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

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Date: Wed, 24 Apr 2024 10:59:31 +0800
From: Kunwu Chan <kunwu.chan@...mail.com>
To: Sean Christopherson <seanjc@...gle.com>,
 Andrew Jones <ajones@...tanamicro.com>, chentao@...inos.cn
Cc: Markus Elfring <Markus.Elfring@....de>, 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

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.