Re: [PATCH v11 14/16] KVM: x86/vmx: Flip Arch LBREn bit on guest state change

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On 5/11/22 09:43, Yang, Weijiang wrote:

Instead of using flip_arch_lbr_ctl, SMM should save the value of the MSR
in kvm_x86_ops->enter_smm, and restore it in kvm_x86_ops->leave_smm
(feel free to do it only if guest_cpuid_has(vcpu, X86_FEATURE_LM), i.e.
the 32-bit case can be ignored).

In the case of migration in SMM, I assume kvm_x86_ops->enter_smm() called in source side

and kvm_x86_ops->leave_smm() is called at destination, then should the saved LBREn be transferred

to destination too? The destination can rely on the bit to defer setting LBREn bit in

Hi, it's transferred automatically if the MSR is saved in the SMM save state area. Both enter_smm and leave_smm can access the save state area.

The enter_smm callback is called after saving "normal" state, and it has to save the state + clear the bit; likewise, the leave_smm callback is called before saving "normal" state and will restore the old value of the MSR.

Thanks,

Paolo

VMCS until kvm_x86_ops->leave_smm() is called. is it good? thanks!




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