linux-kernel - Re: [PATCH 0/3] KVM: x86: Fix KVM_FEATURE_PV

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Message-ID: <87plw5knp5.fsf@redhat.com>
Date: Fri, 08 Mar 2024 11:44:22 +0100
From: Vitaly Kuznetsov <vkuznets@...hat.com>
To: Sean Christopherson <seanjc@...gle.com>
Cc: Li RongQing <lirongqing@...du.com>, linux-kernel@...r.kernel.org,
 kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [PATCH 0/3] KVM: x86: Fix KVM_FEATURE_PV_UNHALT update logic

Sean Christopherson <seanjc@...gle.com> writes:

> On Wed, 28 Feb 2024 11:18:34 +0100, Vitaly Kuznetsov wrote:
>> Guest hangs in specific configurations (KVM_X86_DISABLE_EXITS_HLT) are
>> reported and the issue was bisected to commit ee3a5f9e3d9b ("KVM: x86: Do
>> runtime CPUID update before updating vcpu->arch.cpuid_entries") which, of
>> course, carries "No functional change intended" blurb. Turns out, moving
>> __kvm_update_cpuid_runtime() earlier in kvm_set_cpuid() to tweak the
>> incoming CPUID data before checking it wasn't innocent as
>> KVM_FEATURE_PV_UNHALT reset logic relies on cached KVM CPUID base which
>> gets updated later.
>> 
>> [...]
>
> Applied to kvm-x86 hyperv.  I won't send a pull request for this until next week,
> but I do plan on landing it in 6.9.  Holler if the selftests tweaks look wrong
> (or you just don't like them).

Looks great, thanks :-)

I was also considering introducing 'vcpu_cpuid_has()' first but then I
succumbed to my laziness and decided to postpone it until we have a
*second* user in the tree).

-- 
Vitaly