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

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Message-ID: <aL7ogKtOUi2py1jx@google.com>
Date: Mon, 8 Sep 2025 07:30:24 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Sukrut Heroorkar <hsukrut3@...il.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

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.:

>  		if (i == vcpu->id)
>  			continue;
>  		for (j = 0; j < 8; j++)
> -- 
> 2.43.0
>