[PATCH] KVM: selftests: Relax assertion on HLT exits if CPU supports Idle HLT

[PATCH] KVM: selftests: Relax assertion on HLT exits if CPU supports Idle HLT

[Sean Christopherson]

If the CPU supports Idle HLT, which elides HLT VM-Exits if the vCPU has an
unmasked pending IRQ or NMI, relax the xAPIC IPI test's assertion on the
number of HLT exits to only require that the number of exits is less than
or equal to the number of HLT instructions that were executed.  I.e. don't
fail the test if Idle HLT does what it's supposed to do.

Note, unfortunately there's no way to determine if *KVM* supports Idle HLT,
as this_cpu_has() checks raw CPU support, and kvm_cpu_has() checks what can
be exposed to L1, i.e. the latter would check if KVM supports nested Idle
HLT.  But, since the assert is purely bonus coverage, checking for CPU
support is good enough.

Cc: Manali Shukla <Manali.Shukla@amd.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 tools/testing/selftests/kvm/include/x86/processor.h |  1 +
 tools/testing/selftests/kvm/x86/xapic_ipi_test.c    | 13 ++++++++++++-
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/kvm/include/x86/processor.h b/tools/testing/selftests/kvm/include/x86/processor.h
index 61578f038aff..32ab6ca7ec32 100644
--- a/tools/testing/selftests/kvm/include/x86/processor.h
+++ b/tools/testing/selftests/kvm/include/x86/processor.h
@@ -200,6 +200,7 @@ struct kvm_x86_cpu_feature {
 #define X86_FEATURE_PAUSEFILTER         KVM_X86_CPU_FEATURE(0x8000000A, 0, EDX, 10)
 #define X86_FEATURE_PFTHRESHOLD         KVM_X86_CPU_FEATURE(0x8000000A, 0, EDX, 12)
 #define	X86_FEATURE_VGIF		KVM_X86_CPU_FEATURE(0x8000000A, 0, EDX, 16)
+#define X86_FEATURE_IDLE_HLT		KVM_X86_CPU_FEATURE(0x8000000A, 0, EDX, 30)
 #define X86_FEATURE_SEV			KVM_X86_CPU_FEATURE(0x8000001F, 0, EAX, 1)
 #define X86_FEATURE_SEV_ES		KVM_X86_CPU_FEATURE(0x8000001F, 0, EAX, 3)
 #define	X86_FEATURE_PERFMON_V2		KVM_X86_CPU_FEATURE(0x80000022, 0, EAX, 0)
diff --git a/tools/testing/selftests/kvm/x86/xapic_ipi_test.c b/tools/testing/selftests/kvm/x86/xapic_ipi_test.c
index b255c7fbe519..35cb9de54a82 100644
--- a/tools/testing/selftests/kvm/x86/xapic_ipi_test.c
+++ b/tools/testing/selftests/kvm/x86/xapic_ipi_test.c
@@ -466,7 +466,18 @@ int main(int argc, char *argv[])
 	cancel_join_vcpu_thread(threads[0], params[0].vcpu);
 	cancel_join_vcpu_thread(threads[1], params[1].vcpu);
 
-	TEST_ASSERT_EQ(data->hlt_count, vcpu_get_stat(params[0].vcpu, halt_exits));
+	/*
+	 * If the host support Idle HLT, i.e. KVM *might* be using Idle HLT,
+	 * then the number of HLT exits may be less than the number of HLTs
+	 * that were executed, as Idle HLT elides the exit if the vCPU has an
+	 * unmasked, pending IRQ (or NMI).
+	 */
+	if (this_cpu_has(X86_FEATURE_IDLE_HLT))
+		TEST_ASSERT(data->hlt_count >= vcpu_get_stat(params[0].vcpu, halt_exits),
+			    "HLT insns = %lu, HLT exits = %lu",
+			    data->hlt_count, vcpu_get_stat(params[0].vcpu, halt_exits));
+	else
+		TEST_ASSERT_EQ(data->hlt_count, vcpu_get_stat(params[0].vcpu, halt_exits));
 
 	fprintf(stderr,
 		"Test successful after running for %d seconds.\n"

base-commit: fed48e2967f402f561d80075a20c5c9e16866e53
-- 
2.48.1.711.g2feabab25a-goog

Re: [PATCH] KVM: selftests: Relax assertion on HLT exits if CPU supports Idle HLT

[Manali Shukla]

