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SubjectRe: [PATCH 2/2] selftests/x86/amx: Fix the test to avoid failure when AMX is unavailable
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On 4/1/22 4:10 PM, Chang S. Bae wrote:
> When a CPU does not have AMX, the test fails. But this is wrong as it
> should be runnable regardless. Skip the test instead.
>
> Reported-by: Thomas Gleixner <tglx@linutronix.de>
> Fixes: 6a3e0651b4a ("selftests/x86/amx: Add test cases for AMX state management")
> Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
> Cc: linux-kselftest@vger.kernel.org
> Cc: linux-kernel@vger.kernel.org
> ---
> tools/testing/selftests/x86/amx.c | 42 +++++++++++++++++++++++--------
> 1 file changed, 31 insertions(+), 11 deletions(-)
>
> diff --git a/tools/testing/selftests/x86/amx.c b/tools/testing/selftests/x86/amx.c
> index 3615ef4a48bb..14abb6072a7d 100644
> --- a/tools/testing/selftests/x86/amx.c
> +++ b/tools/testing/selftests/x86/amx.c
> @@ -106,6 +106,12 @@ static void clearhandler(int sig)
>
> #define CPUID_LEAF1_ECX_XSAVE_MASK (1 << 26)
> #define CPUID_LEAF1_ECX_OSXSAVE_MASK (1 << 27)
> +
> +static struct {
> + unsigned xsave: 1;
> + unsigned osxsave: 1;
> +} cpuinfo;
> +

Why is this needed? Also naming this cpuinfo is confuing.

> static inline void check_cpuid_xsave(void)
> {
> uint32_t eax, ebx, ecx, edx;
> @@ -118,10 +124,8 @@ static inline void check_cpuid_xsave(void)
> eax = 1;
> ecx = 0;
> cpuid(&eax, &ebx, &ecx, &edx);
> - if (!(ecx & CPUID_LEAF1_ECX_XSAVE_MASK))
> - fatal_error("cpuid: no CPU xsave support");
> - if (!(ecx & CPUID_LEAF1_ECX_OSXSAVE_MASK))
> - fatal_error("cpuid: no OS xsave support");
> + cpuinfo.xsave = !!(ecx & CPUID_LEAF1_ECX_XSAVE_MASK);
> + cpuinfo.osxsave = !!(ecx & CPUID_LEAF1_ECX_OSXSAVE_MASK);

Why add this complexity. Why not just Skip here?

> }
>
> static uint32_t xbuf_size;
> @@ -161,14 +165,31 @@ static void check_cpuid_xtiledata(void)
> * eax: XTILEDATA state component size
> * ebx: XTILEDATA state component offset in user buffer
> */
> - if (!eax || !ebx)
> - fatal_error("xstate cpuid: invalid tile data size/offset: %d/%d",
> - eax, ebx);
> -
> xtiledata.size = eax;
> xtiledata.xbuf_offset = ebx;
> }
>
> +static bool amx_available(void)
> +{
> + check_cpuid_xsave();
> + if (!cpuinfo.xsave) {
> + printf("[SKIP]\tcpuid: no CPU xsave support\n");
> + return false;
> + } else if (!cpuinfo.osxsave) {
> + printf("[SKIP]\tcpuid: no OS xsave support\n");
> + return false;
> + }
> +
> + check_cpuid_xtiledata();
> + if (!xtiledata.size || !xtiledata.xbuf_offset) {
> + printf("[SKIP]\txstate cpuid: no tile data (size/offset: %d/%d)\n",
> + xtiledata.size, xtiledata.xbuf_offset);
> + return false;
> + }
> +
> + return true;
> +}
> +

I am not seeing any value in adding this layer of abstraction.
Keep it simple and do the handling in main()

> /* The helpers for managing XSAVE buffer and tile states: */
>
> struct xsave_buffer *alloc_xbuf(void)
> @@ -826,9 +847,8 @@ static void test_context_switch(void)
>
> int main(void)
> {
> - /* Check hardware availability at first */
> - check_cpuid_xsave();
> - check_cpuid_xtiledata();
> + if (!amx_available())
> + return 0;

This should KSFT_SKIP for this to be reported as a skip. Returning 0
will be reported as a Pass.

>
> init_stashed_xsave();
> sethandler(SIGILL, handle_noperm, 0);
>

thanks,
-- Shuah

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