linux-kernel - Re: [PATCH] KVM: selftests: Add 'malloc' failure check in test_vmx_nested

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Message-ID: <20240423-0db9024011213dcffe815c5c@orel>
Date: Tue, 23 Apr 2024 17:14:52 +0200
From: Andrew Jones <ajones@...tanamicro.com>
To: Sean Christopherson <seanjc@...gle.com>
Cc: Markus Elfring <Markus.Elfring@....de>, 
	Kunwu Chan <chentao@...inos.cn>, linux-kselftest@...r.kernel.org, kvm@...r.kernel.org, 
	kernel-janitors@...r.kernel.org, Muhammad Usama Anjum <usama.anjum@...labora.com>, 
	Paolo Bonzini <pbonzini@...hat.com>, Shuah Khan <shuah@...nel.org>, 
	LKML <linux-kernel@...r.kernel.org>, Kunwu Chan <kunwu.chan@...mail.com>, 
	Anup Patel <anup@...infault.org>, Thomas Huth <thuth@...hat.com>, 
	Oliver Upton <oliver.upton@...ux.dev>
Subject: Re: [PATCH] KVM: selftests: Add 'malloc' failure check in
 test_vmx_nested_state

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