linux-kernel - Re: [RFC PATCH v5 075/104] KVM: x86: Check for pending APICv interrupt in kvm_vcpu_has

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Message-ID: <1bff7526-c532-3ca8-7d7a-c7face576a37@redhat.com>
Date:   Fri, 15 Apr 2022 16:20:09 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>, isaku.yamahata@...el.com
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        isaku.yamahata@...il.com, Jim Mattson <jmattson@...gle.com>,
        erdemaktas@...gle.com, Connor Kuehl <ckuehl@...hat.com>
Subject: Re: [RFC PATCH v5 075/104] KVM: x86: Check for pending APICv
 interrupt in kvm_vcpu_has_events()

On 4/8/22 18:24, Sean Christopherson wrote:
>> Return true for kvm_vcpu_has_events() if the vCPU has a pending APICv
>> interrupt to support TDX's usage of APICv.  Unlike VMX, TDX doesn't have
>> access to vmcs.GUEST_INTR_STATUS and so can't emulate posted interrupts,
> Based on the discussion in the HLT patch, this is no longer true.
> 

It's still true, it only has access to RVI > PPR (which is enough to check
if the vCPU is runnable).

> Rather than hook this path, I would rather we tag kvm_apic has having some of its
> state protected.  Then kvm_cpu_has_interrupt() can invoke the alternative,
> protected-apic-only hook when appropriate, and kvm_apic_has_interrupt() can bail
> immediately instead of doing useless processing of stale vAPIC state.

Agreed, this is similar to my suggestion on the HLT patch:

https://lkml.kernel.org/r/a7d28775-2dbe-7d97-7053-e182bd5be51c@redhat.com

Paolo