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| author | Eduardo Habkost <ehabkost@redhat.com> | 2012-12-20 16:43:48 -0200 |
|---|---|---|
| committer | Anthony Liguori <aliguori@us.ibm.com> | 2012-12-23 09:11:24 -0600 |
| commit | 57f26ae72983095d0258e391041dfb8864f769e5 (patch) | |
| tree | c3e3d31d23769925ec536eaf5b5bc708dc17d2da /target-i386 | |
| parent | 586502189edf9fd0f89a83de96717a2ea826fdb0 (diff) | |
| download | qemu-57f26ae72983095d0258e391041dfb8864f769e5.tar.gz | |
target-i386: CPUID: return highest basic leaf if eax > cpuid_xlevel
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 = 05H (* Returns MONITOR/MWAIT leaf. *)
> CPUID.EAX = 0AH (* Returns Architectural Performance Monitoring leaf. *)
> CPUID.EAX = 0BH (* Returns Extended Topology Enumeration leaf. *)
> CPUID.EAX = 0CH (* INVALID: Returns the same information as CPUID.EAX = 0BH. *)
> CPUID.EAX = 80000008H (* Returns linear/physical address size data. *)
> CPUID.EAX = 8000000AH (* INVALID: Returns same information as CPUID.EAX = 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.
>
> • 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.
>
> • 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=cpuid_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 <ehabkost@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
Diffstat (limited to 'target-i386')
| -rw-r--r-- | target-i386/cpu.c | 6 |
1 files changed, 5 insertions, 1 deletions
diff --git a/target-i386/cpu.c b/target-i386/cpu.c index 1837f5af04..3cd1cee540 100644 --- a/target-i386/cpu.c +++ b/target-i386/cpu.c @@ -1648,7 +1648,11 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index, uint32_t count, index = env->cpuid_xlevel; } } else { - index = env->cpuid_xlevel; + /* Intel documentation states that invalid EAX input will + * return the same information as EAX=cpuid_level + * (Intel SDM Vol. 2A - Instruction Set Reference - CPUID) + */ + index = env->cpuid_level; } } } else { |