Re: [kvm-unit-tests PATCH] x86: VMX: Check preconditions for RDTSC test

[Vitaly Kuznetsov <vkuznets@redhat.com>]

Oliver Upton <oupton@google.com> writes:

> The RDTSC VM-exit test requires the 'use TSC offsetting' processor-based
> VM-execution control be allowed on the host. Check this precondition
> before running the test rather than asserting it later on to avoid
> erroneous failures on a host without TSC offsetting.
>
> Cc: Aaron Lewis <aaronlewis@google.com>
> Signed-off-by: Oliver Upton <oupton@google.com>
> ---
>  x86/vmx_tests.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/x86/vmx_tests.c b/x86/vmx_tests.c
> index 3b150323b325..de9a931216e2 100644
> --- a/x86/vmx_tests.c
> +++ b/x86/vmx_tests.c
> @@ -9161,9 +9161,6 @@ static void vmx_vmcs_shadow_test(void)
>   */
>  static void reset_guest_tsc_to_zero(void)
>  {
> -	TEST_ASSERT_MSG(ctrl_cpu_rev[0].clr & CPU_USE_TSC_OFFSET,
> -			"Expected support for 'use TSC offsetting'");
> -
>  	vmcs_set_bits(CPU_EXEC_CTRL0, CPU_USE_TSC_OFFSET);
>  	vmcs_write(TSC_OFFSET, -rdtsc());
>  }
> @@ -9210,6 +9207,11 @@ static void rdtsc_vmexit_diff_test(void)
>  	int fail = 0;
>  	int i;
>  
> +	if (!(ctrl_cpu_rev[0].clr & CPU_USE_TSC_OFFSET)) {
> +		printf("CPU doesn't support the 'use TSC offsetting' processor-based VM-execution control.\n");
> +		return;
> +	}
> +

Can we use test_skip() instead, something like

diff --git a/x86/vmx_tests.c b/x86/vmx_tests.c
index dd32b3aef08b..bfecf36d37ef 100644
--- a/x86/vmx_tests.c
+++ b/x86/vmx_tests.c
@@ -9166,6 +9166,9 @@ static void rdtsc_vmexit_diff_test(void)
        int fail = 0;
        int i;
 
+       if (!(ctrl_cpu_rev[0].clr & CPU_USE_TSC_OFFSET))
+               test_skip("CPU doesn't support the 'use TSC offsetting' processor-based VM-execution control.\n");
+
        test_set_guest(rdtsc_vmexit_diff_test_guest);
 
        reset_guest_tsc_to_zero();

?

>  	test_set_guest(rdtsc_vmexit_diff_test_guest);
>  
>  	reset_guest_tsc_to_zero();

-- 
Vitaly