From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0a-001b2d01.pphosted.com (mx0b-001b2d01.pphosted.com [148.163.158.5]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 41d07V1LzJzF0dl for ; Sat, 28 Jul 2018 18:56:37 +1000 (AEST) Received: from pps.filterd (m0098421.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.22/8.16.0.22) with SMTP id w6S8rupX028965 for ; Sat, 28 Jul 2018 04:56:35 -0400 Received: from e06smtp05.uk.ibm.com (e06smtp05.uk.ibm.com [195.75.94.101]) by mx0a-001b2d01.pphosted.com with ESMTP id 2kgmg31eru-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Sat, 28 Jul 2018 04:56:35 -0400 Received: from localhost by e06smtp05.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Sat, 28 Jul 2018 09:56:33 +0100 Subject: Re: [RFC 2/4] virtio: Override device's DMA OPS with virtio_direct_dma_ops selectively To: virtualization@lists.linux-foundation.org, linux-kernel@vger.kernel.org References: <20180720035941.6844-1-khandual@linux.vnet.ibm.com> <20180720035941.6844-3-khandual@linux.vnet.ibm.com> Cc: linuxppc-dev@lists.ozlabs.org, aik@ozlabs.ru, robh@kernel.org, joe@perches.com, elfring@users.sourceforge.net, david@gibson.dropbear.id.au, jasowang@redhat.com, benh@kernel.crashing.org, mpe@ellerman.id.au, mst@redhat.com, hch@infradead.org, linuxram@us.ibm.com, haren@linux.vnet.ibm.com, paulus@samba.org, srikar@linux.vnet.ibm.com From: Anshuman Khandual Date: Sat, 28 Jul 2018 14:26:24 +0530 MIME-Version: 1.0 In-Reply-To: <20180720035941.6844-3-khandual@linux.vnet.ibm.com> Content-Type: text/plain; charset=windows-1252 Message-Id: List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On 07/20/2018 09:29 AM, Anshuman Khandual wrote: > Now that virtio core always needs all virtio devices to have DMA OPS, we > need to make sure that the structure it points is the right one. In the > absence of VIRTIO_F_IOMMU_PLATFORM flag QEMU expects GPA from guest kernel. > In such case, virtio device must use default virtio_direct_dma_ops DMA OPS > structure which transforms scatter gather buffer addresses as GPA. This > DMA OPS override must happen as early as possible during virtio device > initializatin sequence before virtio core starts using given device's DMA > OPS callbacks for I/O transactions. This change detects device's IOMMU flag > and does the override in case the flag is cleared. > > Signed-off-by: Anshuman Khandual > --- > drivers/virtio/virtio.c | 5 +++++ > 1 file changed, 5 insertions(+) > > diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c > index 7907ad3..6b13987 100644 > --- a/drivers/virtio/virtio.c > +++ b/drivers/virtio/virtio.c > @@ -166,6 +166,8 @@ void virtio_add_status(struct virtio_device *dev, unsigned int status) > } > EXPORT_SYMBOL_GPL(virtio_add_status); > > +const struct dma_map_ops virtio_direct_dma_ops; > + > int virtio_finalize_features(struct virtio_device *dev) > { > int ret = dev->config->finalize_features(dev); > @@ -174,6 +176,9 @@ int virtio_finalize_features(struct virtio_device *dev) > if (ret) > return ret; The previous patch removed the code block for XEN guests which forced the use of DMA API all the time irrespective of VIRTIO_F_IOMMU_PLATFORM flag on the device. Here is what I have removed with patch 2/4 which breaks the existing semantics on XEN guests. -static bool vring_use_dma_api(struct virtio_device *vdev) -{ - if (!virtio_has_iommu_quirk(vdev)) - return true; - - /* Otherwise, we are left to guess. */ - /* - * In theory, it's possible to have a buggy QEMU-supposed - * emulated Q35 IOMMU and Xen enabled at the same time. On - * such a configuration, virtio has never worked and will - * not work without an even larger kludge. Instead, enable - * the DMA API if we're a Xen guest, which at least allows - * all of the sensible Xen configurations to work correctly. - */ - if (xen_domain()) - return true; - - return false; -} XEN guests would not like override with virtio_direct_dma_ops in any case irrespective of the flag VIRTIO_F_IOMMU_PLATFORM. So the existing semantics can be preserved with something like this. It just assumes that dev->dma_ops is non-NULL and a valid one set by the architecture. If required we can add those tests here before skipping the override. diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c index 7907ad3..6b13987 100644 --- a/drivers/virtio/virtio.c +++ b/drivers/virtio/virtio.c @@ -166,6 +166,8 @@ void virtio_add_status(struct virtio_device *dev, unsigned int status) } EXPORT_SYMBOL_GPL(virtio_add_status); +const struct dma_map_ops virtio_direct_dma_ops; + int virtio_finalize_features(struct virtio_device *dev) { int ret = dev->config->finalize_features(dev); @@ -174,6 +176,9 @@ int virtio_finalize_features(struct virtio_device *dev) if (ret) return ret; + + if (xen_domain()) + goto skip_override; + + if (virtio_has_iommu_quirk(dev)) + set_dma_ops(dev->dev.parent, &virtio_direct_dma_ops); + + skip_override: + if (!virtio_has_feature(dev, VIRTIO_F_VERSION_1)) return 0 Will incorporate these changes in the next version.