, Qi Zheng wrote: >> In the caller of map_pte(), we may modify the pvmw->pte after acquiring >> the pvmw->ptl, so convert it to using pte_offset_map_rw_nolock(). At >> this time, the pte_same() check is not performed after the pvmw->ptl >> held, >> so we should get pmdval and do pmd_same() check to ensure the >> stability of >> pvmw->pmd. >> >> Signed-off-by: Qi Zheng >> --- >>   mm/page_vma_mapped.c | 24 ++++++++++++++++++++---- >>   1 file changed, 20 insertions(+), 4 deletions(-) >> >> diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c >> index ae5cc42aa2087..f1d73fd448708 100644 >> --- a/mm/page_vma_mapped.c >> +++ b/mm/page_vma_mapped.c >> @@ -13,9 +13,11 @@ static inline bool not_found(struct >> page_vma_mapped_walk *pvmw) >>       return false; >>   } >> -static bool map_pte(struct page_vma_mapped_walk *pvmw, spinlock_t >> **ptlp) >> +static bool map_pte(struct page_vma_mapped_walk *pvmw, pmd_t *pmdvalp, >> +            spinlock_t **ptlp) >>   { >>       pte_t ptent; >> +    pmd_t pmdval; >>       if (pvmw->flags & PVMW_SYNC) { >>           /* Use the stricter lookup */ >> @@ -25,6 +27,7 @@ static bool map_pte(struct page_vma_mapped_walk >> *pvmw, spinlock_t **ptlp) >>           return !!pvmw->pte; >>       } >> +again: >>       /* >>        * It is important to return the ptl corresponding to pte, >>        * in case *pvmw->pmd changes underneath us; so we need to >> @@ -32,10 +35,11 @@ static bool map_pte(struct page_vma_mapped_walk >> *pvmw, spinlock_t **ptlp) >>        * proceeds to loop over next ptes, and finds a match later. >>        * Though, in most cases, page lock already protects this. >>        */ >> -    pvmw->pte = pte_offset_map_nolock(pvmw->vma->vm_mm, pvmw->pmd, >> -                      pvmw->address, ptlp); >> +    pvmw->pte = pte_offset_map_rw_nolock(pvmw->vma->vm_mm, pvmw->pmd, >> +                         pvmw->address, &pmdval, ptlp); >>       if (!pvmw->pte) >>           return false; >> +    *pmdvalp = pmdval; >>       ptent = ptep_get(pvmw->pte); >> @@ -69,6 +73,12 @@ static bool map_pte(struct page_vma_mapped_walk >> *pvmw, spinlock_t **ptlp) >>       } >>       pvmw->ptl = *ptlp; >>       spin_lock(pvmw->ptl); >> + >> +    if (unlikely(!pmd_same(pmdval, pmdp_get_lockless(pvmw->pmd)))) { >> +        spin_unlock(pvmw->ptl); > > Forgot to clear pvmw->ptl? Or how about moving the assignment for it > to the place where the pmd_same check is successful? > >> +        goto again; >> +    } >> + > > Maybe here is the right place to assign pvmw->ptl. Right, will do in the v4. > > Muchun, > Thanks. > >>       return true; >>   } >> @@ -278,7 +288,7 @@ bool page_vma_mapped_walk(struct >> page_vma_mapped_walk *pvmw) >>               step_forward(pvmw, PMD_SIZE); >>               continue; >>           } >> -        if (!map_pte(pvmw, &ptl)) { >> +        if (!map_pte(pvmw, &pmde, &ptl)) { >>               if (!pvmw->pte) >>                   goto restart; >>               goto next_pte; >> @@ -307,6 +317,12 @@ bool page_vma_mapped_walk(struct >> page_vma_mapped_walk *pvmw) >>           if (!pvmw->ptl) { >>               pvmw->ptl = ptl; >>               spin_lock(pvmw->ptl); >> +            if (unlikely(!pmd_same(pmde, >> pmdp_get_lockless(pvmw->pmd)))) { >> +                pte_unmap_unlock(pvmw->pte, pvmw->ptl); >> +                pvmw->ptl = NULL; >> +                pvmw->pte = NULL; >> +                goto restart; >> +            } >>           } >>           goto this_pte; >>       } while (pvmw->address < end); >