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

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Message-ID: <ZoxAcAOVZ6I6Sidc@google.com>
Date: Mon, 8 Jul 2024 19:39:28 +0000
From: Sean Christopherson <seanjc@...gle.com>
To: Maxim Levitsky <mlevitsk@...hat.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>, Vitaly Kuznetsov <vkuznets@...hat.com>, 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 Thu, Jul 04, 2024, Maxim Levitsky wrote:
> 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.

Huh, I don't know.  I distinctly remember trying and failing to dedup this code,
but I don't think I ever tried actively toggling each bit.  I'll give that a shot.