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AJvYcCX2kkv39O+2i2Z0OJqwS41vyetXPdN8NYRnGpuFbPXU76rtZRoJqDhNXNml3z+3Fsmt/xYCCrwzDtHwHCg=@vger.kernel.org X-Gm-Message-State: AOJu0Yyln0yo+ieRlDcBqERLo4d5pZ5Cxh+B4uQBWSVhM1dlP2zdyqXr A9mMcgj76ibpEjH2i1f5CcDYx5Rgx5Wx/KXCNmRjlia3M6jYkMpZQ9wkLfHkeXxYY0T4+SDAypU X X-Google-Smtp-Source: AGHT+IGA58OvjKH0J4J2cIX3fLSuJFJn0gN/GxxZsycyrte2t3fRU9GFiUDq/Yj/11t+E+u1iwSoVA== X-Received: by 2002:a17:90a:744d:b0:2d8:b075:7862 with SMTP id 98e67ed59e1d1-2dd7f380806mr18925374a91.5.1727166840378; Tue, 24 Sep 2024 01:34:00 -0700 (PDT) Received: from [10.68.125.128] ([63.216.146.178]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-2e058f2e2f5sm953563a91.24.2024.09.24.01.33.54 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 24 Sep 2024 01:33:59 -0700 (PDT) Message-ID: Date: Tue, 24 Sep 2024 16:33:52 +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 v4 10/13] mm: page_vma_mapped_walk: map_pte() use pte_offset_map_rw_nolock() Content-Language: en-US To: Muchun Song Cc: 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, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org References: From: Qi Zheng In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 2024/9/24 16:25, Muchun Song wrote: > > >> On Sep 24, 2024, at 14:11, 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 | 25 ++++++++++++++++++++----- >> 1 file changed, 20 insertions(+), 5 deletions(-) >> >> diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c >> index ae5cc42aa2087..6410f29b37c1b 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; > > Why declare a new variable? Can’t we use *pmdvalp instead? It's just a coding habit, both are fine for me. > >> >> 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); >> >> @@ -67,8 +71,13 @@ static bool map_pte(struct page_vma_mapped_walk *pvmw, spinlock_t **ptlp) >> } else if (!pte_present(ptent)) { >> return false; >> } >> + spin_lock(*ptlp); >> + if (unlikely(!pmd_same(pmdval, pmdp_get_lockless(pvmw->pmd)))) { >> + pte_unmap_unlock(pvmw->pte, *ptlp); >> + goto again; >> + } >> pvmw->ptl = *ptlp; >> - spin_lock(pvmw->ptl); >> + >> return true; >> } >> >> @@ -278,7 +287,7 @@ 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 +316,12 @@ 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); >> -- >> 2.20.1 >>