Re: [PATCH] KVM: selftests: Add 'malloc' failure check in test_vmx_nested_state

[Andrew Jones]

On Tue, Apr 23, 2024 at 07:56:01AM -0700, Sean Christopherson wrote:
> +others
> 
> On Tue, Apr 23, 2024, Markus Elfring wrote:
> > …
> > > This patch will add the malloc failure checking
> > …
> > 
> > * Please use a corresponding imperative wording for the change description.
> > 
> > * Would you like to add the tag “Fixes” accordingly?
> 
> Nah, don't bother with Fixes.  OOM will cause the test to fail regardless, the
> fact that it gets an assert instead a NULL pointer deref is nice to have, but by
> no means does it fix a bug.
> 
> > > +++ b/tools/testing/selftests/kvm/x86_64/vmx_set_nested_state_test.c
> > > @@ -91,6 +91,7 @@ void test_vmx_nested_state(struct kvm_vcpu *vcpu)
> > >  	const int state_sz = sizeof(struct kvm_nested_state) + getpagesize();
> > >  	struct kvm_nested_state *state =
> > >  		(struct kvm_nested_state *)malloc(state_sz);
> > > +	TEST_ASSERT(state, "-ENOMEM when allocating kvm state");
> > …
> > 
> > Can “errno” be relevant for the error message construction?
> 
> Probably not, but there's also no reason to assume ENOMEM.  TEST_ASSERT() spits
> out the actual errno, and we can just say something like "malloc() failed for
> blah blah blah".  
> 
> But rather than keeping playing whack-a-mole, what if we add macros to perform
> allocations and assert on the result?  I have zero interest in chasing down all
> of the "unsafe" allocations, and odds are very good that we'll collectively fail
> to enforce checking on new code.
> 
> E.g. something like (obviously won't compile, just for demonstration purposes)
> 
> #define kvm_malloc(x)
> ({
> 	void *__ret;
> 
> 	__ret  = malloc(x);
> 	TEST_ASSERT(__ret, "Failed malloc(" #x ")\n");
> 	__ret;
> })
> 
> #define kvm_calloc(x, y)
> ({
> 	void *__ret;
> 
> 	__ret  = calloc(x, y);
> 	TEST_ASSERT(__ret, "Failed calloc(" #x ", " #y ")\n");
> 	__ret;
> })

Sounds good to me, but I'd call them test_malloc, test_calloc, etc. and
put them in include/test_util.h

Thanks,
drew