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-rw-r--r--src/cpu/intel/model_206ax/model_206ax_init.c19
1 files changed, 16 insertions, 3 deletions
diff --git a/src/cpu/intel/model_206ax/model_206ax_init.c b/src/cpu/intel/model_206ax/model_206ax_init.c
index 64c32a0bc9..71879e2b1f 100644
--- a/src/cpu/intel/model_206ax/model_206ax_init.c
+++ b/src/cpu/intel/model_206ax/model_206ax_init.c
@@ -144,10 +144,23 @@ static void enable_vmx(void)
printk(BIOS_DEBUG, "%s VMX\n", enable ? "Enabling" : "Disabling");
+ /* Even though the Intel manual says you must set the lock bit in addition
+ * to the VMX bit in order for VMX to work, it is incorrect. Thus we leave
+ * it unlocked for the OS to manage things itself. This is good for a few
+ * reasons:
+ * - No need to reflash the bios just to toggle the lock bit.
+ * - The VMX bits really really should match each other across cores, so
+ * hard locking it on one while another has the opposite setting can
+ * easily lead to crashes as code using VMX migrates between them.
+ * - Vendors that want to "upsell" from a bios that disables+locks to
+ * one that doesn't is sleazy.
+ * By leaving this to the OS (e.g. Linux), people can do exactly what they
+ * want on the fly, and do it correctly (e.g. across multiple cores).
+ */
if (enable) {
- msr.lo |= (1 << 2);
- if (regs.ecx & CPUID_SMX)
- msr.lo |= (1 << 1);
+ msr.lo |= (1 << 2);
+ if (regs.ecx & CPUID_SMX)
+ msr.lo |= (1 << 1);
}
wrmsr(IA32_FEATURE_CONTROL, msr);