On 10/07/2024 10:52, Ilias Stamatis wrote:
The current MMIO coalescing design has a few drawbacks which limit its usefulness. Currently all coalesced MMIO zones use the same ring buffer. That means that upon a userspace exit we have to handle potentially unrelated MMIO writes synchronously. And a VM-wide lock needs to be taken in the kernel when an MMIO exit occurs. Additionally, there is no direct way for userspace to be notified about coalesced MMIO writes. If the next MMIO exit to userspace is when the ring buffer has filled then a substantial (and unbounded) amount of time may have passed since the first coalesced MMIO. Add a KVM_CREATE_COALESCED_MMIO_BUFFER ioctl to KVM. This ioctl simply returns a file descriptor to the caller but does not allocate a ring buffer. Userspace can then pass this fd to mmap() to actually allocate a buffer and map it to its address space. Subsequent patches will allow userspace to: - Associate the fd with a coalescing zone when registering it so that writes to that zone are accumulated in that specific ring buffer rather than the VM-wide one. - Poll for MMIO writes using this fd. Signed-off-by: Ilias Stamatis <ilstam@xxxxxxxxxx> --- include/linux/kvm_host.h | 1 + include/uapi/linux/kvm.h | 2 + virt/kvm/coalesced_mmio.c | 142 +++++++++++++++++++++++++++++++++++--- virt/kvm/coalesced_mmio.h | 9 +++ virt/kvm/kvm_main.c | 4 ++ 5 files changed, 150 insertions(+), 8 deletions(-)
Reviewed-by: Paul Durrant <paul@xxxxxxx>
