From: Paolo Bonzini <pbonzini@redhat.com>
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
Date: Thu, 31 Oct 2013 15:49:04 +0100 [thread overview]
Message-ID: <52726DE0.3060207@redhat.com> (raw)
In-Reply-To: <20131031143405.GT4651@redhat.com>
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
next prev parent reply other threads:[~2013-10-31 14:49 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-10-31 10:29 [PATCH] KVM: x86: emulate SAHF instruction Paolo Bonzini
2013-10-31 14:21 ` Gleb Natapov
2013-10-31 14:27 ` Paolo Bonzini
2013-10-31 14:34 ` Gleb Natapov
2013-10-31 14:49 ` Paolo Bonzini [this message]
2013-10-31 15:14 ` Borislav Petkov
2013-10-31 15:47 ` Gleb Natapov
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