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Diffstat (limited to 'Documentation/virtual')
| -rw-r--r-- | Documentation/virtual/kvm/api.txt | 24 |
1 files changed, 24 insertions, 0 deletions
diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt index 48e5d1197295..10d48eb67da9 100644 --- a/Documentation/virtual/kvm/api.txt +++ b/Documentation/virtual/kvm/api.txt @@ -3681,6 +3681,30 @@ Returns: 0 on success, -1 on error This copies the vcpu's kvm_nested_state struct from userspace to the kernel. For the definition of struct kvm_nested_state, see KVM_GET_NESTED_STATE. +4.116 KVM_(UN)REGISTER_COALESCED_MMIO + +Capability: KVM_CAP_COALESCED_MMIO +Architectures: all +Type: vm ioctl +Parameters: struct kvm_coalesced_mmio_zone +Returns: 0 on success, < 0 on error + +Coalesced mmio is a performance optimization that defers hardware +register write emulation so that userspace exits are avoided. It is +typically used to reduce the overhead of emulating frequently accessed +hardware registers. + +When a hardware register is configured for coalesced mmio, write accesses +do not exit to userspace and their value is recorded in a ring buffer +that is shared between kernel and userspace. + +Coalesced mmio is used if one or more write accesses to a hardware +register can be deferred until a read or a write to another hardware +register on the same device. This last access will cause a vmexit and +userspace will process accesses from the ring buffer before emulating +it. That will avoid exiting to userspace on repeated writes to the +first register. + 5. The kvm_run structure ------------------------ |