linux-kernel - Re: [PATCH] selftests/kvm: Use vcpus count instead of hardcoded 0xff in test

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Message-ID: <CAHCkknocRNK=DWnmLVhrMDgBP6nW08HM=c6wGnHrjR1-Fbncnw@mail.gmail.com>
Date: Mon, 8 Sep 2025 22:23:59 +0200
From: sukrut heroorkar <hsukrut3@...il.com>
To: Sean Christopherson <seanjc@...gle.com>
Cc: skhan@...uxfoundation.org, david.hunter.linux@...il.com, 
	Paolo Bonzini <pbonzini@...hat.com>, Shuah Khan <shuah@...nel.org>, 
	"open list:KERNEL VIRTUAL MACHINE FOR X86 (KVM/x86)" <kvm@...r.kernel.org>, 
	"open list:KERNEL SELFTEST FRAMEWORK" <linux-kselftest@...r.kernel.org>, open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] selftests/kvm: Use vcpus count instead of hardcoded 0xff
 in test_icr

Hi Sean,

On Mon, Sep 8, 2025 at 4:30 PM Sean Christopherson <seanjc@...gle.com> wrote:
>
> On Sat, Sep 06, 2025, Sukrut Heroorkar wrote:
> > Replace the hardcoded 0xff in test_icr() with the actual number of vcpus
> > created for the vm. This address the existing TODO and keeps the test
> > correct if it is ever run with multiple vcpus.
>
> The TODO is stale, it was resolved by commit 376bc1b458c9 ("KVM: selftests: Don't
> assume vcpu->id is '0' in xAPIC state test"), I/we just forgot to delete the
> comment.
>
> > Signed-off-by: Sukrut Heroorkar <hsukrut3@...il.com>
> > ---
> >  tools/testing/selftests/kvm/x86/xapic_state_test.c | 13 ++++++++++++-
> >  1 file changed, 12 insertions(+), 1 deletion(-)
> >
> > diff --git a/tools/testing/selftests/kvm/x86/xapic_state_test.c b/tools/testing/selftests/kvm/x86/xapic_state_test.c
> > index fdebff1165c7..4af36682503e 100644
> > --- a/tools/testing/selftests/kvm/x86/xapic_state_test.c
> > +++ b/tools/testing/selftests/kvm/x86/xapic_state_test.c
> > @@ -56,6 +56,17 @@ static void x2apic_guest_code(void)
> >       } while (1);
> >  }
> >
> > +static unsigned int vm_nr_vcpus(struct kvm_vm *vm)
> > +{
> > +     struct kvm_vcpu *vcpu;
> > +     unsigned int count = 0;
> > +
> > +     list_for_each_entry(vcpu, &vm->vcpus, list)
> > +             count++;
> > +
> > +     return count;
> > +}
> > +
> >  static void ____test_icr(struct xapic_vcpu *x, uint64_t val)
> >  {
> >       struct kvm_vcpu *vcpu = x->vcpu;
> > @@ -124,7 +135,7 @@ static void test_icr(struct xapic_vcpu *x)
> >        * vCPUs, not vcpu.id + 1.  Arbitrarily use vector 0xff.
> >        */
> >       icr = APIC_INT_ASSERT | 0xff;
> > -     for (i = 0; i < 0xff; i++) {
> > +     for (i = 0; i < vm_nr_vcpus(vcpu->vm); i++) {
>
> This is wrong/undesirable.  The original code was:
>
>         for (i = vcpu->id + 1; i < 0xff; i++) {
>                 for (j = 0; j < 8; j++)
>                         __test_icr(vm, vcpu, i << (32 + 24) | APIC_INT_ASSERT | (j << 8));
>         }
>
> I.e. the _lower_ bound was nr_vcpus+1.  Regardless, as fixed by the aformentioned
> commit, using the number of vCPUs in any capacity is simply wrong.  The stale
> comment just needs to be deleted.:

Thanks for the clarification. I will send a patch removing the stale
TODO comment.
>
> >               if (i == vcpu->id)
> >                       continue;
> >               for (j = 0; j < 8; j++)
> > --
> > 2.43.0
> >