linux-kernel - Re: [PATCH v2 05/49] KVM: selftests: Assert that the @cpuid passed to get_cpuid

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Message-ID: <Zow_BmpOGwQJ9Yoi@google.com>
Date: Mon, 8 Jul 2024 19:33:26 +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 05/49] KVM: selftests: Assert that the @cpuid passed to
 get_cpuid_entry() is non-NULL

On Thu, Jul 04, 2024, Maxim Levitsky wrote:
> On Fri, 2024-05-17 at 10:38 -0700, Sean Christopherson wrote:
> > Add a sanity check in get_cpuid_entry() to provide a friendlier error than
> > a segfault when a test developer tries to use a vCPU CPUID helper on a
> > barebones vCPU.
> > 
> > Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> > ---
> >  tools/testing/selftests/kvm/lib/x86_64/processor.c | 2 ++
> >  1 file changed, 2 insertions(+)
> > 
> > diff --git a/tools/testing/selftests/kvm/lib/x86_64/processor.c b/tools/testing/selftests/kvm/lib/x86_64/processor.c
> > index c664e446136b..f0f3434d767e 100644
> > --- a/tools/testing/selftests/kvm/lib/x86_64/processor.c
> > +++ b/tools/testing/selftests/kvm/lib/x86_64/processor.c
> > @@ -1141,6 +1141,8 @@ const struct kvm_cpuid_entry2 *get_cpuid_entry(const struct kvm_cpuid2 *cpuid,
> >  {
> >  	int i;
> >  
> > +	TEST_ASSERT(cpuid, "Must do vcpu_init_cpuid() first (or equivalent)");
> > +
> >  	for (i = 0; i < cpuid->nent; i++) {
> >  		if (cpuid->entries[i].function == function &&
> >  		    cpuid->entries[i].index == index)
> 
> Hi,
> 
> Maybe it is better to do this assert in __vcpu_get_cpuid_entry() because the
> assert might confuse the reader, since it just tests for NULL but when it
> fails, it complains that you need to call some function.

IIRC, I originally added the assert in __vcpu_get_cpuid_entry(), but I didn't
like leaving get_cpuid_entry() unprotected.  What if I add an assert in both?
E.g. have __vcpu_get_cpuid_entry() assert with the (hopefully) hepful message,
and have get_cpuid_entry() do a simple TEST_ASSERT_NE()?