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

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Message-ID: <ZyO5ZUb8Acp80Ygq@google.com>
Date: Thu, 31 Oct 2024 10:07:49 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Vitaly Kuznetsov <vkuznets@...hat.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM: selftests: Don't force -march=x86-64-v2 if it's unsupported

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.