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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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3
include/uapi/linux/kvm.h
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@@ -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