On 2/27/2025 4:48 AM, Sean Christopherson wrote:
> If the CPU supports Idle HLT, which elides HLT VM-Exits if the vCPU has an
> unmasked pending IRQ or NMI, relax the xAPIC IPI test's assertion on the
> number of HLT exits to only require that the number of exits is less than
> or equal to the number of HLT instructions that were executed.  I.e. don't
> fail the test if Idle HLT does what it's supposed to do.
> 
> Note, unfortunately there's no way to determine if *KVM* supports Idle HLT,
> as this_cpu_has() checks raw CPU support, and kvm_cpu_has() checks what can
> be exposed to L1, i.e. the latter would check if KVM supports nested Idle
> HLT.  But, since the assert is purely bonus coverage, checking for CPU
> support is good enough.
> 
> Cc: Manali Shukla <Manali.Shukla@amd.com>
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> ---
>  tools/testing/selftests/kvm/include/x86/processor.h |  1 +
>  tools/testing/selftests/kvm/x86/xapic_ipi_test.c    | 13 ++++++++++++-
>  2 files changed, 13 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/testing/selftests/kvm/include/x86/processor.h b/tools/testing/selftests/kvm/include/x86/processor.h
> index 61578f038aff..32ab6ca7ec32 100644
> --- a/tools/testing/selftests/kvm/include/x86/processor.h
> +++ b/tools/testing/selftests/kvm/include/x86/processor.h
> @@ -200,6 +200,7 @@ struct kvm_x86_cpu_feature {
>  #define X86_FEATURE_PAUSEFILTER         KVM_X86_CPU_FEATURE(0x8000000A, 0, EDX, 10)
>  #define X86_FEATURE_PFTHRESHOLD         KVM_X86_CPU_FEATURE(0x8000000A, 0, EDX, 12)
>  #define	X86_FEATURE_VGIF		KVM_X86_CPU_FEATURE(0x8000000A, 0, EDX, 16)
> +#define X86_FEATURE_IDLE_HLT		KVM_X86_CPU_FEATURE(0x8000000A, 0, EDX, 30)
>  #define X86_FEATURE_SEV			KVM_X86_CPU_FEATURE(0x8000001F, 0, EAX, 1)
>  #define X86_FEATURE_SEV_ES		KVM_X86_CPU_FEATURE(0x8000001F, 0, EAX, 3)
>  #define	X86_FEATURE_PERFMON_V2		KVM_X86_CPU_FEATURE(0x80000022, 0, EAX, 0)
> diff --git a/tools/testing/selftests/kvm/x86/xapic_ipi_test.c b/tools/testing/selftests/kvm/x86/xapic_ipi_test.c
> index b255c7fbe519..35cb9de54a82 100644
> --- a/tools/testing/selftests/kvm/x86/xapic_ipi_test.c
> +++ b/tools/testing/selftests/kvm/x86/xapic_ipi_test.c
> @@ -466,7 +466,18 @@ int main(int argc, char *argv[])
>  	cancel_join_vcpu_thread(threads[0], params[0].vcpu);
>  	cancel_join_vcpu_thread(threads[1], params[1].vcpu);
>  
> -	TEST_ASSERT_EQ(data->hlt_count, vcpu_get_stat(params[0].vcpu, halt_exits));
> +	/*
> +	 * If the host support Idle HLT, i.e. KVM *might* be using Idle HLT,
> +	 * then the number of HLT exits may be less than the number of HLTs
> +	 * that were executed, as Idle HLT elides the exit if the vCPU has an
> +	 * unmasked, pending IRQ (or NMI).
> +	 */
> +	if (this_cpu_has(X86_FEATURE_IDLE_HLT))
> +		TEST_ASSERT(data->hlt_count >= vcpu_get_stat(params[0].vcpu, halt_exits),
> +			    "HLT insns = %lu, HLT exits = %lu",
> +			    data->hlt_count, vcpu_get_stat(params[0].vcpu, halt_exits));
> +	else
> +		TEST_ASSERT_EQ(data->hlt_count, vcpu_get_stat(params[0].vcpu, halt_exits));
>  
>  	fprintf(stderr,
>  		"Test successful after running for %d seconds.\n"
> 
> base-commit: fed48e2967f402f561d80075a20c5c9e16866e53


Tested on Genoa and Turin systems to cover both scenarios: CPU supports idle HLT intercept
and CPU doesn't support idle HLT intercept.

Tested-by: Manali Shukla <Manali.Shukla@amd.com>

Re: [PATCH] KVM: selftests: Relax assertion on HLT exits if CPU supports Idle HLT

[Sean Christopherson]

On Wed, 26 Feb 2025 15:18:09 -0800, Sean Christopherson wrote:
> If the CPU supports Idle HLT, which elides HLT VM-Exits if the vCPU has an
> unmasked pending IRQ or NMI, relax the xAPIC IPI test's assertion on the
> number of HLT exits to only require that the number of exits is less than
> or equal to the number of HLT instructions that were executed.  I.e. don't
> fail the test if Idle HLT does what it's supposed to do.
> 
> Note, unfortunately there's no way to determine if *KVM* supports Idle HLT,
> as this_cpu_has() checks raw CPU support, and kvm_cpu_has() checks what can
> be exposed to L1, i.e. the latter would check if KVM supports nested Idle
> HLT.  But, since the assert is purely bonus coverage, checking for CPU
> support is good enough.
> 
> [...]

Applied to kvm-x86 selftests, thanks!

[1/1] KVM: selftests: Relax assertion on HLT exits if CPU supports Idle HLT
      https://github.com/kvm-x86/linux/commit/62838fa5eade

--
https://github.com/kvm-x86/linux/tree/next