From 57f26ae72983095d0258e391041dfb8864f769e5 Mon Sep 17 00:00:00 2001
From: Eduardo Habkost <ehabkost@redhat.com>
Date: Thu, 20 Dec 2012 16:43:48 -0200
Subject: [PATCH] target-i386: CPUID: return highest basic leaf if eax >
cpuid_xlevel
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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>
---
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 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 {
--
2.30.2