From: Naveen N Rao <naveen@kernel.org>
To: Sean Christopherson <seanjc@google.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
Thomas Gleixner <tglx@kernel.org>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
Kai Huang <kai.huang@intel.com>, Yosry Ahmed <yosry@kernel.org>
Subject: Re: [PATCH] x86/apic: KVM: Use cpu_physical_id() to get APIC ID of running vCPU for AVIC
Date: Tue, 16 Jun 2026 13:27:51 +0530 [thread overview]
Message-ID: <ajDsUg236ilh40YZ@blrnaveerao1> (raw)
In-Reply-To: <20260612185459.591892-1-seanjc@google.com>
On Fri, Jun 12, 2026 at 11:54:59AM -0700, Sean Christopherson wrote:
> Use cpu_physical_id() instead of default_cpu_present_to_apicid() when
> getting the APIC ID of the pCPU on which a vCPU is running/loaded, as the
> kernel has gone way off the rails if a vCPU is loaded on a pCPU that has
> been physically removed from the system.
Or, has been unloaded from a pCPU that is then soft-offlined and
physically hot unplugged before that vCPU ever got a chance to run
again!
> Even if the impossible were to
> happen, the absolutely worst case scenario is that hardware will ring the
> AIVC doorbell on the wrong pCPU, i.e. a severely broken system will
> experience mild performance issues.
Indeed, sending a doorbell to BAD_APICID doesn't seem to do anything
bad, so I think we are ok with this.
>
> Kill off KVM's superfluous kvm_cpu_get_apicid() wrapper along with the
> for-KVM export of default_cpu_present_to_apicid(), as they existed purely
> for the wonky AVIC usage.
>
> Cc: Kai Huang <kai.huang@intel.com>
> Cc: Yosry Ahmed <yosry@kernel.org>
> Signed-off-by: Sean Christopherson <seanjc@google.com>
Acked-by: Naveen N Rao (AMD) <naveen@kernel.org>
- Naveen
prev parent reply other threads:[~2026-06-16 7:59 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-06-12 18:54 [PATCH] x86/apic: KVM: Use cpu_physical_id() to get APIC ID of running vCPU for AVIC Sean Christopherson
2026-06-12 21:26 ` Yosry Ahmed
2026-06-15 2:00 ` Huang, Kai
2026-06-16 7:57 ` Naveen N Rao [this message]
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