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x86, cpu, amd: Fix WC+ workaround for older virtual hosts 

The WC+ workaround for F10h introduces a new MSR and kvm host #GPs
on accesses to unknown MSRs if paravirt is not compiled in. Use the
exception-handling MSR accessors so as not to break 3.8 and later guests
booting on older hosts.

Remove a redundant family check while at it.

Cc: Gleb Natapov <gleb@redhat.com>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: http://lkml.kernel.org/r/1361298793-31834-1-git-send-email-bp@alien8.de
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
This commit is contained in:
Borislav Petkov 2013-02-19 19:33:12 +01:00 committed by H. Peter Anvin
parent f0322bd341
commit 52d3d06e70
1 changed files with 7 additions and 5 deletions
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10
arch/x86/kernel/cpu/amd.c
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@ -723,12 +723,14 @@ static void __cpuinit init_amd(struct cpuinfo_x86 *c)
* performance degradation for certain nested-paging guests.
* Prevent this conversion by clearing bit 24 in
* MSR_AMD64_BU_CFG2.
*
* NOTE: we want to use the _safe accessors so as not to #GP kvm
* guests on older kvm hosts.
*/
if (c->x86 == 0x10) {
rdmsrl(MSR_AMD64_BU_CFG2, value);
rdmsrl_safe(MSR_AMD64_BU_CFG2, &value);
value &= ~(1ULL << 24);
wrmsrl(MSR_AMD64_BU_CFG2, value);
}
wrmsrl_safe(MSR_AMD64_BU_CFG2, value);
}
rdmsr_safe(MSR_AMD64_PATCH_LEVEL, &c->microcode, &dummy);