Commit f848a5a8 authored by Michael S. Tsirkin's avatar Michael S. Tsirkin Committed by Marcelo Tosatti
Browse files

KVM: support any-length wildcard ioeventfd 



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: default avatarMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: default avatarMarcelo Tosatti <mtosatti@redhat.com>
parent cd9ae5fe

arch/x86/kvm/x86.c

+1 −0
Original line number Diff line number Diff line
@@ -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:

include/uapi/linux/kvm.h

+2 −1
Original line number Diff line number Diff line
@@ -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

virt/kvm/eventfd.c

+22 −5
Original line number Diff line number Diff line
@@ -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->addr == p->addr &&

		    (!_p->length || !p->length ||

		     (_p->length == p->length &&

		      (_p->wildcard || p->wildcard ||

		     _p->datamatch == p->datamatch))

		       _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);

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