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=-7.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS 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 B6B28C28CC3 for ; Fri, 7 Jun 2019 07:03:19 +0000 (UTC) Received: from mm01.cs.columbia.edu (mm01.cs.columbia.edu [128.59.11.253]) by mail.kernel.org (Postfix) with ESMTP id 46C3E208C3 for ; Fri, 7 Jun 2019 07:03:19 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 46C3E208C3 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com 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 A7AE04A4E1; Fri, 7 Jun 2019 03:03:18 -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 x4v+PQWfah0x; Fri, 7 Jun 2019 03:03:15 -0400 (EDT) Received: from mm01.cs.columbia.edu (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id CB6444A4BE; Fri, 7 Jun 2019 03:03:15 -0400 (EDT) Received: from localhost (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id 3EB7A4A4BE for ; Fri, 7 Jun 2019 03:03:14 -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 MlMCgfDLB0dr for ; Fri, 7 Jun 2019 03:03:11 -0400 (EDT) Received: from mx1.redhat.com (mx1.redhat.com [209.132.183.28]) by mm01.cs.columbia.edu (Postfix) with ESMTPS id 290074A380 for ; Fri, 7 Jun 2019 03:03:11 -0400 (EDT) Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 1DFC6C1EB214; Fri, 7 Jun 2019 07:02:52 +0000 (UTC) Received: from [10.36.116.67] (ovpn-116-67.ams2.redhat.com [10.36.116.67]) by smtp.corp.redhat.com (Postfix) with ESMTPS id ECBA9783A4; Fri, 7 Jun 2019 07:02:41 +0000 (UTC) Subject: Re: [PATCH v8 26/29] vfio-pci: Register an iommu fault handler To: Jacob Pan , Jean-Philippe Brucker References: <20190526161004.25232-1-eric.auger@redhat.com> <20190526161004.25232-27-eric.auger@redhat.com> <20190603163139.70fe8839@x1.home> <10dd60d9-4af0-c0eb-08c9-a0db7ee1925e@redhat.com> <20190605154553.0d00ad8d@jacob-builder> <2753d192-1c46-d78e-c425-0c828e48cde2@arm.com> <20190606132903.064f7ac4@jacob-builder> From: Auger Eric Message-ID: <10905d2d-16a5-7d6f-2db3-9cca10c3bde0@redhat.com> Date: Fri, 7 Jun 2019 09:02:35 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.4.0 MIME-Version: 1.0 In-Reply-To: <20190606132903.064f7ac4@jacob-builder> Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.32]); Fri, 07 Jun 2019 07:03:06 +0000 (UTC) Cc: "kevin.tian@intel.com" , "yi.l.liu@intel.com" , "ashok.raj@intel.com" , "kvm@vger.kernel.org" , Marc Zyngier , "joro@8bytes.org" , Will Deacon , "linux-kernel@vger.kernel.org" , "iommu@lists.linux-foundation.org" , Alex Williamson , Vincent Stehle , Robin Murphy , "kvmarm@lists.cs.columbia.edu" , "eric.auger.pro@gmail.com" 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 Jean, Jacob, On 6/6/19 10:29 PM, Jacob Pan wrote: > On Thu, 6 Jun 2019 19:54:05 +0100 > Jean-Philippe Brucker wrote: > >> On 05/06/2019 23:45, Jacob Pan wrote: >>> On Tue, 4 Jun 2019 18:11:08 +0200 >>> Auger Eric wrote: >>> >>>> Hi Alex, >>>> >>>> On 6/4/19 12:31 AM, Alex Williamson wrote: >>>>> On Sun, 26 May 2019 18:10:01 +0200 >>>>> Eric Auger wrote: >>>>> >>>>>> This patch registers a fault handler which records faults in >>>>>> a circular buffer and then signals an eventfd. This buffer is >>>>>> exposed within the fault region. >>>>>> >>>>>> Signed-off-by: Eric Auger >>>>>> >>>>>> --- >>>>>> >>>>>> v3 -> v4: >>>>>> - move iommu_unregister_device_fault_handler to vfio_pci_release >>>>>> --- >>>>>> drivers/vfio/pci/vfio_pci.c | 49 >>>>>> +++++++++++++++++++++++++++++ drivers/vfio/pci/vfio_pci_private.h >>>>>> | 1 + 2 files changed, 50 insertions(+) >>>>>> >>>>>> diff --git a/drivers/vfio/pci/vfio_pci.c >>>>>> b/drivers/vfio/pci/vfio_pci.c index f75f61127277..520999994ba8 >>>>>> 100644 --- a/drivers/vfio/pci/vfio_pci.c >>>>>> +++ b/drivers/vfio/pci/vfio_pci.c >>>>>> @@ -30,6 +30,7 @@ >>>>>> #include >>>>>> #include >>>>>> #include >>>>>> +#include >>>>>> >>>>>> #include "vfio_pci_private.h" >>>>>> >>>>>> @@ -296,6 +297,46 @@ static const struct vfio_pci_regops >>>>>> vfio_pci_fault_prod_regops = { .add_capability = >>>>>> vfio_pci_fault_prod_add_capability, }; >>>>>> >>>>>> +int vfio_pci_iommu_dev_fault_handler(struct iommu_fault_event >>>>>> *evt, void *data) +{ >>>>>> + struct vfio_pci_device *vdev = (struct vfio_pci_device >>>>>> *) data; >>>>>> + struct vfio_region_fault_prod *prod_region = >>>>>> + (struct vfio_region_fault_prod >>>>>> *)vdev->fault_pages; >>>>>> + struct vfio_region_fault_cons *cons_region = >>>>>> + (struct vfio_region_fault_cons >>>>>> *)(vdev->fault_pages + 2 * PAGE_SIZE); >>>>>> + struct iommu_fault *new = >>>>>> + (struct iommu_fault *)(vdev->fault_pages + >>>>>> prod_region->offset + >>>>>> + prod_region->prod * >>>>>> prod_region->entry_size); >>>>>> + int prod, cons, size; >>>>>> + >>>>>> + mutex_lock(&vdev->fault_queue_lock); >>>>>> + >>>>>> + if (!vdev->fault_abi) >>>>>> + goto unlock; >>>>>> + >>>>>> + prod = prod_region->prod; >>>>>> + cons = cons_region->cons; >>>>>> + size = prod_region->nb_entries; >>>>>> + >>>>>> + if (CIRC_SPACE(prod, cons, size) < 1) >>>>>> + goto unlock; >>>>>> + >>>>>> + *new = evt->fault; >>>>>> + prod = (prod + 1) % size; >>>>>> + prod_region->prod = prod; >>>>>> + mutex_unlock(&vdev->fault_queue_lock); >>>>>> + >>>>>> + mutex_lock(&vdev->igate); >>>>>> + if (vdev->dma_fault_trigger) >>>>>> + eventfd_signal(vdev->dma_fault_trigger, 1); >>>>>> + mutex_unlock(&vdev->igate); >>>>>> + return 0; >>>>>> + >>>>>> +unlock: >>>>>> + mutex_unlock(&vdev->fault_queue_lock); >>>>>> + return -EINVAL; >>>>>> +} >>>>>> + >>>>>> static int vfio_pci_init_fault_region(struct vfio_pci_device >>>>>> *vdev) { >>>>>> struct vfio_region_fault_prod *header; >>>>>> @@ -328,6 +369,13 @@ static int vfio_pci_init_fault_region(struct >>>>>> vfio_pci_device *vdev) header = (struct vfio_region_fault_prod >>>>>> *)vdev->fault_pages; header->version = -1; >>>>>> header->offset = PAGE_SIZE; >>>>>> + >>>>>> + ret = >>>>>> iommu_register_device_fault_handler(&vdev->pdev->dev, >>>>>> + >>>>>> vfio_pci_iommu_dev_fault_handler, >>>>>> + vdev); >>>>>> + if (ret) >>>>>> + goto out; >>>>>> + >>>>>> return 0; >>>>>> out: >>>>>> kfree(vdev->fault_pages); >>>>>> @@ -570,6 +618,7 @@ static void vfio_pci_release(void >>>>>> *device_data) if (!(--vdev->refcnt)) { >>>>>> vfio_spapr_pci_eeh_release(vdev->pdev); >>>>>> vfio_pci_disable(vdev); >>>>>> + >>>>>> iommu_unregister_device_fault_handler(&vdev->pdev->dev); >>>>> >>>>> >>>>> But this can fail if there are pending faults which leaves a >>>>> device reference and then the system is broken :( >>>> This series only features unrecoverable errors and for those the >>>> unregistration cannot fail. Now unrecoverable errors were added I >>>> admit this is confusing. We need to sort this out or clean the >>>> dependencies. >>> As Alex pointed out in 4/29, we can make >>> iommu_unregister_device_fault_handler() never fail and clean up all >>> the pending faults in the host IOMMU belong to that device. But the >>> problem is that if a fault, such as PRQ, has already been injected >>> into the guest, the page response may come back after handler is >>> unregistered and registered again. >> >> I'm trying to figure out if that would be harmful in any way. I guess >> it can be a bit nasty if we handle the page response right after >> having injected a new page request that uses the same PRGI. In any >> other case we discard the page response, but here we forward it to >> the endpoint and: >> >> * If the response status is success, endpoint retries the >> translation. The guest probably hasn't had time to handle the new >> page request and translation will fail, which may lead the endpoint >> to give up (two unsuccessful translation requests). Or send a new >> request >> > Good point, there shouldn't be any harm if the page response is a > "fake" success. In fact it could happen in the normal operation when > PRQs to two devices share the same non-leaf translation structure. The > worst case is just a retry. I am not aware of the retry limit, is it in > the PCIe spec? I cannot find it. > > I think we should just document it, similar to having a spurious > interrupt. The PRQ trace event should capture that as well. > >> * otherwise the endpoint won't retry the access, and could also >> disable PRI if the status is failure. >> > That would be true regardless this race condition with handler > registration. So should be fine. > >>> We need a way to reject such page response belong >>> to the previous life of the handler. Perhaps a sync call to the >>> guest with your fault queue eventfd? I am not sure. >> >> We could simply expect the device driver not to send any page response >> after unregistering the fault handler. Is there any reason VFIO would >> need to unregister and re-register the fault handler on a live guest? >> > There is no reason for VFIO to unregister and register again, I was > just thinking from security perspective. Someone could write a VFIO app > do this attack. But I agree the damage is within the device, may get > PRI disabled as a result. At the moment the handler unregistration is done on the vfio-pci release function() when the last reference is released so I am not sure this can even be achieved. > > So it seems we agree on the following: > - iommu_unregister_device_fault_handler() will never fail > - iommu driver cleans up all pending faults when handler is unregistered > - assume device driver or guest not sending more page response _after_ > handler is unregistered. > - system will tolerate rare spurious response > > Sounds right? sounds good for me Thanks Eric > >> Thanks, >> Jean > > [Jacob Pan] > _______________________________________________ kvmarm mailing list kvmarm@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/kvmarm