From: Jason Wang <jasowang@xxxxxxxxxx>
Cc: Gleb Natapov <gleb@xxxxxxxxxx>
Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
---
Documentation/virtual/kvm/api.txt | 6 +++++-
include/uapi/linux/kvm.h | 1 +
virt/kvm/eventfd.c | 4 +---
virt/kvm/kvm_main.c | 1 +
4 files changed, 8 insertions(+), 4 deletions(-)
diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
index e3e9c41721a2..34cc068e81ea 100644
--- a/Documentation/virtual/kvm/api.txt
+++ b/Documentation/virtual/kvm/api.txt
@@ -1604,7 +1604,7 @@ provided event instead of triggering an exit.
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 @@ to the registered address is equal to datamatch in struct kvm_ioeventfd.
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 12e3afbf0f47..03f3618612aa 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -830,6 +830,7 @@ struct kvm_ppc_smmu_info {
#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 79db45336e3a..ac89299b8699 100644
--- a/virt/kvm/eventfd.c
+++ b/virt/kvm/eventfd.c
@@ -914,9 +914,7 @@ kvm_assign_ioeventfd(struct kvm *kvm, struct kvm_ioeventfd *args)
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 23116dcb2129..afd7ae6aec65 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -2718,6 +2718,7 @@ static long kvm_vm_ioctl_check_extension_generic(struct kvm *kvm, long arg)
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
--
1.8.3.1
--
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