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Subject[PATCH v2 1/7] KVM: VMX: Restore host's MSR_IA32_RTIT_CTL when it's not zero
Date
A minor optimization to WRMSR MSR_IA32_RTIT_CTL when necessary.

Opportunistically refine the comment to call out that KVM requires
VM_EXIT_CLEAR_IA32_RTIT_CTL to expose PT to the guest.

Reviewed-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
---
Changes in v2:
- Refine comments
---
arch/x86/kvm/vmx/vmx.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index fada1055f325..5535a86aea37 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -1074,8 +1074,12 @@ static void pt_guest_exit(struct vcpu_vmx *vmx)
pt_load_msr(&vmx->pt_desc.host, vmx->pt_desc.addr_range);
}

- /* Reload host state (IA32_RTIT_CTL will be cleared on VM exit). */
- wrmsrl(MSR_IA32_RTIT_CTL, vmx->pt_desc.host.ctl);
+ /*
+ * KVM requires VM_EXIT_CLEAR_IA32_RTIT_CTL to expose PT to the guest,
+ * i.e. RTIT_CTL is always cleared on VM-Exit. Restore it if necessary.
+ */
+ if (vmx->pt_desc.host.ctl)
+ wrmsrl(MSR_IA32_RTIT_CTL, vmx->pt_desc.host.ctl);
}

void vmx_set_host_fs_gs(struct vmcs_host_state *host, u16 fs_sel, u16 gs_sel,
--
2.27.0
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