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KVM: support any-length wildcard ioeventfd

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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@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
This commit is contained in:
Michael S. Tsirkin 2014-03-31 21:50:38 +03:00 committed by Marcelo Tosatti
parent cd9ae5fe47
commit f848a5a8dc
3 changed files with 25 additions and 6 deletions
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1
arch/x86/kvm/x86.c
View file

@ -2644,6 +2644,7 @@ 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:

3
include/uapi/linux/kvm.h
View file

@ -529,7 +529,7 @@ 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];
@ -743,6 +743,7 @@ struct kvm_ppc_smmu_info {
#define KVM_CAP_IOAPIC_POLARITY_IGNORED 97
#define KVM_CAP_ENABLE_CAP_VM 98
#define KVM_CAP_S390_IRQCHIP 99
#define KVM_CAP_IOEVENTFD_NO_LENGTH 100
#ifdef KVM_CAP_IRQ_ROUTING

27
virt/kvm/eventfd.c
View file

@ -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);