[PATCH 2/3] x86/cpu: Mark SGX and VMX as being dependent on MSR_IA32_FEAT_CTL

Sean Christopherson
2022-12-03T00:40:38Z

Mark SGX and VMX as being dependent on MSR_IA32_FEAT_CTL now that CPUID
dependencies are processed unconditionally, i.e. now that SGX and VMX
will be disabled if MSR_IA32_FEAT_CTL is unsupported even if the kernel
never explicitly disables MSR_IA32_FEAT_CTL. Since init_ia32_feat_ctl()
is invoked if and only if the CPU might possibly support the MSR and the
kernel was built with the necessary CPU_SUP_*=y, it's possible for a CPU
that supports VMX and/or SGX to run on a kernel that never sets the
feature flag.

Explicitly clear MSR_IA32_FEAT_CTL if reading the MSR faults to handle
the extremely unlikely edge case where the RDMSR fails when restoring CPU
state after suspend, hibernate, kexec, etc.

Capturing the SGX and VMX dependencies will allow dropping manual checks
on X86_FEATURE_MSR_IA32_FEAT_CTL for code that just wants to detect if
SGX or VMX is fully supported.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
arch/x86/kernel/cpu/cpuid-deps.c | 2 ++
arch/x86/kernel/cpu/feat_ctl.c | 3 +--
2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/cpu/cpuid-deps.c b/arch/x86/kernel/cpu/cpuid-deps.c
index 68e26d4c8063..37abdb6fb4ea 100644
--- a/arch/x86/kernel/cpu/cpuid-deps.c
+++ b/arch/x86/kernel/cpu/cpuid-deps.c
@@ -72,6 +72,8 @@ static const struct cpuid_dep cpuid_deps[] = {
{ X86_FEATURE_AVX512_FP16, X86_FEATURE_AVX512BW },
{ X86_FEATURE_ENQCMD, X86_FEATURE_XSAVES },
{ X86_FEATURE_PER_THREAD_MBA, X86_FEATURE_MBA },
+ { X86_FEATURE_VMX, X86_FEATURE_MSR_IA32_FEAT_CTL },
+ { X86_FEATURE_SGX, X86_FEATURE_MSR_IA32_FEAT_CTL },
{ X86_FEATURE_SGX_LC, X86_FEATURE_SGX },
{ X86_FEATURE_SGX1, X86_FEATURE_SGX },
{ X86_FEATURE_SGX2, X86_FEATURE_SGX1 },
diff --git a/arch/x86/kernel/cpu/feat_ctl.c b/arch/x86/kernel/cpu/feat_ctl.c
index 03851240c3e3..0b7186d9ba05 100644
--- a/arch/x86/kernel/cpu/feat_ctl.c
+++ b/arch/x86/kernel/cpu/feat_ctl.c
@@ -117,8 +117,7 @@ void init_ia32_feat_ctl(struct cpuinfo_x86 *c)
u64 msr;

if (rdmsrl_safe(MSR_IA32_FEAT_CTL, &msr)) {
- clear_cpu_cap(c, X86_FEATURE_VMX);
- clear_cpu_cap(c, X86_FEATURE_SGX);
+ clear_cpu_cap(c, X86_FEATURE_MSR_IA32_FEAT_CTL);
return;
}

--
2.39.0.rc0.267.gcb52ba06e7-goog