[PATCH] KVM: x86: Cleanup user space NMI injection

[Jan Kiszka <jan.kiszka@siemens.com>]

There is no point in doing the ready_for_nmi_injection/
request_nmi_window dance with user space. First, we don't do this for
in-kernel irqchip anyway, while the code path is the same as for user
space irqchip mode. And second, there is nothing to loose if a pending
NMI is overwritten by another one (in contrast to IRQs where we have to
save the number). Actually, there is even the risk of raising spurious
NMIs this way because the reason for the held-back NMI might already be
handled while processing the first one.

[ Avi, how to deal with the fields in struct kvm_run and the exit
reason? They are not mainline yet, neither in linux nor in qemu, and I
don't think they should ever be pushed in their current form. Simply
revert them? ]

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
---

 arch/x86/kvm/vmx.c  |   24 ++----------------------
 arch/x86/kvm/x86.c  |   34 ++++++++--------------------------
 include/linux/kvm.h |    6 +++---
 3 files changed, 13 insertions(+), 51 deletions(-)

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 775a140..6fbff55 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -2498,15 +2498,13 @@ static void do_interrupt_requests(struct kvm_vcpu *vcpu,
 	}
 	if (vcpu->arch.nmi_injected) {
 		vmx_inject_nmi(vcpu);
-		if (vcpu->arch.nmi_pending || kvm_run->request_nmi_window)
+		if (vcpu->arch.nmi_pending)
 			enable_nmi_window(vcpu);
 		else if (vcpu->arch.irq_summary
 			 || kvm_run->request_interrupt_window)
 			enable_irq_window(vcpu);
 		return;
 	}
-	if (!vcpu->arch.nmi_window_open || kvm_run->request_nmi_window)
-		enable_nmi_window(vcpu);
 
 	if (vcpu->arch.interrupt_window_open) {
 		if (vcpu->arch.irq_summary && !vcpu->arch.interrupt.pending)
@@ -3040,14 +3038,6 @@ static int handle_nmi_window(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
 	vmcs_write32(CPU_BASED_VM_EXEC_CONTROL, cpu_based_vm_exec_control);
 	++vcpu->stat.nmi_window_exits;
 
-	/*
-	 * If the user space waits to inject a NMI, exit as soon as possible
-	 */
-	if (kvm_run->request_nmi_window && !vcpu->arch.nmi_pending) {
-		kvm_run->exit_reason = KVM_EXIT_NMI_WINDOW_OPEN;
-		return 0;
-	}
-
 	return 1;
 }
 
@@ -3162,7 +3152,7 @@ static int kvm_handle_exit(struct kvm_run *kvm_run, struct kvm_vcpu *vcpu)
 			vmx->soft_vnmi_blocked = 0;
 			vcpu->arch.nmi_window_open = 1;
 		} else if (vmx->vnmi_blocked_time > 1000000000LL &&
-		    (kvm_run->request_nmi_window || vcpu->arch.nmi_pending)) {
+			   vcpu->arch.nmi_pending) {
 			/*
 			 * This CPU don't support us in finding the end of an
 			 * NMI-blocked window if the guest runs with IRQs
@@ -3175,16 +3165,6 @@ static int kvm_handle_exit(struct kvm_run *kvm_run, struct kvm_vcpu *vcpu)
 			vmx->soft_vnmi_blocked = 0;
 			vmx->vcpu.arch.nmi_window_open = 1;
 		}
-
-		/*
-		 * If the user space waits to inject an NNI, exit ASAP
-		 */
-		if (vcpu->arch.nmi_window_open && kvm_run->request_nmi_window
-		    && !vcpu->arch.nmi_pending) {
-			kvm_run->exit_reason = KVM_EXIT_NMI_WINDOW_OPEN;
-			++vcpu->stat.nmi_window_exits;
-			return 0;
-		}
 	}
 
 	if (exit_reason < kvm_vmx_max_exit_handlers
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 7a2aeba..a5da129 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2885,37 +2885,18 @@ static int dm_request_for_irq_injection(struct kvm_vcpu *vcpu,
 		(kvm_x86_ops->get_rflags(vcpu) & X86_EFLAGS_IF));
 }
 
