linux/virt/kvm
Michael S. Tsirkin 68c3b4d167 KVM: VMX: speed up wildcard MMIO EVENTFD
With KVM, MMIO is much slower than PIO, due to the need to
do page walk and emulation. But with EPT, it does not have to be: we
know the address from the VMCS so if the address is unique, we can look
up the eventfd directly, bypassing emulation.

Unfortunately, this only works if userspace does not need to match on
access length and data.  The implementation adds a separate FAST_MMIO
bus internally. This serves two purposes:
    - minimize overhead for old userspace that does not use eventfd with lengtth = 0
    - minimize disruption in other code (since we don't know the length,
      devices on the MMIO bus only get a valid address in write, this
      way we don't need to touch all devices to teach them to handle
      an invalid length)

At the moment, this optimization only has effect for EPT on x86.

It will be possible to speed up MMIO for NPT and MMU using the same
idea in the future.

With this patch applied, on VMX MMIO EVENTFD is essentially as fast as PIO.
I was unable to detect any measureable slowdown to non-eventfd MMIO.

Making MMIO faster is important for the upcoming virtio 1.0 which
includes an MMIO signalling capability.

The idea was suggested by Peter Anvin.  Lots of thanks to Gleb for
pre-review and suggestions.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
2014-04-17 14:01:43 -03:00
..
arm arm, kvm: fix double lock on cpu_add_remove_lock 2014-04-08 13:15:54 +02:00
assigned-dev.c KVM: Move irq routing to generic code 2013-04-26 20:27:17 +02:00
async_pf.c KVM: async_pf: Add missing call for async page present 2014-02-04 04:24:05 +01:00
async_pf.h KVM: Halt vcpu if page it tries to access is swapped out 2011-01-12 11:21:39 +02:00
coalesced_mmio.c KVM: return an error code in kvm_vm_ioctl_register_coalesced_mmio() 2014-01-30 11:56:09 +01:00
coalesced_mmio.h KVM: Make coalesced mmio use a device per zone 2011-09-25 19:17:57 +03:00
eventfd.c KVM: VMX: speed up wildcard MMIO EVENTFD 2014-04-17 14:01:43 -03:00
ioapic.c KVM: ioapic: try to recover if pending_eoi goes out of range 2014-04-04 17:17:24 +02:00
ioapic.h kvm: make local functions static 2014-01-08 19:02:58 -02:00
iodev.h KVM: remove in_range from io devices 2009-09-10 08:33:05 +03:00
iommu.c KVM: IOMMU: hva align mapping page size 2013-11-05 09:55:36 +02:00
irq_comm.c KVM: Fix RTC interrupt coalescing tracking 2013-06-27 14:20:53 +03:00
irqchip.c KVM: Move irq routing setup to irqchip.c 2013-04-26 20:27:18 +02:00
Kconfig KVM: async_pf: Provide additional direct page notification 2014-01-30 12:51:38 +01:00
kvm_main.c KVM: VMX: speed up wildcard MMIO EVENTFD 2014-04-17 14:01:43 -03:00
vfio.c kvm/vfio: Support for DMA coherent IOMMUs 2014-02-26 11:38:40 -07:00