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=-8.5 required=3.0 tests=INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 autolearn=unavailable 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 07F52C3A59D for ; Thu, 22 Aug 2019 08:30:52 +0000 (UTC) Received: from mm01.cs.columbia.edu (mm01.cs.columbia.edu [128.59.11.253]) by mail.kernel.org (Postfix) with ESMTP id 838932342F for ; Thu, 22 Aug 2019 08:30:51 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 838932342F Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kvmarm-bounces@lists.cs.columbia.edu Received: from localhost (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id E72784A5A9; Thu, 22 Aug 2019 04:30:50 -0400 (EDT) X-Virus-Scanned: at lists.cs.columbia.edu Received: from mm01.cs.columbia.edu ([127.0.0.1]) by localhost (mm01.cs.columbia.edu [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id 1DZkNPTG0Jr0; Thu, 22 Aug 2019 04:30:49 -0400 (EDT) Received: from mm01.cs.columbia.edu (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id C6BEA4A581; Thu, 22 Aug 2019 04:30:49 -0400 (EDT) Received: from localhost (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id 76CD34A57F for ; Thu, 22 Aug 2019 04:30:48 -0400 (EDT) X-Virus-Scanned: at lists.cs.columbia.edu Received: from mm01.cs.columbia.edu ([127.0.0.1]) by localhost (mm01.cs.columbia.edu [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id XStMxUVzIK4U for ; Thu, 22 Aug 2019 04:30:47 -0400 (EDT) Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by mm01.cs.columbia.edu (Postfix) with ESMTP id 3EF7F4A55D for ; Thu, 22 Aug 2019 04:30:47 -0400 (EDT) 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 A3E0D344; Thu, 22 Aug 2019 01:30:46 -0700 (PDT) Received: from [10.1.197.61] (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id E11A33F706; Thu, 22 Aug 2019 01:30:45 -0700 (PDT) Subject: Re: [PATCH] arm64: KVM: Only skip MMIO insn once To: Andrew Jones , kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org References: <20190821195030.2569-1-drjones@redhat.com> From: Marc Zyngier Organization: Approximate Message-ID: <177091d5-2d2c-6a75-472c-92702ee98e86@kernel.org> Date: Thu, 22 Aug 2019 09:30:44 +0100 User-Agent: Mozilla/5.0 (X11; Linux aarch64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <20190821195030.2569-1-drjones@redhat.com> Content-Language: en-US X-BeenThere: kvmarm@lists.cs.columbia.edu X-Mailman-Version: 2.1.14 Precedence: list List-Id: Where KVM/ARM decisions are made List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: kvmarm-bounces@lists.cs.columbia.edu Sender: kvmarm-bounces@lists.cs.columbia.edu Hi Drew, On 21/08/2019 20:50, 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 > --- > virt/kvm/arm/arm.c | 3 ++- > virt/kvm/arm/mmio.c | 1 + > 2 files changed, 3 insertions(+), 1 deletion(-) > > diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c > index 35a069815baf..322cf9030bbe 100644 > --- a/virt/kvm/arm/arm.c > +++ b/virt/kvm/arm/arm.c > @@ -669,7 +669,8 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *run) > if (ret) > return ret; > > - if (run->exit_reason == KVM_EXIT_MMIO) { > + if (vcpu->mmio_needed) { > + vcpu->mmio_needed = 0; > ret = kvm_handle_mmio_return(vcpu, vcpu->run); > if (ret) > return ret; > diff --git a/virt/kvm/arm/mmio.c b/virt/kvm/arm/mmio.c > index a8a6a0c883f1..2d9b5e064ae0 100644 > --- a/virt/kvm/arm/mmio.c > +++ b/virt/kvm/arm/mmio.c > @@ -201,6 +201,7 @@ int io_mem_abort(struct kvm_vcpu *vcpu, struct kvm_run *run, > if (is_write) > memcpy(run->mmio.data, data_buf, len); > vcpu->stat.mmio_exit_user++; > + vcpu->mmio_needed = 1; > run->exit_reason = KVM_EXIT_MMIO; > return 0; > } > Thanks for this. That's quite embarrassing. Out of curiosity, how was this spotted? Patch wise, I'd have a small preference for the following (untested) patch, as it keeps the mmio_needed accesses close together, making it easier to read (at least for me). What do you think? M. 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. */ -- Jazz is not dead, it just smells funny... _______________________________________________ kvmarm mailing list kvmarm@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/kvmarm