From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id DBB23C3A5A1 for ; Thu, 22 Aug 2019 11:59:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B975A233FE for ; Thu, 22 Aug 2019 11:59:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1733306AbfHVL7d (ORCPT ); Thu, 22 Aug 2019 07:59:33 -0400 Received: from foss.arm.com ([217.140.110.172]:44784 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731156AbfHVL7d (ORCPT ); Thu, 22 Aug 2019 07:59:33 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 27330337; Thu, 22 Aug 2019 04:59:32 -0700 (PDT) Received: from lakrids.cambridge.arm.com (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 74E833F718; Thu, 22 Aug 2019 04:59:31 -0700 (PDT) Date: Thu, 22 Aug 2019 12:59:23 +0100 From: Mark Rutland To: Andrew Jones Cc: kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org, maz@kernel.org Subject: Re: [PATCH v2] arm64: KVM: Only skip MMIO insn once Message-ID: <20190822115923.GA33080@lakrids.cambridge.arm.com> References: <20190822110305.18035-1-drjones@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190822110305.18035-1-drjones@redhat.com> User-Agent: Mutt/1.11.1+11 (2f07cb52) (2018-12-01) Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Thu, Aug 22, 2019 at 01:03:05PM +0200, Andrew Jones wrote: > If after an MMIO exit to userspace a VCPU is immediately run with an > immediate_exit request, such as when a signal is delivered or an MMIO > emulation completion is needed, then the VCPU completes the MMIO > emulation and immediately returns to userspace. As the exit_reason > does not get changed from KVM_EXIT_MMIO in these cases we have to > be careful not to complete the MMIO emulation again, when the VCPU is > eventually run again, because the emulation does an instruction skip > (and doing too many skips would be a waste of guest code :-) We need > to use additional VCPU state to track if the emulation is complete. > As luck would have it, we already have 'mmio_needed', which even > appears to be used in this way by other architectures already. > > Fixes: 0d640732dbeb ("arm64: KVM: Skip MMIO insn after emulation") > Signed-off-by: Andrew Jones Ouch; sorry about this! I haven't dug too deeply, but from the commit message, the below makes sense to me. FWIW: Acked-by: Mark Rutland Mark. > --- > v2: move mmio_needed use closer to other mmio state use [maz] > > virt/kvm/arm/mmio.c | 7 +++++++ > 1 file changed, 7 insertions(+) > > diff --git a/virt/kvm/arm/mmio.c b/virt/kvm/arm/mmio.c > index a8a6a0c883f1..6af5c91337f2 100644 > --- a/virt/kvm/arm/mmio.c > +++ b/virt/kvm/arm/mmio.c > @@ -86,6 +86,12 @@ int kvm_handle_mmio_return(struct kvm_vcpu *vcpu, struct kvm_run *run) > unsigned int len; > int mask; > > + /* Detect an already handled MMIO return */ > + if (unlikely(!vcpu->mmio_needed)) > + return 0; > + > + vcpu->mmio_needed = 0; > + > if (!run->mmio.is_write) { > len = run->mmio.len; > if (len > sizeof(unsigned long)) > @@ -188,6 +194,7 @@ int io_mem_abort(struct kvm_vcpu *vcpu, struct kvm_run *run, > run->mmio.is_write = is_write; > run->mmio.phys_addr = fault_ipa; > run->mmio.len = len; > + vcpu->mmio_needed = 1; > > if (!ret) { > /* We handled the access successfully in the kernel. */ > -- > 2.18.1 >