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[172.10.233.147]) by smtp.gmail.com with ESMTPSA id 46e09a7af769-724ecdecdc1sm2462473a34.36.2025.01.27.12.55.23 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 27 Jan 2025 12:55:23 -0800 (PST) Date: Mon, 27 Jan 2025 12:55:11 -0800 (PST) From: Hugh Dickins To: Roman Gushchin cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Andrew Morton , Jann Horn , Peter Zijlstra , Will Deacon , "Aneesh Kumar K.V" , Nick Piggin , Hugh Dickins , linux-arch@vger.kernel.org Subject: Re: [PATCH v4] mmu_gather: move tlb flush for VM_PFNMAP/VM_MIXEDMAP vmas into free_pgtables() In-Reply-To: <20250127195321.35779-1-roman.gushchin@linux.dev> Message-ID: <61e3ea6a-368a-640f-a050-b56c8d3232b5@google.com> References: <20250127195321.35779-1-roman.gushchin@linux.dev> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII On Mon, 27 Jan 2025, Roman Gushchin wrote: > Commit b67fbebd4cf9 ("mmu_gather: Force tlb-flush VM_PFNMAP vmas") > added a forced tlbflush to tlb_vma_end(), which is required to avoid a > race between munmap() and unmap_mapping_range(). However it added some > overhead to other paths where tlb_vma_end() is used, but vmas are not > removed, e.g. madvise(MADV_DONTNEED). > > Fix this by moving the tlb flush out of tlb_end_vma() into > free_pgtables(), somewhat similar to the stable version of the > original commit: e.g. stable commit 895428ee124a ("mm: Force TLB flush > for PFNMAP mappings before unlink_file_vma()"). > > Note, that if tlb->fullmm is set, no flush is required, as the whole > mm is about to be destroyed. > > Signed-off-by: Roman Gushchin > Cc: Jann Horn > Cc: Peter Zijlstra > Cc: Will Deacon > Cc: "Aneesh Kumar K.V" > Cc: Andrew Morton > Cc: Nick Piggin > Cc: Hugh Dickins > Cc: linux-arch@vger.kernel.org > Cc: linux-mm@kvack.org > > --- > > v4: > - naming/comments update (by Peter Z.) > - check vma->vma->vm_flags in tlb_free_vma() (by Peter Z.) Let me just put on record: you were absolutely right not to extend to this the Ack I gave to v3, this v4 is silly (tlb_free_vma() and its multiple calls, necessary only because of the unnecessary extra test); but I don't see it as doing any actual damage, so I'll stop short of NAKking it. Hugh