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authorEduardo Habkost <ehabkost@redhat.com>2012-12-20 16:43:48 -0200
committerAnthony Liguori <aliguori@us.ibm.com>2012-12-23 09:11:24 -0600
commit57f26ae72983095d0258e391041dfb8864f769e5 (patch)
treec3e3d31d23769925ec536eaf5b5bc708dc17d2da /target-lm32/helper.c
parent586502189edf9fd0f89a83de96717a2ea826fdb0 (diff)
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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-lm32/helper.c')
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