[PATCH v4 08/19] x86/cpu: Clear VMX feature flag if VMX is not fully enabled

Sean Christopherson
2019-11-28T01:41:48Z

Now that IA32_FEAT_CTL is always configured and locked for CPUs that are
known to support VMX[*], clear the VMX capability flag if the MSR is
unsupported or BIOS disabled VMX, i.e. locked IA32_FEAT_CTL and didn't
set the appropriate VMX enable bit.

[*] Because init_ia32_feat_ctl() is called from vendors ->c_init(), it's
still possible for IA32_FEAT_CTL to be left unlocked when VMX is
supported by the CPU. This is not fatal, and will be addressed in a
future patch.

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
---
arch/x86/kernel/cpu/feat_ctl.c | 23 ++++++++++++++++++++---
1 file changed, 20 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/cpu/feat_ctl.c b/arch/x86/kernel/cpu/feat_ctl.c
index c4f8f767853b..a46c9e46f937 100644
--- a/arch/x86/kernel/cpu/feat_ctl.c
+++ b/arch/x86/kernel/cpu/feat_ctl.c
@@ -5,15 +5,21 @@
#include <asm/msr-index.h>
#include <asm/processor.h>

+#undef pr_fmt
+#define pr_fmt(fmt) "x86/cpu: " fmt
+
void init_ia32_feat_ctl(struct cpuinfo_x86 *c)
{
+ bool tboot = tboot_enabled();
u64 msr;

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

if (msr & FEAT_CTL_LOCKED)
- return;
+ goto update_caps;

/*
* Ignore whatever value BIOS left in the MSR to avoid enabling random
@@ -29,9 +35,20 @@ void init_ia32_feat_ctl(struct cpuinfo_x86 *c)
if (cpu_has(c, X86_FEATURE_VMX) && IS_ENABLED(CONFIG_KVM_INTEL)) {
msr |= FEAT_CTL_VMX_ENABLED_OUTSIDE_SMX;

- if (tboot_enabled())
+ if (tboot)
msr |= FEAT_CTL_VMX_ENABLED_INSIDE_SMX;
}

wrmsrl(MSR_IA32_FEAT_CTL, msr);
+
+update_caps:
+ if (!cpu_has(c, X86_FEATURE_VMX))
+ return;
+
+ if ( (tboot && !(msr & FEAT_CTL_VMX_ENABLED_INSIDE_SMX)) ||
+ (!tboot && !(msr & FEAT_CTL_VMX_ENABLED_OUTSIDE_SMX))) {
+ pr_err_once("VMX (%s TXT) disabled by BIOS\n",
+ tboot ? "inside" : "outside");
+ clear_cpu_cap(c, X86_FEATURE_VMX);
+ }
}
--
2.24.0