[RFC PATCH 2/4] KVM: x86: Add KVM exit for IOAPIC EOIs

[Steve Rutherford <srutherford@google.com>]

Adds KVM_EXIT_IOAPIC_EOI which passes the interrupt vector up to
userspace.

Uses a per VCPU exit bitmap to decide whether or not the IOAPIC needs
to be informed (which is identical to the EOI_EXIT_BITMAP field used
by modern x86 processors, but can also be used to elide kvm IOAPIC EOI
exits on older processors).

[Note: A prototype using ResampleFDs found that decoupling the EOI
from the VCPU's thread made it possible for the VCPU to not see a
recent EOI after reentering the guest. This does not match real
hardware.]

Compile tested for Intel x86.

Signed-off-by: Steve Rutherford <srutherford@google.com>
---
 Documentation/virtual/kvm/api.txt | 10 ++++++++++
 arch/x86/include/asm/kvm_host.h   |  3 +++
 arch/x86/kvm/lapic.c              |  9 +++++++++
 arch/x86/kvm/x86.c                | 11 +++++++++++
 include/linux/kvm_host.h          |  1 +
 include/uapi/linux/kvm.h          |  5 +++++
 6 files changed, 39 insertions(+)

diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
index 0744b4e..dd92996 100644
--- a/Documentation/virtual/kvm/api.txt
+++ b/Documentation/virtual/kvm/api.txt
@@ -3285,6 +3285,16 @@ Valid values for 'type' are:
 	 */
 	__u64 kvm_valid_regs;
 	__u64 kvm_dirty_regs;
+
+	/* KVM_EXIT_IOAPIC_EOI */
+        struct {
+	       __u8 vector;
+        } eoi;
+
+Indicates that an eoi of a level triggered IOAPIC interrupt on vector has
+occurred, which should be handled by the userspace IOAPIC. Triggers when
+the Irqchip has been split between userspace and the kernel.
+
 	union {
 		struct kvm_sync_regs regs;
 		char padding[1024];
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 3ddc134..b1978f1 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -539,6 +539,9 @@ struct kvm_vcpu_arch {
 	struct {
 		bool pv_unhalted;
 	} pv;
+
+	u64 eoi_exit_bitmaps[4];
+	int pending_ioapic_eoi;
 };
 
 struct kvm_lpage_info {
diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index bc392a6..42fada6f 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -860,6 +860,15 @@ int kvm_apic_compare_prio(struct kvm_vcpu *vcpu1, struct kvm_vcpu *vcpu2)
 
 static void kvm_ioapic_send_eoi(struct kvm_lapic *apic, int vector)
 {
+	if (irqchip_split(apic->vcpu->kvm)) {
+		if (test_bit(vector,
+			     (void *) apic->vcpu->arch.eoi_exit_bitmaps)) {
+			apic->vcpu->arch.pending_ioapic_eoi = vector;
+			kvm_make_request(KVM_REQ_IOAPIC_EOI_EXIT, apic->vcpu);
+		}
+		return;
+	}
+
 	if (kvm_ioapic_handles_vector(apic->vcpu->kvm, vector)) {
 		int trigger_mode;
 		if (apic_test_vector(vector, apic->regs + APIC_TMR))
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 7505b39..cc27c35 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -6324,6 +6324,17 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
 			kvm_handle_pmu_event(vcpu);
 		if (kvm_check_request(KVM_REQ_PMI, vcpu))
 			kvm_deliver_pmi(vcpu);
+		if (kvm_check_request(KVM_REQ_IOAPIC_EOI_EXIT, vcpu)) {
+			BUG_ON(vcpu->arch.pending_ioapic_eoi > 255);
+			if (test_bit(vcpu->arch.pending_ioapic_eoi,
+				     (void *) vcpu->arch.eoi_exit_bitmaps)) {
+				vcpu->run->exit_reason = KVM_EXIT_IOAPIC_EOI;
+				vcpu->run->eoi.vector =
+						vcpu->arch.pending_ioapic_eoi;
+				r = 0;
+				goto out;
+			}
+		}
 		if (kvm_check_request(KVM_REQ_SCAN_IOAPIC, vcpu))
 			vcpu_scan_ioapic(vcpu);
 		if (kvm_check_request(KVM_REQ_APIC_PAGE_RELOAD, vcpu))
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 277b7a1..cef20ad 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -134,6 +134,7 @@ static inline bool is_error_page(struct page *page)
 #define KVM_REQ_ENABLE_IBS        23
 #define KVM_REQ_DISABLE_IBS       24
 #define KVM_REQ_APIC_PAGE_RELOAD  25
+#define KVM_REQ_IOAPIC_EOI_EXIT   26
 
 #define KVM_USERSPACE_IRQ_SOURCE_ID		0
 #define KVM_IRQFD_RESAMPLE_IRQ_SOURCE_ID	1
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index 7d06dc4..2305948 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -183,6 +183,7 @@ struct kvm_s390_skeys {
 #define KVM_EXIT_EPR              23
 #define KVM_EXIT_SYSTEM_EVENT     24
 #define KVM_EXIT_S390_STSI        25
+#define KVM_EXIT_IOAPIC_EOI       26
 
 /* For KVM_EXIT_INTERNAL_ERROR */
 /* Emulate instruction failed. */
@@ -329,6 +330,10 @@ struct kvm_run {
 			__u8 sel1;
 			__u16 sel2;
 		} s390_stsi;
+		/* KVM_EXIT_IOAPIC_EOI */
+		struct {
+			__u8 vector;
+		} eoi;
 		/* Fix the size of the union. */
 		char padding[256];
 	};
-- 
2.2.0.rc0.207.ga3a616c