[PATCH] KVM: selftests: Don't force -march=x86-64-v2 if it's unsupported

[PATCH] KVM: selftests: Don't force -march=x86-64-v2 if it's unsupported

[Sean Christopherson]

Force -march=x86-64-v2 to avoid SSE/AVX instructions if and only if the
uarch definition is supported by the compiler, e.g. gcc 7.5 only supports
x86-64.

Fixes: 9a400068a158 ("KVM: selftests: x86: Avoid using SSE/AVX instructions")
Cc: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
---

My big ol' AVX enabling series ain't looking so bad now ;-)

 tools/testing/selftests/kvm/Makefile | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/tools/testing/selftests/kvm/Makefile b/tools/testing/selftests/kvm/Makefile
index 156fbfae940f..5fa282643cff 100644
--- a/tools/testing/selftests/kvm/Makefile
+++ b/tools/testing/selftests/kvm/Makefile
@@ -249,8 +249,10 @@ ifeq ($(ARCH),s390)
 	CFLAGS += -march=z10
 endif
 ifeq ($(ARCH),x86)
+ifeq ($(shell echo "void foo(void) { }" | $(CC) -march=x86-64-v2 -x c - -c -o /dev/null 2>/dev/null; echo "$$?"),0)
 	CFLAGS += -march=x86-64-v2
 endif
+endif
 ifeq ($(ARCH),arm64)
 tools_dir := $(top_srcdir)/tools
 arm64_tools_dir := $(tools_dir)/arch/arm64/tools/

base-commit: 81983758430957d9a5cb3333fe324fd70cf63e7e
-- 
2.47.0.163.g1226f6d8fa-goog

Re: [PATCH] KVM: selftests: Don't force -march=x86-64-v2 if it's unsupported

[Vitaly Kuznetsov]

Sean Christopherson <seanjc@google.com> writes:

> Force -march=x86-64-v2 to avoid SSE/AVX instructions if and only if the
> uarch definition is supported by the compiler, e.g. gcc 7.5 only supports
> x86-64.
>
> Fixes: 9a400068a158 ("KVM: selftests: x86: Avoid using SSE/AVX instructions")
> Cc: Vitaly Kuznetsov <vkuznets@redhat.com>
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> ---
>
> My big ol' AVX enabling series ain't looking so bad now ;-)

Smaller the change, bigger the troubles :-)

>
>  tools/testing/selftests/kvm/Makefile | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/tools/testing/selftests/kvm/Makefile b/tools/testing/selftests/kvm/Makefile
> index 156fbfae940f..5fa282643cff 100644
> --- a/tools/testing/selftests/kvm/Makefile
> +++ b/tools/testing/selftests/kvm/Makefile
> @@ -249,8 +249,10 @@ ifeq ($(ARCH),s390)
>  	CFLAGS += -march=z10
>  endif
>  ifeq ($(ARCH),x86)
> +ifeq ($(shell echo "void foo(void) { }" | $(CC) -march=x86-64-v2 -x c - -c -o /dev/null 2>/dev/null; echo "$$?"),0)

With this test, the outer "ifeq ($(ARCH),x86)" check is not really
needed anymore I guess?

>  	CFLAGS += -march=x86-64-v2
>  endif
> +endif
>  ifeq ($(ARCH),arm64)
>  tools_dir := $(top_srcdir)/tools
>  arm64_tools_dir := $(tools_dir)/arch/arm64/tools/
>
> base-commit: 81983758430957d9a5cb3333fe324fd70cf63e7e

Reviewed-and-tested-by: Vitaly Kuznetsov <vkuznets@redhat.com>

-- 
Vitaly

Re: [PATCH] KVM: selftests: Don't force -march=x86-64-v2 if it's unsupported

[Sean Christopherson]

On Thu, Oct 31, 2024, Vitaly Kuznetsov wrote:
> > diff --git a/tools/testing/selftests/kvm/Makefile b/tools/testing/selftests/kvm/Makefile
> > index 156fbfae940f..5fa282643cff 100644
> > --- a/tools/testing/selftests/kvm/Makefile
> > +++ b/tools/testing/selftests/kvm/Makefile
> > @@ -249,8 +249,10 @@ ifeq ($(ARCH),s390)
> >  	CFLAGS += -march=z10
> >  endif
> >  ifeq ($(ARCH),x86)
> > +ifeq ($(shell echo "void foo(void) { }" | $(CC) -march=x86-64-v2 -x c - -c -o /dev/null 2>/dev/null; echo "$$?"),0)
> 
> With this test, the outer "ifeq ($(ARCH),x86)" check is not really
> needed anymore I guess?

Yeah, but at this point in the v6.12 cycle, I want to do the absolute bare minimum.
In 6.13, after the AVX support lands, I think we can/should revert this restriction,
i.e. it's a short-term wart.

Re: [PATCH] KVM: selftests: Don't force -march=x86-64-v2 if it's unsupported

[Sean Christopherson]

On Wed, 30 Oct 2024 21:53:33 -0700, Sean Christopherson wrote:
> Force -march=x86-64-v2 to avoid SSE/AVX instructions if and only if the
> uarch definition is supported by the compiler, e.g. gcc 7.5 only supports
> x86-64.

Applied to kvm-x86 fixes, thanks!

[1/1] KVM: selftests: Don't force -march=x86-64-v2 if it's unsupported
      https://github.com/kvm-x86/linux/commit/979956bc6811

--
https://github.com/kvm-x86/linux/tree/next