Commit 066941bd authored Jan 21, 2009 by H. Peter Anvin Committed by Ingo Molnar Jan 22, 2009

x86: unmask CPUID levels on Intel CPUs



Impact: Fixes crashes with misconfigured BIOSes on XSAVE hardware

Avuton Olrich reported early boot crashes with v2.6.28 and
bisected it down to dc1e35c6
("x86, xsave: enable xsave/xrstor on cpus with xsave support").

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.

Reported-and-bisected-by: Avuton Olrich <avuton@gmail.com>
Tested-by: Avuton Olrich <avuton@gmail.com>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>

parent bdf21a49

arch/x86/kernel/cpu/intel.c

+10 −0

Original line number	Diff line number	Diff line
		@@ -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);

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