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

[Kunwu Chan]

Thanks all for the reply.

On 2024/4/24 03:15, Sean Christopherson wrote:
> On Tue, Apr 23, 2024, Andrew Jones wrote:
> > 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
> Possibly terrible idea: what if we used kmalloc() and kcalloc()?  K is for KVM :-)
I'am agree with that we should keep opening state for other memory 
allocate calls as well.
> I like test_* more than kvm_*, but I'm mildly concerned that readers will be
> confused by "test", e.g. initially thinking the "test" means it's just "testing"
> if allocation is possible.
>
> The obvious counter-argument is that people might also get tripped by kmalloc(),
> e.g. thinking that selftests is somehow doing a kernel allocation.
>
> I almost wonder if we should just pick a prefix that's less obviously connected
> to KVM and/or selftests, but unique and short.
It's a good idea.  The marco should be more versatile, cause we had many 
different way in selftests to check the null pointer or fail state, such 
as '
ksft_exit_fail_*' 'ASSERT_*' 'CHECK*' or just use if statement. 
Different part different developer has different usage habits.
We should think these status quo before doing sth.
> Hmm, tmalloc(), i.e t[est]malloc()?  tcalloc() gets a bit close to Google's
> TCMalloc[*], but I suspect that any confusion would be entirely limited to
> Googlers, and I'll volunteer us to suck it up and deal with it :-)
>
> [*] https://github.com/google/tcmalloc

And another question is if we add a new macro, whether these old usage 
should be changed as well.

Thanks for your reply.

Looking forward to your reply.