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x86/xen: Make sure X2APIC_ENABLE bit of MSR_IA32_APICBASE is not set

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Commit d524165cb8 ("x86/apic: Check x2apic early") tests X2APIC_ENABLE
bit of MSR_IA32_APICBASE when CONFIG_X86_X2APIC is off and panics
the kernel when this bit is set.

Xen's PV guests will pass this MSR read to the hypervisor which will
return its version of the MSR, where this bit might be set. Make sure
we clear it before returning MSR value to the caller.

Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: David Vrabel <david.vrabel@citrix.com>
This commit is contained in:
Boris Ostrovsky 2015-02-11 14:39:18 -05:00 committed by David Vrabel
parent c517d838eb
commit 31795b470b
1 changed files with 18 additions and 1 deletions
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19
arch/x86/xen/enlighten.c
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@ -1070,6 +1070,23 @@ static inline void xen_write_cr8(unsigned long val)
BUG_ON(val);
}
#endif
static u64 xen_read_msr_safe(unsigned int msr, int *err)
{
u64 val;
val = native_read_msr_safe(msr, err);
switch (msr) {
case MSR_IA32_APICBASE:
#ifdef CONFIG_X86_X2APIC
if (!(cpuid_ecx(1) & (1 << (X86_FEATURE_X2APIC & 31))))
#endif
val &= ~X2APIC_ENABLE;
break;
}
return val;
}
static int xen_write_msr_safe(unsigned int msr, unsigned low, unsigned high)
{
int ret;
@ -1240,7 +1257,7 @@ static const struct pv_cpu_ops xen_cpu_ops __initconst = {
.wbinvd = native_wbinvd,
.read_msr = native_read_msr_safe,
.read_msr = xen_read_msr_safe,
.write_msr = xen_write_msr_safe,
.read_tsc = native_read_tsc,