KVM: x86: hyper-v: Resurrect dedicated KVM_REQ_HV_TLB_FLUSH flag

In preparation to implementing fine-grained Hyper-V TLB flush and
L2 TLB flush, resurrect dedicated KVM_REQ_HV_TLB_FLUSH request bit. As
KVM_REQ_TLB_FLUSH_GUEST is a stronger operation, clear KVM_REQ_HV_TLB_FLUSH
request in kvm_vcpu_flush_tlb_guest().

The flush itself is temporary handled by kvm_vcpu_flush_tlb_guest().

No functional change intended.
Reviewed-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20221101145426.251680-9-vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/include/asm/kvm_host.h

@@ -110,6 +110,8 @@
 	KVM_ARCH_REQ_FLAGS(30, KVM_REQUEST_WAIT | KVM_REQUEST_NO_WAKEUP)
 #define KVM_REQ_MMU_FREE_OBSOLETE_ROOTS \
 	KVM_ARCH_REQ_FLAGS(31, KVM_REQUEST_WAIT | KVM_REQUEST_NO_WAKEUP)
+#define KVM_REQ_HV_TLB_FLUSH \
+	KVM_ARCH_REQ_FLAGS(32, KVM_REQUEST_WAIT | KVM_REQUEST_NO_WAKEUP)
 
 #define CR0_RESERVED_BITS                                               \
 	(~(unsigned long)(X86_CR0_PE | X86_CR0_MP | X86_CR0_EM | X86_CR0_TS \

arch/x86/kvm/hyperv.c

@@ -1870,11 +1870,11 @@ static u64 kvm_hv_flush_tlb(struct kvm_vcpu *vcpu, struct kvm_hv_hcall *hc)
 	 * analyze it here, flush TLB regardless of the specified address space.
 	 */
 	if (all_cpus) {
-		kvm_make_all_cpus_request(kvm, KVM_REQ_TLB_FLUSH_GUEST);
+		kvm_make_all_cpus_request(kvm, KVM_REQ_HV_TLB_FLUSH);
 	} else {
 		sparse_set_to_vcpu_mask(kvm, sparse_banks, valid_bank_mask, vcpu_mask);
 
-		kvm_make_vcpus_request_mask(kvm, KVM_REQ_TLB_FLUSH_GUEST, vcpu_mask);
+		kvm_make_vcpus_request_mask(kvm, KVM_REQ_HV_TLB_FLUSH, vcpu_mask);
 	}
 
 ret_success:

arch/x86/kvm/svm/svm.c

@@ -3722,6 +3722,13 @@ static void svm_flush_tlb_current(struct kvm_vcpu *vcpu)
 {
 	struct vcpu_svm *svm = to_svm(vcpu);
 
+	/*
+	 * Unlike VMX, SVM doesn't provide a way to flush only NPT TLB entries.
+	 * A TLB flush for the current ASID flushes both "host" and "guest" TLB
+	 * entries, and thus is a superset of Hyper-V's fine grained flushing.
+	 */
+	kvm_clear_request(KVM_REQ_HV_TLB_FLUSH, vcpu);
+
 	/*
 	 * Flush only the current ASID even if the TLB flush was invoked via
 	 * kvm_flush_remote_tlbs().  Although flushing remote TLBs requires all

arch/x86/kvm/x86.c

@@ -3420,6 +3420,12 @@ static void kvm_vcpu_flush_tlb_guest(struct kvm_vcpu *vcpu)
 	}
 
 	static_call(kvm_x86_flush_tlb_guest)(vcpu);
+
+	/*
+	 * Flushing all "guest" TLB is always a superset of Hyper-V's fine
+	 * grained flushing.
+	 */
+	kvm_clear_request(KVM_REQ_HV_TLB_FLUSH, vcpu);
 }
 
 
@@ -10250,6 +10256,9 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
 
 		kvm_service_local_tlb_flush_requests(vcpu);
 
+		if (kvm_check_request(KVM_REQ_HV_TLB_FLUSH, vcpu))
+			kvm_vcpu_flush_tlb_guest(vcpu);
+
 		if (kvm_check_request(KVM_REQ_REPORT_TPR_ACCESS, vcpu)) {
 			vcpu->run->exit_reason = KVM_EXIT_TPR_ACCESS;
 			r = 0;