snapshot: don't save MSR_IA32_BNDCFGS by default

The IA32_BNDCFGS MSR is only valid on Intel processors that support MPX
and only if MPX is enabled (CPUID.(EAX=07H, ECX=0H):EBX[14] = 1) and if
KVM supports it.
We only need to save this MSR if the Guest supports and uses MPX.
Otherwise a snapshotted Guest with MPX disabled will not be able to
resume on a different machine with a CPU that does not have MPX.
Saving this MSR should be done only if explicitly specified by the CPU
template or if the MPX feature is set in the Guest CPUID.

Signed-off-by: Alexandru-Cezar Sardan <[email protected]>

Author: Alexandru-Cezar Sardan

src/arch/src/x86_64/msr.rs

@@ -220,7 +220,6 @@ static ALLOWED_MSR_RANGES: &[MsrRange] = &[
     SINGLE_MSR!(MSR_TURBO_ACTIVATION_RATIO),
     SINGLE_MSR!(MSR_IA32_TSCDEADLINE),
     MSR_RANGE!(APIC_BASE_MSR, APIC_MSR_INDEXES),
-    SINGLE_MSR!(MSR_IA32_BNDCFGS),
     SINGLE_MSR!(MSR_KVM_WALL_CLOCK_NEW),
     SINGLE_MSR!(MSR_KVM_SYSTEM_TIME_NEW),
     SINGLE_MSR!(MSR_KVM_ASYNC_PF_EN),