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b=mXkGnTpwyh8bt6K3FX95aOFlhzYfrE8zznPIHQcB6ZSkJXMCIuRdC3dUNuPEfTu9JmlS5xe4DgWXTavOWIVRGLAlsx/Qy1+4VFp+sn75RW7Lbl3FQmo4tiT8Uukz4Nef32ncTpuUE8jLxQDlDXQog2KDWAMfSz6oQDeHG+/PhG0= Authentication-Results: dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=amd.com; Received: from BL3PR12MB9049.namprd12.prod.outlook.com (2603:10b6:208:3b8::21) by CHXPR12MB999222.namprd12.prod.outlook.com (2603:10b6:610:2f9::16) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.21.25.21; Thu, 28 May 2026 19:37:21 +0000 Received: from BL3PR12MB9049.namprd12.prod.outlook.com ([fe80::ae6a:9bdd:af5b:e9ad]) by BL3PR12MB9049.namprd12.prod.outlook.com ([fe80::ae6a:9bdd:af5b:e9ad%6]) with mapi id 15.21.0071.011; Thu, 28 May 2026 19:37:20 +0000 Message-ID: <2d164e19-5cc6-47ca-9150-f4d432dd10c4@amd.com> Date: Thu, 28 May 2026 14:37:16 -0500 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v5 2/7] x86/msr: add wrmsrq_on_cpus helper To: Borislav Petkov , Dave Hansen Cc: tglx@kernel.org, mingo@redhat.com, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, seanjc@google.com, peterz@infradead.org, thomas.lendacky@amd.com, herbert@gondor.apana.org.au, davem@davemloft.net, ardb@kernel.org, pbonzini@redhat.com, aik@amd.com, Michael.Roth@amd.com, KPrateek.Nayak@amd.com, Tycho.Andersen@amd.com, Nathan.Fontenot@amd.com, ackerleytng@google.com, jackyli@google.com, pgonda@google.com, rientjes@google.com, jacobhxu@google.com, xin@zytor.com, pawan.kumar.gupta@linux.intel.com, babu.moger@amd.com, dyoung@redhat.com, nikunj@amd.com, john.allen@amd.com, darwi@linutronix.de, linux-kernel@vger.kernel.org, linux-crypto@vger.kernel.org, kvm@vger.kernel.org, linux-coco@lists.linux.dev References: <20260527210603.GCahdcu8zvVjfKfGEL@fat_crate.local> <20260528004332.GDahePtGqVp2boiEJL@fat_crate.local> Content-Language: en-US From: "Kalra, Ashish" In-Reply-To: <20260528004332.GDahePtGqVp2boiEJL@fat_crate.local> Content-Type: text/plain; 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I think it only has a single user. It's >> also not very flexible because it needs a 'struct msr __percpu *msrs' >> argument where each MSR has a value in memory. > > Right, we did that a looong time ago. > > The only reason I'd have for per-CPU MSR structs is reading different MSR > values on different cores, modifying only the bits you need and then *keeping* > the remaining values as they were. And that interface allows you to do that > while this new thing won't. > > And I'm going to venture a guess here that adding a simpler interface which > simply forces a new value ontop of a whole MSR could cause a lot of subtle > bugs when people don't pay attention to keep the old values. > >> The use case for RMPOPT is that all CPUs get the same value. It'd be a >> little awkward to go create a percpu data structure to duplcate the same >> value to call wrmsr_on_cpus(). The RMPOPT case is also arguably >> performance sensitive since it's done during boot. It should do the IPIs >> in parallel. > > Oh sure, my meaning was to create something that serves both purposes. > >> toggle_ecc_err_reporting(), on the other hand, is done at module init >> time. It's not really performance sensitive. It's probably pretty easy >> to zap wrmsr_on_cpus() and just have toggle_ecc_err_reporting() do >> something slightly less efficient. > > Sure. That's fine. > >> Yeah, the >> >> wrmsr_on_cpus() >> wrmsrq_on_cpus() >> >> naming pain is real. There's little chance of bugs coming from it >> because the function signatures are *SO* different. But, it certainly >> could confuse humans for a minute. > > Yap. > >> But the real solution to this is axing wrmsr_on_cpus(). > > Yap, for example. Basically reingeneering the whole > write-MSRs-on-multiple-CPUs functionality is what I meant. > >> Which I think we could do after killing its one user which the attached >> (completely untested) patch does. The only downside of the patch is that it >> does RDMSR via IPIs one CPU at a time. But, looking at the code, I'm not >> sure anyone would care. If anyone did, I _think_ all those MSRs have the >> same value and the code could be simplified further. But that would take >> more than 3 minutes. >> >> It's also possible that my grepping was bad or I'm completely >> misunderstanding amd64_edac.c. Cluebat welcome if I'm being dense. > > Looks ok to me, we can surely do that. I even hw to test it. I think... > >> BTW, I also don't feel the need to make Ashish go do any of this edac >> cleanup. I think it can just be done in parallel. But I wouldn't stop >> him if he volunteered. > > Why not? > > It has always been the case: cleanups and bug fixes first, new features ontop. > > So yeah, modulo figuring out how to redefine the *msr_on_cpus() interface, > I think this all makes sense. snp_setup_rmpopt() runs once during init and rmpopt_cleanup() runs once during shutdown. The batch IPI optimization is irrelevant here. This RMPOPT_BASE MSR setup/programming is not in a performance critical path. A simple loop would be perfectly fine and avoids the need for the wrmsrq_on_cpus() helper entirely: for_each_cpu(cpu, &rmpopt_cpumask) wrmsrq_on_cpu(cpu, MSR_AMD64_RMPOPT_BASE, rmpopt_base); Calling wrmsrq_on_cpus() here for programming RMPOPT_BASE MSR: - wrmsrq_on_cpus(&rmpopt_cpumask, MSR_AMD64_RMPOPT_BASE, rmpopt_base); + for_each_cpu(cpu, &rmpopt_cpumask) + wrmsrq_on_cpu(cpu, MSR_AMD64_RMPOPT_BASE, rmpopt_base); So i will drop this helper patch. Thanks, Ashish > > Thx. >