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t=1683505823; bh=Ku2BCycuOdBG80SFOKA5kbRxCQtR2qKfQc50CpXVufY=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=eZIllEHhRUrFIWI47sBt/vsXJlLqnQOnLiEdORTmPnuZQaSEmSXnXdZrOCyDODQ46 2xTIkzO5J+It+eCoWaNMYurOO0oSV2L1qfxW6YOsO6lWwyMdRrMfB8vVZFfwEA/hkY WT5ednNEx2Fvqk3X8c9uTz/FSpYGscShWmEGShPY= Date: Sun, 7 May 2023 17:30:22 -0700 From: Andrew Morton To: Lorenzo Stoakes Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, David Hildenbrand Subject: Re: [PATCH] mm/gup: add missing gup_must_unshare() check to gup_huge_pgd() Message-Id: <20230507173022.96c9d24cb1aa6f57ed50f5fa@linux-foundation.org> In-Reply-To: References: X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Stat-Signature: s3optd9oaeig3371pmp5e9btad5nqfpx X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 3D584180009 X-Rspam-User: X-HE-Tag: 1683505824-265384 X-HE-Meta: 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 m7+BO/R9 Sno1Usfcpe5R4hAvD4xqKIfomA+dN/gMCGJcHAUXWsCKuWV7vSPT3nYICAX/MnEBJRTtI3ZYkEVhbAvBcDolQQxSxvgo7B21M0X1WtMjiDqOLjf/73oyjCOM4BOvXinzR2ar/hcVACL+KSMZDf06DYeT/sIJHmj2Tvf/CeoThhc19Tn22zo/gktgvJewRafsExlx2mP1fV1HnszVZTQyBhQ55W6om9Sc9b16XZLkRFtH/MrvQKZyiuKQn1bO/FBQxk7ndXK74T+1yC+w9MS6dpqB6d7+xs8EWSja1twqvCIF90UaYhM0Os/aX+KLhQMNJjL3rU6Ib58zj9vN8d4pOA9IhW0C0LZ2wZhTDP7yCfDyK+vYhet/G6soGv7Sk8lVmkVBjB3oSrF9/35s9vPgzm8vAn3lFq+mdeZij+2GHev3bLYklb8HTaddV2nrSxyIscZLy 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 Sat, 6 May 2023 15:05:25 +0100 Lorenzo Stoakes wrote: > All other instances of gup_huge_pXd() perform the unshare check, so update > the PGD-specific function to do so as well. > > While checking pgd_write() might seem unusual, this function already > performs such a check via pgd_access_permitted() so this is in line with > the existing implementation. Rationale seems strange. "Other sites do it so this should also". Why is this a desirable change? Maybe the "other instances" shouldn't be performing this check either? IOW, what are the runtime effects of this change? Thanks.