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AJvYcCW4Z177xXUI3wjhfpRa568WrgZYmWx3K3EF/+syaUI5RlZJW5+F+d0NHVyTVm8mied+lRIQ0Ec=@vger.kernel.org X-Gm-Message-State: AOJu0YwUIkzEmCoyJHVim0s7VlQXUxfh/fmMLTaptviLVZq7fbWjbGRI dUKs7K6eNUxNtdH6WDX6upxapt4Mw3uM8AGBYuqSQA+w0PMdndMbQ+6IpOE37YNfsBqe/hSSwnt 11A== X-Google-Smtp-Source: AGHT+IGdlsB+EHSVfbtv8XHlKK/WjJXJWIgHA3FCb9kGzawtjlIfFplRDWV+n/TPPTG4wzGKzuChBtuKRNY= X-Received: from pjbkl6.prod.google.com ([2002:a17:90b:4986:b0:2ef:8055:93d9]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a17:90b:578f:b0:2ee:f076:20f1 with SMTP id 98e67ed59e1d1-30a6174fda0mr16698675a91.0.1746493472687; Mon, 05 May 2025 18:04:32 -0700 (PDT) Date: Mon, 5 May 2025 18:04:31 -0700 In-Reply-To: <71D468BB-CE40-47DC-8E3D-74C336B15045@alien8.de> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20250422173355.GDaAfTA8GqnGBfDk7G@renoirsky.local> <20250423072017.GAaAiUsYzDOdt7cmp2@renoirsky.local> <20250423184326.GCaAk0zinljkNHa_M7@renoirsky.local> <20250424203110.GCaAqfjnr-fogRgnt7@renoirsky.local> <71D468BB-CE40-47DC-8E3D-74C336B15045@alien8.de> Message-ID: Subject: Re: CONFIG_X86_HYPERVISOR (was: Re: [PATCH AUTOSEL 5.10 2/6] x86/cpu: Don't clear X86_FEATURE_LAHF_LM flag in init_amd_k8() on AMD when running in a virtual machine) From: Sean Christopherson To: Borislav Petkov Cc: Pavel Machek , Sasha Levin , linux-kernel@vger.kernel.org, stable@vger.kernel.org, Max Grobecker , Ingo Molnar , tglx@linutronix.de, mingo@redhat.com, dave.hansen@linux.intel.com, x86@kernel.org, thomas.lendacky@amd.com, perry.yuan@amd.com, mario.limonciello@amd.com, riel@surriel.com, mjguzik@gmail.com, darwi@linutronix.de, Paolo Bonzini Content-Type: text/plain; charset="us-ascii" On Sat, Apr 26, 2025, Borislav Petkov wrote: > On April 26, 2025 3:08:29 AM GMT+03:00, Sean Christopherson wrote: > >No, that would defeat the purpose of the check. The X86_FEATURE_HYPERVISOR has > >nothing to do with correctness, it's all about performance. Critically, it's a > >static check that gets patched at runtime. It's a micro-optimization for bare > >metal to avoid a single cache miss (the __this_cpu_read(cpu_dr7)). Routing > >through cc_platform_has() would be far, far heavier than calling hw_breakpoint_active(). > > Huh, we care so much about speed here? That's a PeterZ question :-)