Message-ID: <52726DE0.3060207@redhat.com>
Date: Thu, 31 Oct 2013 15:49:04 +0100
From: Paolo Bonzini <pbonzini@redhat.com>
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130923 Thunderbird/17.0.9
MIME-Version: 1.0
To: Gleb Natapov <gleb@redhat.com>
CC: linux-kernel@vger.kernel.org, kvm@vger.kernel.org, stable@vger.kernel.org
Subject: Re: [PATCH] KVM: x86: emulate SAHF instruction
References: <1383215382-10072-1-git-send-email-pbonzini@redhat.com> <20131031142119.GS4651@redhat.com> <527268E4.2070505@redhat.com> <20131031143405.GT4651@redhat.com>
In-Reply-To: <20131031143405.GT4651@redhat.com>
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1147
Lines: 28

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.

> Who knows what code depends on it.
> Of course I pretty much doubt we will ever emulate sahf in 64 bit mode

Yep.

Paolo

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/