[PATCH 4/4] KVM/x86: Add tlb_remote_flush callback support for vmcs

[Tianyu Lan]

Register tlb_remote_flush callback for vmcs when hyperv capability of
nested guest mapping flush is detected. The interface can help to
reduce overhead when flush ept table among vcpus for nested VM. The
tradition way is to send IPIs to all affected vcpus and executes
INVEPT on each vcpus. It will trigger several vmexits for IPI
and INVEPT emulation. Hyper-V provides such hypercall to do
flush for all vcpus.

Signed-off-by: Lan Tianyu <Tianyu.Lan@xxxxxxxxxxxxx>
---
 arch/x86/kvm/vmx.c | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 0b1e4e9fef2b..e42ed4833983 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -4778,6 +4778,25 @@ static inline void __vmx_flush_tlb(struct kvm_vcpu *vcpu, int vpid,
 	}
 }
 
+static int hv_remote_flush_tlb(struct kvm *kvm)
+{
+	int ret;
+
+	spin_lock(&to_kvm_vmx(kvm)->ept_pointer_lock);
+
+	if (!VALID_PAGE(to_kvm_vmx(kvm)->identical_ept_pointer)) {
+		ret = -EFAULT;
+		goto out;
+	}
+
+	ret = hyperv_flush_guest_mapping(
+			to_kvm_vmx(kvm)->identical_ept_pointer);
+
+out:
+	spin_unlock(&to_kvm_vmx(kvm)->ept_pointer_lock);
+	return ret;
+}
+
 static void vmx_flush_tlb(struct kvm_vcpu *vcpu, bool invalidate_gpa)
 {
 	__vmx_flush_tlb(vcpu, to_vmx(vcpu)->vpid, invalidate_gpa);
@@ -7567,6 +7586,12 @@ static __init int hardware_setup(void)
 	if (enable_ept && !cpu_has_vmx_ept_2m_page())
 		kvm_disable_largepages();
 
+#if IS_ENABLED(CONFIG_HYPERV)
+	if (ms_hyperv.nested_features & HV_X64_NESTED_GUEST_MAPPING_FLUSH
+	    && enable_ept)
+		kvm_x86_ops->tlb_remote_flush = hv_remote_flush_tlb;
+#endif
+
 	if (!cpu_has_vmx_ple()) {
 		ple_gap = 0;
 		ple_window = 0;
-- 
2.14.3