Re: [PATCH kvm-unit-tests v2] memory: Skip tests for instructions that are absent

[Sean Christopherson <seanjc@google.com>]

On Mon, Apr 03, 2023, Paolo Bonzini wrote:
> Checking that instructions are absent is broken when running with CPU
> models other than the bare metal processor's, because neither VMX nor SVM have
> intercept controls for the instructions.
> 
> This can even happen with "-cpu max" when running under nested
> virtualization, which is the current situation in the Fedora KVM job
> on Cirrus-CI:
> 
> FAIL: clflushopt (ABSENT)
> FAIL: clwb (ABSENT)
> 
> In other words it looks like the features have been marked as disabled
> in the L0 host, while the hardware supports them.
> 
> Reported-by: Thomas Huth <thuth@redhat.com>
> Reviewed-by: Thomas Huth <thuth@redhat.com>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  x86/memory.c | 83 +++++++++++++++++++++++++++++++---------------------
>  1 file changed, 49 insertions(+), 34 deletions(-)
> 
> diff --git a/x86/memory.c b/x86/memory.c
> index 351e7c0..58ef835 100644
> --- a/x86/memory.c
> +++ b/x86/memory.c
> @@ -25,53 +25,68 @@ static void handle_ud(struct ex_regs *regs)
>  
>  int main(int ac, char **av)
>  {
> -	int expected;
> -
>  	handle_exception(UD_VECTOR, handle_ud);
>  
>  	/* 3-byte instructions: */
>  	isize = 3;

We can clean this up even further by utilizing TRY_ASM().  Though I think this is
a good excuse to add things like asm_safe(), asm_safe_report(), and asm_safe_report_ex(),
to cut down on the boilerplate even more.  I'll send patches on top.