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: <87wmeo6sgt.fsf@redhat.com>
Date: Tue, 21 Jan 2025 17:29:22 +0100
From: Vitaly Kuznetsov <vkuznets@...hat.com>
To: Sean Christopherson <seanjc@...gle.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

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

> 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");

Sounds good to me)

-- 
Vitaly