linux-kernel - Re: [PATCH] KVM: x86: emulate SAHF instruction

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Message-ID: <20131031154707.GC20205@redhat.com>
Date:	Thu, 31 Oct 2013 17:47:07 +0200
From:	Gleb Natapov <gleb@...hat.com>
To:	Paolo Bonzini <pbonzini@...hat.com>
Cc:	linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	stable@...r.kernel.org
Subject: Re: [PATCH] KVM: x86: emulate SAHF instruction

On Thu, Oct 31, 2013 at 03:49:04PM +0100, Paolo Bonzini wrote:
> Il 31/10/2013 15:34, Gleb Natapov ha scritto:
> > I haven't checked AMD doc, but if it is documented that lahf/sahf #UDs at 64
> > bit we should emulate it correctly.
> 
> It says "The LAHF instruction can only be executed in 64-bit mode if
> supported by the processor implementation. Check the status of ECX bit 0
> returned by CPUID function 8000_0001h to verify that the processor
> supports LAHF in 64-bit mode".  Same as Intel---in fact 80000001h is an
> "AMD leaf" so to speak.
> 
> I found "AMD introduced support for the instructions with their Athlon
> 64, Opteron and Turion 64 revision D processors in March 2005 and Intel
> introduced support for the instructions with the Pentium 4 G1 stepping
> in December 2005".  I think we can for all practical purposes ignore the
> lahf_lm CPUID flag.
> 
Yep,

Reviewed-by: Gleb Natapov <gleb@...hat.com>

--
			Gleb.
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