kvm: add capability for any-length ioeventfds
Cc: Gleb Natapov <gleb@kernel.org>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
index e3e9c41..34cc068 100644
--- a/Documentation/virtual/kvm/api.txt
+++ b/Documentation/virtual/kvm/api.txt
@@ -1604,7 +1604,7 @@
struct kvm_ioeventfd {
__u64 datamatch;
__u64 addr; /* legal pio/mmio address */
- __u32 len; /* 1, 2, 4, or 8 bytes */
+ __u32 len; /* 0, 1, 2, 4, or 8 bytes */
__s32 fd;
__u32 flags;
__u8 pad[36];
@@ -1627,6 +1627,10 @@
For virtio-ccw devices, addr contains the subchannel id and datamatch the
virtqueue index.
+With KVM_CAP_IOEVENTFD_ANY_LENGTH, a zero length ioeventfd is allowed, and
+the kernel will ignore the length of guest write and may get a faster vmexit.
+The speedup may only apply to specific architectures, but the ioeventfd will
+work anyway.
4.60 KVM_DIRTY_TLB
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index 12e3afb..03f3618 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -830,6 +830,7 @@
#define KVM_CAP_GUEST_DEBUG_HW_BPS 119
#define KVM_CAP_GUEST_DEBUG_HW_WPS 120
#define KVM_CAP_SPLIT_IRQCHIP 121
+#define KVM_CAP_IOEVENTFD_ANY_LENGTH 122
#ifdef KVM_CAP_IRQ_ROUTING
diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c
index 79db453..ac89299 100644
--- a/virt/kvm/eventfd.c
+++ b/virt/kvm/eventfd.c
@@ -914,9 +914,7 @@
return -EINVAL;
/* ioeventfd with no length can't be combined with DATAMATCH */
- if (!args->len &&
- args->flags & (KVM_IOEVENTFD_FLAG_PIO |
- KVM_IOEVENTFD_FLAG_DATAMATCH))
+ if (!args->len && (args->flags & KVM_IOEVENTFD_FLAG_DATAMATCH))
return -EINVAL;
ret = kvm_assign_ioeventfd_idx(kvm, bus_idx, args);
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 23116dc..afd7ae6 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -2718,6 +2718,7 @@
case KVM_CAP_IRQFD:
case KVM_CAP_IRQFD_RESAMPLE:
#endif
+ case KVM_CAP_IOEVENTFD_ANY_LENGTH:
case KVM_CAP_CHECK_EXTENSION_VM:
return 1;
#ifdef CONFIG_HAVE_KVM_IRQ_ROUTING
