On 01/31/2018 05:55 PM, Paolo Bonzini wrote:
On 31/01/2018 11:50, Jim Mattson wrote:
+ if (to_vmx(vcpu)->save_spec_ctrl_on_exit) {
+ nested_vmx_disable_intercept_for_msr(
+ msr_bitmap_l1, msr_bitmap_l0,
+ MSR_IA32_PRED_CMD,
+ MSR_TYPE_R);
+ }
I don't think this should be predicated on
"to_vmx(vcpu)->save_spec_ctrl_on_exit." Why not just
"guest_cpuid_has(vcpu, X86_FEATURE_IBPB)"? Also, the final argument to
nested_vmx_disable_intercept_for_msr should be MSR_TYPE_W rather than
MSR_TYPE_R.
In fact this MSR can even be passed down unconditionally, since it needs
no save/restore and has no ill performance effect on the sibling
hyperthread.
Only MSR_IA32_SPEC_CTRL needs to be conditional on
"to_vmx(vcpu)->save_spec_ctrl_on_exit".
That used to be the case in an earlier version. There seems to be two
opinions here:
1) Pass it only if CPUID for the guest has it.
2) Pass it unconditionally.
I do not really have a preference.
Paolo
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