Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1215886

[PATCH RFC 2/3] svm: allow ioeventfd for NPT page faults

Show all headers | View raw

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.

Warning: untested.

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

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 8e0c084..6422fac 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -1812,6 +1812,11 @@ static int pf_interception(struct vcpu_svm *svm)
 	switch (svm->apf_reason) {
 	default:
 		error_code = svm->vmcb->control.exit_info_1;
+		if (!kvm_io_bus_write(&svm->vcpu, KVM_FAST_MMIO_BUS,
+				      fault_address, 0, NULL)) {
+			skip_emulated_instruction(&svm->vcpu);
+			return 1;
+		}
 
 		trace_kvm_page_fault(fault_address, error_code);
 		if (!npt_enabled && kvm_event_needs_reinjection(&svm->vcpu))
-- 
MST

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

Back to linux.kernel | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

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

csiph-web