linux-kernel - Re: [PATCH v2 4/4] KVM: selftests: Add CPUID tests for Hyper-V features that need in-kernel APIC

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Message-ID: <Z4_Em95xkvagPOHN@google.com>
Date: Tue, 21 Jan 2025 08:00:27 -0800
From: Sean Christopherson <seanjc@...gle.com>
To: Vitaly Kuznetsov <vkuznets@...hat.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Dongjie Zou <zoudongjie@...wei.com>
Subject: Re: [PATCH v2 4/4] KVM: selftests: Add CPUID tests for Hyper-V
 features that need in-kernel APIC

On Mon, Jan 20, 2025, Vitaly Kuznetsov wrote:
> > diff --git a/tools/testing/selftests/kvm/x86_64/hyperv_cpuid.c b/tools/testing/selftests/kvm/x86_64/hyperv_cpuid.c
> > index 3188749ec6e1..8f26130dc30d 100644
> > --- a/tools/testing/selftests/kvm/x86_64/hyperv_cpuid.c
> > +++ b/tools/testing/selftests/kvm/x86_64/hyperv_cpuid.c
> > @@ -43,6 +43,7 @@ static bool smt_possible(void)
> >  
> >  static void test_hv_cpuid(struct kvm_vcpu *vcpu, bool evmcs_expected)
> >  {
> > +	const bool has_irqchip = !vcpu || vcpu->vm->has_irqchip;
> >  	const struct kvm_cpuid2 *hv_cpuid_entries;
> >  	int i;
> >  	int nent_expected = 10;
> > @@ -85,12 +86,19 @@ static void test_hv_cpuid(struct kvm_vcpu *vcpu, bool evmcs_expected)
> >  				    entry->eax, evmcs_expected
> >  				);
> >  			break;
> > +		case 0x40000003:
> > +			TEST_ASSERT(has_irqchip || !(entry->edx & BIT(19)),
> > +				    "Synthetic Timers should require in-kernel APIC");
> 
> Nitpick: BIT(19) of CPUID.0x40000003(EDX) advertises 'direct' mode
> for Synthetic timers and that's what we have paired with
> lapic_in_kernel() check. Thus, we may want to be a bit more specific and
> say
> 
> "Direct Synthetic timers should require in-kernel APIC"
> (personally, I'd prefer "Synthetic timers in 'direct' mode" name but
> that's not how TLFS calls them)

What about adding quotes to try and communicate that it's a property of Syntehtic
Timers?  E.g.

 "\"Direct\" Synthetic Timers should require in-kernel APIC");