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[82.69.66.36]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-49e7ef24be2sm30342585e9.0.2026.09.15.01.43.40 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 15 Sep 2026 01:43:41 -0700 (PDT) Date: Tue, 15 Sep 2026 09:43:39 +0100 From: David Laight To: Borislav Petkov Cc: Mauricio Faria de Oliveira , Thomas Gleixner , Ingo Molnar , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , Juergen Gross , Alexey Dobriyan , Boris Ostrovsky , Jan Beulich , Brian Gerst , kernel-dev@igalia.com, linux-kernel@vger.kernel.org, xen-devel@lists.xenproject.org Subject: Re: [PATCH v9 4/5] x86/cpuid: fix unbootable VMs by really inlining memcmp() in hypervisor_cpuid_base() Message-ID: <20260915094339.39a83b54@pumpkin> In-Reply-To: <20260915051155.GGaqjTm7yIluwxZ80x@fat_crate.local> References: <20260822-pvh-kasan-inline-v9-0-e70ef3b75b6a@igalia.com> <20260822-pvh-kasan-inline-v9-4-e70ef3b75b6a@igalia.com> <20260911043822.GHaqOFvnw5mQ0s89QQ@fat_crate.local> <6113f06c790cfe1141d2dc09b68937b6@igalia.com> <20260915051155.GGaqjTm7yIluwxZ80x@fat_crate.local> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; arm-unknown-linux-gnueabihf) 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 Content-Transfer-Encoding: 7bit On Mon, 14 Sep 2026 22:11:55 -0700 Borislav Petkov wrote: > On Mon, Sep 14, 2026 at 08:22:08AM -0300, Mauricio Faria de Oliveira wrote: > > In the review of the original patchset (fixed by this series) it is > > mentioned that a compiler might turn it into a memcmp() [1] -- and thus > > revert back to the same issue. > > > > [1] https://lore.kernel.org/all/877ccz12ab.ffs@tglx/ > > Hmm, never heard that before but that doesn't mean anything. Probably should > mention it in one of the commit messages so that we know for the future... > It definitely has a habit of converting copy loops to memcpy(). Annoying when they are short. But usually easily avoidable by sprinkling 'volatile' or barrier() in the right places. David