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[PATCH RFC 1/3] vmx: allow ioeventfd for EPT violations

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Even when we skip data decoding, MMIO is slightly slower
than port IO because it uses the page-tables, so the CPU
must do a pagewalk on each access.

This overhead is normally masked by using the TLB cache:
but not so for KVM MMIO, where PTEs are marked as reserved
and so are never cached.

As ioeventfd memory is never read, make it possible to use
RO pages on the host for ioeventfds, instead.
The result is that TLBs are cached, which finally makes MMIO
as fast as port IO.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
 arch/x86/kvm/vmx.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 9d1bfd3..ed44026 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -5745,6 +5745,11 @@ static int handle_ept_violation(struct kvm_vcpu *vcpu)
 		vmcs_set_bits(GUEST_INTERRUPTIBILITY_INFO, GUEST_INTR_STATE_NMI);
 
 	gpa = vmcs_read64(GUEST_PHYSICAL_ADDRESS);
+	if (!kvm_io_bus_write(vcpu, KVM_FAST_MMIO_BUS, gpa, 0, NULL)) {
+		skip_emulated_instruction(vcpu);
+		return 1;
+	}
+
 	trace_kvm_page_fault(gpa, exit_qualification);
 
 	/* It is a write fault? */
-- 
MST

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Thread

[PATCH RFC 0/3] kvm add ioeventfd pf capability "Michael S. Tsirkin" <mst@redhat.com> - 2015-08-30 11:20 +0200
  [PATCH RFC 1/3] vmx: allow ioeventfd for EPT violations "Michael S. Tsirkin" <mst@redhat.com> - 2015-08-30 11:20 +0200
    Re: [PATCH RFC 1/3] vmx: allow ioeventfd for EPT violations Xiao Guangrong <guangrong.xiao@linux.intel.com> - 2015-08-31 05:10 +0200
      Re: [PATCH RFC 1/3] vmx: allow ioeventfd for EPT violations "Michael S. Tsirkin" <mst@redhat.com> - 2015-08-31 09:50 +0200
        Re: [PATCH RFC 1/3] vmx: allow ioeventfd for EPT violations Xiao Guangrong <guangrong.xiao@linux.intel.com> - 2015-08-31 10:40 +0200
          Re: [PATCH RFC 1/3] vmx: allow ioeventfd for EPT violations "Michael S. Tsirkin" <mst@redhat.com> - 2015-08-31 13:30 +0200
            Re: [PATCH RFC 1/3] vmx: allow ioeventfd for EPT violations Xiao Guangrong <guangrong.xiao@linux.intel.com> - 2015-08-31 15:30 +0200
              Re: [PATCH RFC 1/3] vmx: allow ioeventfd for EPT violations "Michael S. Tsirkin" <mst@redhat.com> - 2015-08-31 17:00 +0200
    Re: [PATCH RFC 1/3] vmx: allow ioeventfd for EPT violations Jason Wang <jasowang@redhat.com> - 2015-09-01 05:40 +0200
      Re: [PATCH RFC 1/3] vmx: allow ioeventfd for EPT violations "Michael S. Tsirkin" <mst@redhat.com> - 2015-09-01 06:40 +0200
        Re: [PATCH RFC 1/3] vmx: allow ioeventfd for EPT violations Jason Wang <jasowang@redhat.com> - 2015-09-01 06:50 +0200
          Re: [PATCH RFC 1/3] vmx: allow ioeventfd for EPT violations "Michael S. Tsirkin" <mst@redhat.com> - 2015-09-01 09:00 +0200
  [PATCH RFC 2/3] svm: allow ioeventfd for NPT page faults "Michael S. Tsirkin" <mst@redhat.com> - 2015-08-30 11:20 +0200
  [PATCH RFC 3/3] kvm: add KVM_CAP_IOEVENTFD_PF capability "Michael S. Tsirkin" <mst@redhat.com> - 2015-08-30 11:20 +0200

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