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Fri, 20 Nov 2020 08:03:23 -0800 (PST) Date: Fri, 20 Nov 2020 08:03:21 -0800 From: Minchan Kim To: Will Deacon Cc: linux-kernel@vger.kernel.org, kernel-team@android.com, Catalin Marinas , Yu Zhao , Peter Zijlstra , Linus Torvalds , Anshuman Khandual , linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, stable@vger.kernel.org Subject: Re: [PATCH 1/6] arm64: pgtable: Fix pte_accessible() Message-ID: <20201120160321.GB3377168@google.com> References: <20201120143557.6715-1-will@kernel.org> <20201120143557.6715-2-will@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201120143557.6715-2-will@kernel.org> X-Bogosity: Ham, tests=bogofilter, spamicity=0.000001, 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 02:35:52PM +0000, Will Deacon wrote: > pte_accessible() is used by ptep_clear_flush() to figure out whether TLB > invalidation is necessary when unmapping pages for reclaim. Although our > implementation is correct according to the architecture, returning true > only for valid, young ptes in the absence of racing page-table > modifications, this is in fact flawed due to lazy invalidation of old > ptes in ptep_clear_flush_young() where we elide the expensive DSB > instruction for completing the TLB invalidation. > > Rather than penalise the aging path, adjust pte_accessible() to return > true for any valid pte, even if the access flag is cleared. > > Cc: > Fixes: 76c714be0e5e ("arm64: pgtable: implement pte_accessible()") > Reported-by: Yu Zhao > Signed-off-by: Will Deacon Reviewed-by: Minchan Kim