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x86/cpufeatures: Disentangle MSR_SPEC_CTRL enumeration from IBRS

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The availability of the SPEC_CTRL MSR is enumerated by a CPUID bit on
Intel and implied by IBRS or STIBP support on AMD. That's just confusing
and in case an AMD CPU has IBRS not supported because the underlying
problem has been fixed but has another bit valid in the SPEC_CTRL MSR,
the thing falls apart.

Add a synthetic feature bit X86_FEATURE_MSR_SPEC_CTRL to denote the
availability on both Intel and AMD.

While at it replace the boot_cpu_has() checks with static_cpu_has() where
possible. This prevents late microcode loading from exposing SPEC_CTRL, but
late loading is already very limited as it does not reevaluate the
mitigation options and other bits and pieces. Having static_cpu_has() is
the simplest and least fragile solution.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
This commit is contained in:
Thomas Gleixner
2018-05-10 19:13:18 +02:00
parent e7c587da12
commit 7eb8956a7f
4 changed files with 20 additions and 9 deletions
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9
arch/x86/kernel/cpu/common.c
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@@ -761,19 +761,24 @@ static void init_speculation_control(struct cpuinfo_x86 *c)
if (cpu_has(c, X86_FEATURE_SPEC_CTRL)) {
set_cpu_cap(c, X86_FEATURE_IBRS);
set_cpu_cap(c, X86_FEATURE_IBPB);
set_cpu_cap(c, X86_FEATURE_MSR_SPEC_CTRL);
}
if (cpu_has(c, X86_FEATURE_INTEL_STIBP))
set_cpu_cap(c, X86_FEATURE_STIBP);
if (cpu_has(c, X86_FEATURE_AMD_IBRS))
if (cpu_has(c, X86_FEATURE_AMD_IBRS)) {
set_cpu_cap(c, X86_FEATURE_IBRS);
set_cpu_cap(c, X86_FEATURE_MSR_SPEC_CTRL);
}
if (cpu_has(c, X86_FEATURE_AMD_IBPB))
set_cpu_cap(c, X86_FEATURE_IBPB);
if (cpu_has(c, X86_FEATURE_AMD_STIBP))
if (cpu_has(c, X86_FEATURE_AMD_STIBP)) {
set_cpu_cap(c, X86_FEATURE_STIBP);
set_cpu_cap(c, X86_FEATURE_MSR_SPEC_CTRL);
}
}
void get_cpu_cap(struct cpuinfo_x86 *c)