Re: [PATCH 1/2] selftests: kvm: introduce cpu_has_svm() check

[Sean Christopherson <sean.j.christopherson@intel.com>]

On Fri, May 29, 2020 at 03:04:06PM +0200, Vitaly Kuznetsov wrote:
> More tests may want to check if the CPU is Intel or AMD in
> guest code, separate cpu_has_svm() and put it as static
> inline to svm_util.h.
> 
> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
> ---
>  tools/testing/selftests/kvm/include/x86_64/svm_util.h | 10 ++++++++++
>  tools/testing/selftests/kvm/x86_64/state_test.c       |  9 +--------
>  2 files changed, 11 insertions(+), 8 deletions(-)
> 
> diff --git a/tools/testing/selftests/kvm/include/x86_64/svm_util.h b/tools/testing/selftests/kvm/include/x86_64/svm_util.h
> index cd037917fece..b1057773206a 100644
> --- a/tools/testing/selftests/kvm/include/x86_64/svm_util.h
> +++ b/tools/testing/selftests/kvm/include/x86_64/svm_util.h
> @@ -35,4 +35,14 @@ void generic_svm_setup(struct svm_test_data *svm, void *guest_rip, void *guest_r
>  void run_guest(struct vmcb *vmcb, uint64_t vmcb_gpa);
>  void nested_svm_check_supported(void);
>  
> +static inline bool cpu_has_svm(void)
> +{
> +	u32 eax = 0x80000001, ecx;
> +
> +	asm volatile("cpuid" :
> +		     "=a" (eax), "=c" (ecx) : "0" (eax) : "ebx", "edx");

	u32 eax, ecx;

	asm("cpuid" : "=a" (eax), "=c" (ecx) : "a" (0x80000001) : "ebx", "edx");

The volatile shouldn't be needed, e.g. no one should be using this purely
for its seralization properties, and I don't see any reason to put the leaf
number into a variable.

Alternatively, adding a proper cpuid framework to processor.h would likely
be useful in the long run.

> +
> +	return ecx & CPUID_SVM;
> +}
> +