Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755264AbbIADhT (ORCPT ); Mon, 31 Aug 2015 23:37:19 -0400 Received: from mx1.redhat.com ([209.132.183.28]:41512 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751828AbbIADhR (ORCPT ); Mon, 31 Aug 2015 23:37:17 -0400 Message-ID: <55E51D69.2010303@redhat.com> Date: Tue, 01 Sep 2015 11:37:13 +0800 From: Jason Wang User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.8.0 MIME-Version: 1.0 To: "Michael S. Tsirkin" , linux-kernel@vger.kernel.org CC: kvm@vger.kernel.org, Paolo Bonzini Subject: Re: [PATCH RFC 1/3] vmx: allow ioeventfd for EPT violations References: <1440925898-23440-1-git-send-email-mst@redhat.com> <1440925898-23440-2-git-send-email-mst@redhat.com> In-Reply-To: <1440925898-23440-2-git-send-email-mst@redhat.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1652 Lines: 46 On 08/30/2015 05:12 PM, Michael S. Tsirkin wrote: > 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 > --- > 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? */ Just notice that vcpu_mmio_write() tries lapic first. Should we do the same here? Otherwise we may slow down apic access consider we may have hundreds of eventfds. -- 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/