From: Borislav Petkov <bp@alien8.de>
To: Sean Christopherson <seanjc@google.com>
Cc: Pavel Machek <pavel@denx.de>, Sasha Levin <sashal@kernel.org>,
linux-kernel@vger.kernel.org, stable@vger.kernel.org,
Max Grobecker <max@grobecker.info>,
Ingo Molnar <mingo@kernel.org>,
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 <pbonzini@redhat.com>
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)
Date: Sat, 26 Apr 2025 14:26:32 +0300 [thread overview]
Message-ID: <71D468BB-CE40-47DC-8E3D-74C336B15045@alien8.de> (raw)
In-Reply-To: <aAwj_Tkqj4GtywDe@google.com>
On April 26, 2025 3:08:29 AM GMT+03:00, Sean Christopherson <seanjc@google.com> wrote:
>The kernel already can enforce policy. Setting host breakpoints on guest code
>is done through a dedicated ioctl(), and access to said ioctl() can be restricted
>through various sandboxing methods, e.g. seccomp.
Ok, makes sense.
>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?
--
Sent from a small device: formatting sucks and brevity is inevitable.
next prev parent reply other threads:[~2025-04-26 11:27 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-03-31 14:37 [PATCH AUTOSEL 5.10 1/6] pm: cpupower: bench: Prevent NULL dereference on malloc failure Sasha Levin
2025-03-31 14:37 ` [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 Sasha Levin
2025-04-18 16:54 ` Pavel Machek
2025-04-18 17:19 ` Sean Christopherson
2025-04-18 17:36 ` Borislav Petkov
2025-04-18 18:31 ` Sean Christopherson
2025-04-18 19:12 ` Borislav Petkov
2025-04-22 17:22 ` Sean Christopherson
2025-04-22 17:33 ` 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) Borislav Petkov
2025-04-22 19:48 ` Sean Christopherson
2025-04-23 7:20 ` Borislav Petkov
2025-04-23 14:10 ` Sean Christopherson
2025-04-23 18:43 ` Borislav Petkov
2025-04-24 19:18 ` Sean Christopherson
2025-04-24 20:31 ` Borislav Petkov
2025-04-26 0:08 ` Sean Christopherson
2025-04-26 11:26 ` Borislav Petkov [this message]
2025-05-06 1:04 ` Sean Christopherson
2025-03-31 14:37 ` [PATCH AUTOSEL 5.10 3/6] perf: arm_pmu: Don't disable counter in armpmu_add() Sasha Levin
2025-03-31 14:37 ` [PATCH AUTOSEL 5.10 4/6] arm64: cputype: Add QCOM_CPU_PART_KRYO_3XX_GOLD Sasha Levin
2025-04-18 16:55 ` Pavel Machek
2025-04-18 19:27 ` Doug Anderson
2025-03-31 14:37 ` [PATCH AUTOSEL 5.10 5/6] xen/mcelog: Add __nonstring annotations for unterminated strings Sasha Levin
2025-03-31 14:37 ` [PATCH AUTOSEL 5.10 6/6] x86/mm/ident_map: Fix theoretical virtual address overflow to zero Sasha Levin
2025-04-18 16:52 ` [PATCH AUTOSEL 5.10 1/6] pm: cpupower: bench: Prevent NULL dereference on malloc failure Pavel Machek
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