-/*
- * Check if userspace requested a NMI window, and that the NMI window
- * is open.
- *
- * No need to exit to userspace if we already have a NMI queued.
- */
-static int dm_request_for_nmi_injection(struct kvm_vcpu *vcpu,
-					struct kvm_run *kvm_run)
-{
-	return (!vcpu->arch.nmi_pending &&
-		kvm_run->request_nmi_window &&
-		vcpu->arch.nmi_window_open);
-}
-
 static void post_kvm_run_save(struct kvm_vcpu *vcpu,
 			      struct kvm_run *kvm_run)
 {
 	kvm_run->if_flag = (kvm_x86_ops->get_rflags(vcpu) & X86_EFLAGS_IF) != 0;
 	kvm_run->cr8 = kvm_get_cr8(vcpu);
 	kvm_run->apic_base = kvm_get_apic_base(vcpu);
-	if (irqchip_in_kernel(vcpu->kvm)) {
+	if (irqchip_in_kernel(vcpu->kvm))
 		kvm_run->ready_for_interrupt_injection = 1;
-		kvm_run->ready_for_nmi_injection = 1;
-	} else {
+	else
 		kvm_run->ready_for_interrupt_injection =
 					(vcpu->arch.interrupt_window_open &&
 					 vcpu->arch.irq_summary == 0);
-		kvm_run->ready_for_nmi_injection =
-					(vcpu->arch.nmi_window_open &&
-					 vcpu->arch.nmi_pending == 0);
-	}
 }
 
 static void vapic_enter(struct kvm_vcpu *vcpu)
@@ -3091,11 +3072,6 @@ static int __vcpu_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
 		}
 
 		if (r > 0) {
-			if (dm_request_for_nmi_injection(vcpu, kvm_run)) {
-				r = -EINTR;
-				kvm_run->exit_reason = KVM_EXIT_NMI;
-				++vcpu->stat.request_nmi_exits;
-			}
 			if (dm_request_for_irq_injection(vcpu, kvm_run)) {
 				r = -EINTR;
 				kvm_run->exit_reason = KVM_EXIT_INTR;
@@ -4086,6 +4062,12 @@ int kvm_arch_vcpu_init(struct kvm_vcpu *vcpu)
 			goto fail_mmu_destroy;
 	}
 
+	/*
+	 * This interface is obsolete - we can always accept NMI requests
+	 * from user space as there is only a single channel involved.
+	 */
+	vcpu->run->ready_for_nmi_injection = 1;
+
 	return 0;
 
 fail_mmu_destroy:
diff --git a/include/linux/kvm.h b/include/linux/kvm.h
index 44fd7fa..f60bb55 100644
--- a/include/linux/kvm.h
+++ b/include/linux/kvm.h
@@ -84,20 +84,20 @@ struct kvm_irqchip {
 #define KVM_EXIT_S390_RESET       14
 #define KVM_EXIT_DCR              15
 #define KVM_EXIT_NMI              16
-#define KVM_EXIT_NMI_WINDOW_OPEN  17
+#define KVM_EXIT_NMI_WINDOW_OPEN  17	/* obsolete, no longer returned */
 
 /* for KVM_RUN, returned by mmap(vcpu_fd, offset=0) */
 struct kvm_run {
 	/* in */
 	__u8 request_interrupt_window;
-	__u8 request_nmi_window;
+	__u8 request_nmi_window;	/* obsolete, ignored */
 	__u8 padding1[6];
 
 	/* out */
 	__u32 exit_reason;
 	__u8 ready_for_interrupt_injection;
 	__u8 if_flag;
-	__u8 ready_for_nmi_injection;
+	__u8 ready_for_nmi_injection;	/* obsolete, always true */
 	__u8 padding2;
 
 	/* in (pre_kvm_run), out (post_kvm_run) */