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

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Message-ID: <3aeeed2f4ccca6ddd404553984f22bf1b72e45cf.camel@redhat.com>
Date: Wed, 24 Jul 2024 13:28:40 -0400
From: Maxim Levitsky <mlevitsk@...hat.com>
To: Sean Christopherson <seanjc@...gle.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 Mon, 2024-07-08 at 19:33 +0000, Sean Christopherson wrote:
> 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()?
> 

This looks like a great idea.

Best regards,
	Maxim Levitsky