From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:46549) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Tmt5N-0001nV-B3 for qemu-devel@nongnu.org; Sun, 23 Dec 2012 16:27:55 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Tmt5K-0002wv-K7 for qemu-devel@nongnu.org; Sun, 23 Dec 2012 16:27:53 -0500 Received: from mail-oa0-f54.google.com ([209.85.219.54]:40104) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Tmt5K-0002wr-FX for qemu-devel@nongnu.org; Sun, 23 Dec 2012 16:27:50 -0500 Received: by mail-oa0-f54.google.com with SMTP id n9so6258590oag.41 for ; Sun, 23 Dec 2012 13:27:49 -0800 (PST) From: Anthony Liguori In-Reply-To: <1356029028-7356-1-git-send-email-ehabkost@redhat.com> References: <1356029028-7356-1-git-send-email-ehabkost@redhat.com> Date: Sun, 23 Dec 2012 15:27:47 -0600 Message-ID: <87a9t4tq5o.fsf@codemonkey.ws> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Subject: Re: [Qemu-devel] [PATCH] target-i386: CPUID: return highest basic leaf if eax > cpuid_xlevel List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Eduardo Habkost , qemu-devel@nongnu.org Cc: Marcelo Tosatti , Markus Armbruster , "brillywu@viatech.com.cn" Eduardo Habkost writes: > This fixes a subtle bug. A bug that probably won't cause trouble for any > existing OS, but a bug anyway: > > Intel SDM Volume 2, CPUID Instruction states: > >> Two types of information are returned: basic and extended function >> information. If a value entered for CPUID.EAX is higher than the maximum >> input value for basic or extended function for that processor then the >> data for the highest basic information leaf is returned. For example, >> using the Intel Core i7 processor, the following is true: >> >> CPUID.EAX =3D 05H (* Returns MONITOR/MWAIT leaf. *) >> CPUID.EAX =3D 0AH (* Returns Architectural Performance Monitoring leaf= . *) >> CPUID.EAX =3D 0BH (* Returns Extended Topology Enumeration leaf. *) >> CPUID.EAX =3D 0CH (* INVALID: Returns the same information as CPUID.EA= X =3D 0BH. *) >> CPUID.EAX =3D 80000008H (* Returns linear/physical address size data. = *) >> CPUID.EAX =3D 8000000AH (* INVALID: Returns same information as CPUID.= EAX =3D 0BH. *) > > AMD's CPUID Specification, on the other hand, is less specific: > >> The CPUID instruction supports two sets or ranges of functions, >> standard and extended. >> >> =E2=80=A2 The smallest function number of the standard function range is >> Fn0000_0000. The largest function num- ber of the standard function >> range, for a particular implementation, is returned in CPUID >> Fn0000_0000_EAX. >> >> =E2=80=A2 The smallest function number of the extended function range is >> Fn8000_0000. The largest function num- ber of the extended function >> range, for a particular implementation, is returned in CPUID >> Fn8000_0000_EAX. >> >> Functions that are neither standard nor extended are undefined and >> should not be relied upon. > > QEMU's behavior matched Intel's specification before, but this was > changed by commit b3baa152aaef1905876670590275c2dd0bbb088c. This patch > restores the behavior documented by Intel when cpuid_xlevel2 is 0. > > The existing behavior when cpuid_xlevel2 is set (falling back to > level=3Dcpuid_xlevel) is being kept, as I couldn't find any public > documentation on the CPUID 0xC0000000 function range on Centaur CPUs. > > Signed-off-by: Eduardo Habkost Applied. Thanks. Regards, Anthony Liguori > --- > Cc: Markus Armbruster > Cc: brillywu@viatech.com.cn > Cc: Marcelo Tosatti > --- > target-i386/cpu.c | 6 +++++- > 1 file changed, 5 insertions(+), 1 deletion(-) > > diff --git a/target-i386/cpu.c b/target-i386/cpu.c > index 1837f5a..3cd1cee 100644 > --- a/target-i386/cpu.c > +++ b/target-i386/cpu.c > @@ -1648,7 +1648,11 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t inde= x, uint32_t count, > index =3D env->cpuid_xlevel; > } > } else { > - index =3D env->cpuid_xlevel; > + /* Intel documentation states that invalid EAX input will > + * return the same information as EAX=3Dcpuid_level > + * (Intel SDM Vol. 2A - Instruction Set Reference - CPUI= D) > + */ > + index =3D env->cpuid_level; > } > } > } else { > --=20 > 1.7.11.7