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[82.69.66.36]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-429897f52aasm5709612f8f.12.2025.10.23.14.23.34 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 23 Oct 2025 14:23:35 -0700 (PDT) Date: Thu, 23 Oct 2025 22:23:33 +0100 From: David Laight To: Peter Zijlstra Cc: "Kaplan, David" , Thomas Gleixner , Borislav Petkov , Josh Poimboeuf , Pawan Gupta , Ingo Molnar , Dave Hansen , "x86@kernel.org" , "H . Peter Anvin" , Alexander Graf , Boris Ostrovsky , "linux-kernel@vger.kernel.org" Subject: Re: [RFC PATCH 40/56] x86/alternative: Use sync_core_nmi_safe() Message-ID: <20251023222333.4cac1430@pumpkin> In-Reply-To: <20251020150133.GK3245006@noisy.programming.kicks-ass.net> References: <20251013143444.3999-1-david.kaplan@amd.com> <20251013143444.3999-41-david.kaplan@amd.com> <20251016103549.GD3289052@noisy.programming.kicks-ass.net> <20251016144730.GC3245006@noisy.programming.kicks-ass.net> <20251020150133.GK3245006@noisy.programming.kicks-ass.net> 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, 20 Oct 2025 17:01:33 +0200 Peter Zijlstra wrote: > On Mon, Oct 20, 2025 at 02:49:56PM +0000, Kaplan, David wrote: > > > Coming back to this, are you thinking we should just create something > > like 'text_poke_sync_core()' inside alternative.c and that can use: > > 1. SERIALIZE (if available) > > 2. MOV-CR2 (if re-patching) > > 3. Else, IRET > > > > And maybe someday we put MFENCE into there too for AMD parts. > > > > Right now, of course this is the only logic that would care about an > > NMI-safe sync_core(). So maybe this makes sense vs creating a generic > > version that nobody else is using? > > I was thinking something fairly straight forward like the below. Yes, > there are a few more sync_core() callers out there, git tells me: > ... > But none of that seems like it cares about an extra few cycles, and why > complicate matters with another sync_core variant and all that. > ... > + * CPUID is the conventional way, but it's nasty: it doesn't > + * exist on some 486-like CPUs, and it usually exits to a > + * hypervisor. Hasn't support for those 486 cpu been dropped now? So the comment probably needs updating? David