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

[Oliver Upton <oupton@google.com>]

On Wed, Jan 22, 2020 at 10:47:28AM +0100, Vitaly Kuznetsov wrote:
> 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();
> 
> ?

Even better :) Thanks Vitaly!

> >  	test_set_guest(rdtsc_vmexit_diff_test_guest);
> >  
> >  	reset_guest_tsc_to_zero();
> 
> -- 
> Vitaly
>