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Sat, 26 Apr 2025 11:26:37 +0000 (UTC) Date: Sat, 26 Apr 2025 14:26:32 +0300 From: Borislav Petkov To: Sean Christopherson 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 Subject: =?US-ASCII?Q?Re=3A_CONFIG=5FX86=5FHYPERVISOR_=28was=3A_Re=3A_=5BPATC?= =?US-ASCII?Q?H_AUTOSEL_5=2E10_2/6=5D_x86/cpu=3A_Don=27t_clear_?= =?US-ASCII?Q?X86=5FFEATURE=5FLAHF=5FLM_flag_in_init=5Famd=5Fk8=28=29?= =?US-ASCII?Q?_on_AMD_when_running_in_a_virtual_machine=29?= User-Agent: K-9 Mail for Android In-Reply-To: References: <20250418191224.GFaAKkGBnb01tGUVhW@fat_crate.local> <20250422173355.GDaAfTA8GqnGBfDk7G@renoirsky.local> <20250423072017.GAaAiUsYzDOdt7cmp2@renoirsky.local> <20250423184326.GCaAk0zinljkNHa_M7@renoirsky.local> <20250424203110.GCaAqfjnr-fogRgnt7@renoirsky.local> Message-ID: <71D468BB-CE40-47DC-8E3D-74C336B15045@alien8.de> 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=utf-8 Content-Transfer-Encoding: quoted-printable On April 26, 2025 3:08:29 AM GMT+03:00, Sean Christopherson wrote: >The kernel already can enforce policy=2E Setting host breakpoints on gue= st code >is done through a dedicated ioctl(), and access to said ioctl() can be re= stricted >through various sandboxing methods, e=2Eg=2E seccomp=2E Ok, makes sense=2E >No, that would defeat the purpose of the check=2E The X86_FEATURE_HYPERV= ISOR has >nothing to do with correctness, it's all about performance=2E Critically= , it's a >static check that gets patched at runtime=2E It's a micro-optimization f= or bare >metal to avoid a single cache miss (the __this_cpu_read(cpu_dr7))=2E Rou= ting >through cc_platform_has() would be far, far heavier than calling hw_break= point_active()=2E Huh, we care so much about speed here? --=20 Sent from a small device: formatting sucks and brevity is inevitable=2E