linux-kernel - Re: [PATCH v2 07/49] KVM: selftests: Verify KVM stuffs runtime CPUID OS bits on CR4 writes

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Date: Thu, 04 Jul 2024 21:02:27 -0400
From: Maxim Levitsky <mlevitsk@...hat.com>
To: Sean Christopherson <seanjc@...gle.com>, Paolo Bonzini
 <pbonzini@...hat.com>,  Vitaly Kuznetsov <vkuznets@...hat.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org, Hou Wenlong
 <houwenlong.hwl@...group.com>, Kechen Lu <kechenl@...dia.com>, Oliver Upton
 <oliver.upton@...ux.dev>, Binbin Wu <binbin.wu@...ux.intel.com>, Yang
 Weijiang <weijiang.yang@...el.com>, Robert Hoo <robert.hoo.linux@...il.com>
Subject: Re: [PATCH v2 07/49] KVM: selftests: Verify KVM stuffs runtime
 CPUID OS bits on CR4 writes

On Fri, 2024-05-17 at 10:38 -0700, Sean Christopherson wrote:
> Extend x86's set sregs test to verify that KVM sets/clears OSXSAVE and
> OSKPKE according to CR4.XSAVE and CR4.PKE respectively.  For performance
> reasons, KVM is responsible for emulating the architectural behavior of
> the OS CPUID bits tracking CR4.
> 
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
>  tools/testing/selftests/kvm/x86_64/set_sregs_test.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/tools/testing/selftests/kvm/x86_64/set_sregs_test.c b/tools/testing/selftests/kvm/x86_64/set_sregs_test.c
> index 96fd690d479a..f4095a3d1278 100644
> --- a/tools/testing/selftests/kvm/x86_64/set_sregs_test.c
> +++ b/tools/testing/selftests/kvm/x86_64/set_sregs_test.c
> @@ -85,6 +85,16 @@ static void test_cr_bits(struct kvm_vcpu *vcpu, uint64_t cr4)
>  	rc = _vcpu_sregs_set(vcpu, &sregs);
>  	TEST_ASSERT(!rc, "Failed to set supported CR4 bits (0x%lx)", cr4);
>  
> +	TEST_ASSERT(!!(sregs.cr4 & X86_CR4_OSXSAVE) ==
> +		    (vcpu->cpuid && vcpu_cpuid_has(vcpu, X86_FEATURE_OSXSAVE)),
> +		    "KVM didn't %s OSXSAVE in CPUID as expected",
> +		    (sregs.cr4 & X86_CR4_OSXSAVE) ? "set" : "clear");
> +
> +	TEST_ASSERT(!!(sregs.cr4 & X86_CR4_PKE) ==
> +		    (vcpu->cpuid && vcpu_cpuid_has(vcpu, X86_FEATURE_OSPKE)),
> +		    "KVM didn't %s OSPKE in CPUID as expected",
> +		    (sregs.cr4 & X86_CR4_PKE) ? "set" : "clear");
> +

Hi,

Just for fun, why not to have a test function that toggles a CR4 bit and then
checks the corresponding CPUID bit toggles as well? This is both better
coverage wise and will remove the above code duplication.

Best regards,
	Maxim Levitsky


>  	vcpu_sregs_get(vcpu, &sregs);
>  	TEST_ASSERT(sregs.cr4 == cr4, "sregs.CR4 (0x%llx) != CR4 (0x%lx)",
>  		    sregs.cr4, cr4);