[PATCH] x86: unmask CPUID levels on Intel CPUs

[H . Peter Anvin]

Impact: Fixes crashes with misconfigured BIOSes on XSAVE hardware

If the CPUID limit bit in MSR_IA32_MISC_ENABLE is set, clear it to
make all CPUID information available.  This is required for some
features to work, in particular XSAVE.

Signed-off-by: H. Peter Anvin <hpa@xxxxxxxxxxxxxxx>
---
 arch/x86/kernel/cpu/intel.c |   10 ++++++++++
 1 files changed, 10 insertions(+), 0 deletions(-)

diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
index 8ea6929..43c1dcf 100644
--- a/arch/x86/kernel/cpu/intel.c
+++ b/arch/x86/kernel/cpu/intel.c
@@ -29,6 +29,16 @@
 
 static void __cpuinit early_init_intel(struct cpuinfo_x86 *c)
 {
+	u64 misc_enable;
+
+	/* Unmask CPUID levels if masked */
+	if (!rdmsrl_safe(MSR_IA32_MISC_ENABLE, &misc_enable) &&
+	    (misc_enable & MSR_IA32_MISC_ENABLE_LIMIT_CPUID)) {
+		misc_enable &= ~MSR_IA32_MISC_ENABLE_LIMIT_CPUID;
+		wrmsrl(MSR_IA32_MISC_ENABLE, misc_enable);
+		c->cpuid_level = cpuid_eax(0);
+	}
+
 	if ((c->x86 == 0xf && c->x86_model >= 0x03) ||
 		(c->x86 == 0x6 && c->x86_model >= 0x0e))
 		set_cpu_cap(c, X86_FEATURE_CONSTANT_TSC);
-- 
1.6.0.6


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