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Fri, 22 Aug 2025 07:12:00 -0700 (PDT) Message-ID: <98191ca5-9581-44fd-b9b1-6f0b932f141e@gmail.com> Date: Fri, 22 Aug 2025 18:11:58 +0400 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird To: torvalds@linux-foundation.org Cc: akpm@linux-foundation.org, andrealmeid@igalia.com, brauner@kernel.org, christophe.leroy@csgroup.eu, daniel@iogearbox.net, dave.hansen@linux.intel.com, dave@stgolabs.net, david.laight.linux@gmail.com, dvhart@infradead.org, jack@suse.cz, linux-block@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linuxppc-dev@lists.ozlabs.org, maddy@linux.ibm.com, mingo@redhat.com, mpe@ellerman.id.au, npiggin@gmail.com, peterz@infradead.org, tglx@linutronix.de, viro@zeniv.linux.org.uk References: Subject: Re: [PATCH v2 02/10] uaccess: Add speculation barrier to copy_from_user_iter() Content-Language: en-US From: Giorgi Tchankvetadze In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 1BFEF2000D X-Stat-Signature: sjund11g3dckyxjsxp1xd6k74cn418bm X-Rspam-User: X-HE-Tag: 1755871922-591510 X-HE-Meta: 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 /G1bmrlF S/Cew8uMb24/OVGXQNYLuKp4BmGTn7+xpdl4oewKOopPwcJW2ngYjNYhs+hvDixKUoTc4pzSNiDT//HULnzaJDEGxyzvom5d/X5KJw5GY3cbWGvRxLAGuYB95YS55wIES6New+Xw/nkggaTYESarr7lVSSjiAULhkm5PcQde54tHISis= 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: List-Subscribe: List-Unsubscribe: so we can use speculation barrier? and fix the problem locally On 8/22/2025 5:52 PM, Linus Torvalds wrote: > On Fri, 22 Aug 2025 at 05:58, Christophe Leroy > wrote: >> > The results of "access_ok()" can be mis-speculated. The result is > that > you can end speculatively: > > if (access_ok(from, size)) > // > Right here > I actually think that we should probably just make access_ok() itself do this. > > We don't have *that* many users since we have been de-emphasizing the > "check ahead of time" model, and any that are performance-critical can > these days be turned into masked addresses. > > As it is, now we're in the situation that careful places - like > _inline_copy_from_user(), and with your patch copy_from_user_iter() - > do maybe wethis by hand and are ugly as a result, and lazy and > probably incorrect places don't do it at all. > > That said, I don't object to this patch and maybe we should do that > access_ok() change later and independently of any powerpc work. > > Linus >