Re: [PATCH v3 7/9] KVM: vmx/pmu: Add Arch LBR emulation and its VMCS field

Sean Christopherson
2021-03-03T20:56:08Z

On Wed, Mar 03, 2021, Like Xu wrote:
> New VMX controls bits for Arch LBR are added. When bit 21 in vmentry_ctrl
> is set, VM entry will write the value from the "Guest IA32_LBR_CTL" guest
> state field to IA32_LBR_CTL. When bit 26 in vmexit_ctrl is set, VM exit
> will clear IA32_LBR_CTL after the value has been saved to the "Guest
> IA32_LBR_CTL" guest state field.

...

> @@ -2529,7 +2532,8 @@ static __init int setup_vmcs_config(struct vmcs_config *vmcs_conf,
> VM_EXIT_LOAD_IA32_EFER |
> VM_EXIT_CLEAR_BNDCFGS |
> VM_EXIT_PT_CONCEAL_PIP |
> - VM_EXIT_CLEAR_IA32_RTIT_CTL;
> + VM_EXIT_CLEAR_IA32_RTIT_CTL |
> + VM_EXIT_CLEAR_IA32_LBR_CTL;

So, how does MSR_ARCH_LBR_CTL get restored on the host? What if the host wants
to keep _its_ LBR recording active while the guest is running?

> if (adjust_vmx_controls(min, opt, MSR_IA32_VMX_EXIT_CTLS,
> &_vmexit_control) < 0)
> return -EIO;
> @@ -2553,7 +2557,8 @@ static __init int setup_vmcs_config(struct vmcs_config *vmcs_conf,
> VM_ENTRY_LOAD_IA32_EFER |
> VM_ENTRY_LOAD_BNDCFGS |
> VM_ENTRY_PT_CONCEAL_PIP |
> - VM_ENTRY_LOAD_IA32_RTIT_CTL;
> + VM_ENTRY_LOAD_IA32_RTIT_CTL |
> + VM_ENTRY_LOAD_IA32_LBR_CTL;
> if (adjust_vmx_controls(min, opt, MSR_IA32_VMX_ENTRY_CTLS,
> &_vmentry_control) < 0)
> return -EIO;
> --
> 2.29.2
>