From 31795b470b0872b66f7fa26f791b695c79821220 Mon Sep 17 00:00:00 2001 From: Boris Ostrovsky Date: Wed, 11 Feb 2015 14:39:18 -0500 Subject: [PATCH] x86/xen: Make sure X2APIC_ENABLE bit of MSR_IA32_APICBASE is not set Commit d524165cb8db ("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 Signed-off-by: David Vrabel --- arch/x86/xen/enlighten.c | 19 ++++++++++++++++++- 1 file changed, 18 insertions(+), 1 deletion(-) diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c index bd8b8459c3d0..efee14db009b 100644 --- a/arch/x86/xen/enlighten.c +++ b/arch/x86/xen/enlighten.c @@ -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, -- 2.20.1