Received-SPF: pass (google.com: domain of linux-kernel+bounces-155787-linux.lists.archive=gmail.com@vger.kernel.org designates 139.178.88.99 as permitted sender) client-ip=139.178.88.99;
Date: Tue, 23 Apr 2024 12:15:47 -0700
In-Reply-To: <20240423-0db9024011213dcffe815c5c@orel>
Precedence: bulk
Mime-Version: 1.0
References: <20240423073952.2001989-1-chentao@kylinos.cn> <878bf83c-cd5b-48d0-8b4e-77223f1806dc@web.de>
 <ZifMAWn32tZBQHs0@google.com> <20240423-0db9024011213dcffe815c5c@orel>
Message-ID: <ZigI48_cI7Twb9gD@google.com>
Subject: Re: [PATCH] KVM: selftests: Add 'malloc' failure check in test_vmx_nested_state
From: Sean Christopherson <seanjc@google.com>
To: Andrew Jones <ajones@ventanamicro.com>
Cc: Markus Elfring <Markus.Elfring@web.de>, Kunwu Chan <chentao@kylinos.cn>, 
	linux-kselftest@vger.kernel.org, kvm@vger.kernel.org, 
	kernel-janitors@vger.kernel.org, 
	Muhammad Usama Anjum <usama.anjum@collabora.com>, Paolo Bonzini <pbonzini@redhat.com>, 
	Shuah Khan <shuah@kernel.org>, LKML <linux-kernel@vger.kernel.org>, 
	Kunwu Chan <kunwu.chan@hotmail.com>, Anup Patel <anup@brainfault.org>, 
	Thomas Huth <thuth@redhat.com>, Oliver Upton <oliver.upton@linux.dev>
Content-Type: text/plain; charset="utf-8"
Content-Transfer-Encoding: quoted-printable

On Tue, Apr 23, 2024, Andrew Jones wrote:
> On Tue, Apr 23, 2024 at 07:56:01AM -0700, Sean Christopherson wrote:
> > +others
> >=20
> > On Tue, Apr 23, 2024, Markus Elfring wrote:
> > > =E2=80=A6
> > > > This patch will add the malloc failure checking
> > > =E2=80=A6
> > >=20
> > > * Please use a corresponding imperative wording for the change descri=
ption.
> > >=20
> > > * Would you like to add the tag =E2=80=9CFixes=E2=80=9D accordingly?
> >=20
> > Nah, don't bother with Fixes.  OOM will cause the test to fail regardle=
ss, the
> > fact that it gets an assert instead a NULL pointer deref is nice to hav=
e, but by
> > no means does it fix a bug.
> >=20
> > > > +++ 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 =3D sizeof(struct kvm_nested_state) + getpages=
ize();
> > > >  	struct kvm_nested_state *state =3D
> > > >  		(struct kvm_nested_state *)malloc(state_sz);
> > > > +	TEST_ASSERT(state, "-ENOMEM when allocating kvm state");
> > > =E2=80=A6
> > >=20
> > > Can =E2=80=9Cerrno=E2=80=9D be relevant for the error message constru=
ction?
> >=20
> > 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() fail=
ed for
> > blah blah blah". =20
> >=20
> > 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 collecti=
vely fail
> > to enforce checking on new code.
> >=20
> > E.g. something like (obviously won't compile, just for demonstration pu=
rposes)
> >=20
> > #define kvm_malloc(x)
> > ({
> > 	void *__ret;
> >=20
> > 	__ret  =3D malloc(x);
> > 	TEST_ASSERT(__ret, "Failed malloc(" #x ")\n");
> > 	__ret;
> > })
> >=20
> > #define kvm_calloc(x, y)
> > ({
> > 	void *__ret;
> >=20
> > 	__ret  =3D calloc(x, y);
> > 	TEST_ASSERT(__ret, "Failed calloc(" #x ", " #y ")\n");
> > 	__ret;
> > })
>=20
> 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 like test_* more than kvm_*, but I'm mildly concerned that readers will b=
e
confused by "test", e.g. initially thinking the "test" means it's just "tes=
ting"
if allocation is possible.

The obvious counter-argument is that people might also get tripped by kmall=
oc(),
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 conne=
cted
to KVM and/or selftests, but unique and short.

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