KVM: selftests: Add utilities to create eventfds and do KVM_IRQFD

Add helpers to create eventfds and to (de)assign eventfds via KVM_IRQFD.

Tested-by: K Prateek Nayak <kprateek.nayak@amd.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20250522235223.3178519-13-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

Author: sean-jc

tools/testing/selftests/kvm/arm64/vgic_irq.c

@@ -620,18 +620,12 @@ static void kvm_routing_and_irqfd_check(struct kvm_vm *vm,
 	 * that no actual interrupt was injected for those cases.
 	 */
 
-	for (f = 0, i = intid; i < (uint64_t)intid + num; i++, f++) {
-		fd[f] = eventfd(0, 0);
-		TEST_ASSERT(fd[f] != -1, __KVM_SYSCALL_ERROR("eventfd()", fd[f]));
-	}
+	for (f = 0, i = intid; i < (uint64_t)intid + num; i++, f++)
+		fd[f] = kvm_new_eventfd();
 
 	for (f = 0, i = intid; i < (uint64_t)intid + num; i++, f++) {
-		struct kvm_irqfd irqfd = {
-			.fd  = fd[f],
-			.gsi = i - MIN_SPI,
-		};
 		assert(i <= (uint64_t)UINT_MAX);
-		vm_ioctl(vm, KVM_IRQFD, &irqfd);
+		kvm_assign_irqfd(vm, i - MIN_SPI, fd[f]);
 	}
 
 	for (f = 0, i = intid; i < (uint64_t)intid + num; i++, f++) {

tools/testing/selftests/kvm/include/kvm_util.h

@@ -18,6 +18,7 @@
 #include <asm/atomic.h>
 #include <asm/kvm.h>
 
+#include <sys/eventfd.h>
 #include <sys/ioctl.h>
 
 #include "kvm_util_arch.h"
@@ -502,6 +503,45 @@ static inline int vm_get_stats_fd(struct kvm_vm *vm)
 	return fd;
 }
 
+static inline int __kvm_irqfd(struct kvm_vm *vm, uint32_t gsi, int eventfd,
+			      uint32_t flags)
+{
+	struct kvm_irqfd irqfd = {
+		.fd = eventfd,
+		.gsi = gsi,
+		.flags = flags,
+		.resamplefd = -1,
+	};
+
+	return __vm_ioctl(vm, KVM_IRQFD, &irqfd);
+}
+
+static inline void kvm_irqfd(struct kvm_vm *vm, uint32_t gsi, int eventfd,
+			      uint32_t flags)
+{
+	int ret = __kvm_irqfd(vm, gsi, eventfd, flags);
+
+	TEST_ASSERT_VM_VCPU_IOCTL(!ret, KVM_IRQFD, ret, vm);
+}
+
+static inline void kvm_assign_irqfd(struct kvm_vm *vm, uint32_t gsi, int eventfd)
+{
+	kvm_irqfd(vm, gsi, eventfd, 0);
+}
+
+static inline void kvm_deassign_irqfd(struct kvm_vm *vm, uint32_t gsi, int eventfd)
+{
+	kvm_irqfd(vm, gsi, eventfd, KVM_IRQFD_FLAG_DEASSIGN);
+}
+
+static inline int kvm_new_eventfd(void)
+{
+	int fd = eventfd(0, 0);
+
+	TEST_ASSERT(fd >= 0, __KVM_SYSCALL_ERROR("eventfd()", fd));
+	return fd;
+}
+
 static inline void read_stats_header(int stats_fd, struct kvm_stats_header *header)
 {
 	ssize_t ret;

tools/testing/selftests/kvm/x86/xen_shinfo_test.c

@@ -547,11 +547,8 @@ int main(int argc, char *argv[])
 	int irq_fd[2] = { -1, -1 };
 
 	if (do_eventfd_tests) {
-		irq_fd[0] = eventfd(0, 0);
-		TEST_ASSERT(irq_fd[0] >= 0, __KVM_SYSCALL_ERROR("eventfd()", irq_fd[0]));
-
-		irq_fd[1] = eventfd(0, 0);
-		TEST_ASSERT(irq_fd[1] >= 0, __KVM_SYSCALL_ERROR("eventfd()", irq_fd[1]));
+		irq_fd[0] = kvm_new_eventfd();
+		irq_fd[1] = kvm_new_eventfd();
 
 		irq_routes.info.nr = 2;
 
@@ -569,15 +566,8 @@ int main(int argc, char *argv[])
 
 		vm_ioctl(vm, KVM_SET_GSI_ROUTING, &irq_routes.info);
 
-		struct kvm_irqfd ifd = { };
-
-		ifd.fd = irq_fd[0];
-		ifd.gsi = 32;
-		vm_ioctl(vm, KVM_IRQFD, &ifd);
-
-		ifd.fd = irq_fd[1];
-		ifd.gsi = 33;
-		vm_ioctl(vm, KVM_IRQFD, &ifd);
+		kvm_assign_irqfd(vm, 32, irq_fd[0]);
+		kvm_assign_irqfd(vm, 33, irq_fd[1]);
 
 		struct sigaction sa = { };
 		sa.sa_handler = handle_alrm;