It is sometimes benefitial to ignore IO size, and only match on address.
In hindsight this would have been a better default than matching length
when KVM_IOEVENTFD_FLAG_DATAMATCH is not set, In particular, this kind
of access can be optimized on VMX: there no need to do page lookups.
This can currently be done with many ioeventfds but in a suboptimal way.
However we can't change kernel/userspace ABI without risk of breaking
some applications.
Use len = 0 to mean "ignore length for matching" in a more optimal way.
Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
---
include/uapi/linux/kvm.h | 3 ++-
arch/x86/kvm/x86.c | 1 +
virt/kvm/eventfd.c | 27 ++++++++++++++++++++++-----
3 files changed, 25 insertions(+), 6 deletions(-)
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index 932d7f2..d73007e 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -464,7 +464,7 @@ enum {
struct kvm_ioeventfd {
__u64 datamatch;
__u64 addr; /* legal pio/mmio address */
- __u32 len; /* 1, 2, 4, or 8 bytes */
+ __u32 len; /* 1, 2, 4, or 8 bytes; or 0 to ignore length */
__s32 fd;
__u32 flags;
__u8 pad[36];
@@ -675,6 +675,7 @@ struct kvm_ppc_smmu_info {
#define KVM_CAP_SPAPR_MULTITCE 94
#define KVM_CAP_EXT_EMUL_CPUID 95
#define KVM_CAP_HYPERV_TIME 96
+#define KVM_CAP_IOEVENTFD_NO_LENGTH 97
#ifdef KVM_CAP_IRQ_ROUTING
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 0c6218b..8ae1ff5 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2602,6 +2602,7 @@ int kvm_dev_ioctl_check_extension(long ext)
case KVM_CAP_IRQ_INJECT_STATUS:
case KVM_CAP_IRQFD:
case KVM_CAP_IOEVENTFD:
+ case KVM_CAP_IOEVENTFD_NO_LENGTH:
case KVM_CAP_PIT2:
case KVM_CAP_PIT_STATE2:
case KVM_CAP_SET_IDENTITY_MAP_ADDR:
diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c
index abe4d60..9eadb59 100644
--- a/virt/kvm/eventfd.c
+++ b/virt/kvm/eventfd.c
@@ -600,7 +600,15 @@ ioeventfd_in_range(struct _ioeventfd *p, gpa_t addr, int len, const void *val)
{
u64 _val;
- if (!(addr == p->addr && len == p->length))
+ if (addr != p->addr)
+ /* address must be precise for a hit */
+ return false;
+
+ if (!p->length)
+ /* length = 0 means only look at the address, so always a hit */
+ return true;
+
+ if (len != p->length)
/* address-range must be precise for a hit */
return false;
@@ -671,9 +679,11 @@ ioeventfd_check_collision(struct kvm *kvm, struct _ioeventfd *p)
list_for_each_entry(_p, &kvm->ioeventfds, list)
if (_p->bus_idx == p->bus_idx &&
- _p->addr == p->addr && _p->length == p->length &&
- (_p->wildcard || p->wildcard ||
- _p->datamatch == p->datamatch))
+ _p->addr == p->addr &&
+ (!_p->length || !p->length ||
+ (_p->length == p->length &&
+ (_p->wildcard || p->wildcard ||
+ _p->datamatch == p->datamatch))))
return true;
return false;
@@ -697,8 +707,9 @@ kvm_assign_ioeventfd(struct kvm *kvm, struct kvm_ioeventfd *args)
int ret;
bus_idx = ioeventfd_bus_from_flags(args->flags);
- /* must be natural-word sized */
+ /* must be natural-word sized, or 0 to ignore length */
switch (args->len) {
+ case 0:
case 1:
case 2:
case 4:
@@ -716,6 +727,12 @@ kvm_assign_ioeventfd(struct kvm *kvm, struct kvm_ioeventfd *args)
if (args->flags & ~KVM_IOEVENTFD_VALID_FLAG_MASK)
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))
+ return -EINVAL;
+
eventfd = eventfd_ctx_fdget(args->fd);
if (IS_ERR(eventfd))
return PTR_ERR(eventfd);
--
MST
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