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Violators will be prosecuted for from ; Wed, 25 Jul 2018 05:30:49 +0100 Subject: Re: [RFC 4/4] virtio: Add platform specific DMA API translation for virito devices To: "Michael S. Tsirkin" References: <20180720035941.6844-1-khandual@linux.vnet.ibm.com> <20180720035941.6844-5-khandual@linux.vnet.ibm.com> <20180720160550-mutt-send-email-mst@kernel.org> <3dd36d8e-3bc8-91ba-cf6d-939495439d2c@linux.vnet.ibm.com> Cc: robh@kernel.org, srikar@linux.vnet.ibm.com, aik@ozlabs.ru, jasowang@redhat.com, linuxram@us.ibm.com, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, hch@infradead.org, paulus@samba.org, joe@perches.com, linuxppc-dev@lists.ozlabs.org, elfring@users.sourceforge.net, haren@linux.vnet.ibm.com, david@gibson.dropbear.id.au From: Anshuman Khandual Date: Wed, 25 Jul 2018 10:00:39 +0530 MIME-Version: 1.0 In-Reply-To: <3dd36d8e-3bc8-91ba-cf6d-939495439d2c@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 07/23/2018 07:46 AM, Anshuman Khandual wrote: > On 07/20/2018 06:45 PM, Michael S. Tsirkin wrote: >> On Fri, Jul 20, 2018 at 09:29:41AM +0530, Anshuman Khandual wrote: >>> Subject: Re: [RFC 4/4] virtio: Add platform specific DMA API translation for >>> virito devices >> >> s/virito/virtio/ > > Oops, will fix it. Thanks for pointing out. > >> >>> This adds a hook which a platform can define in order to allow it to >>> override virtio device's DMA OPS irrespective of whether it has the >>> flag VIRTIO_F_IOMMU_PLATFORM set or not. We want to use this to do >>> bounce-buffering of data on the new secure pSeries platform, currently >>> under development, where a KVM host cannot access all of the memory >>> space of a secure KVM guest. The host can only access the pages which >>> the guest has explicitly requested to be shared with the host, thus >>> the virtio implementation in the guest has to copy data to and from >>> shared pages. >>> >>> With this hook, the platform code in the secure guest can force the >>> use of swiotlb for virtio buffers, with a back-end for swiotlb which >>> will use a pool of pre-allocated shared pages. Thus all data being >>> sent or received by virtio devices will be copied through pages which >>> the host has access to. >>> >>> Signed-off-by: Anshuman Khandual >>> --- >>> arch/powerpc/include/asm/dma-mapping.h | 6 ++++++ >>> arch/powerpc/platforms/pseries/iommu.c | 6 ++++++ >>> drivers/virtio/virtio.c | 7 +++++++ >>> 3 files changed, 19 insertions(+) >>> >>> diff --git a/arch/powerpc/include/asm/dma-mapping.h b/arch/powerpc/include/asm/dma-mapping.h >>> index 8fa3945..bc5a9d3 100644 >>> --- a/arch/powerpc/include/asm/dma-mapping.h >>> +++ b/arch/powerpc/include/asm/dma-mapping.h >>> @@ -116,3 +116,9 @@ extern u64 __dma_get_required_mask(struct device *dev); >>> >>> #endif /* __KERNEL__ */ >>> #endif /* _ASM_DMA_MAPPING_H */ >>> + >>> +#define platform_override_dma_ops platform_override_dma_ops >>> + >>> +struct virtio_device; >>> + >>> +extern void platform_override_dma_ops(struct virtio_device *vdev); >>> diff --git a/arch/powerpc/platforms/pseries/iommu.c b/arch/powerpc/platforms/pseries/iommu.c >>> index 06f0296..5773bc7 100644 >>> --- a/arch/powerpc/platforms/pseries/iommu.c >>> +++ b/arch/powerpc/platforms/pseries/iommu.c >>> @@ -38,6 +38,7 @@ >>> #include >>> #include >>> #include >>> +#include >>> #include >>> #include >>> #include >>> @@ -1396,3 +1397,8 @@ static int __init disable_multitce(char *str) >>> __setup("multitce=", disable_multitce); >>> >>> machine_subsys_initcall_sync(pseries, tce_iommu_bus_notifier_init); >>> + >>> +void platform_override_dma_ops(struct virtio_device *vdev) >>> +{ >>> + /* Override vdev->parent.dma_ops if required */ >>> +} >>> diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c >>> index 6b13987..432c332 100644 >>> --- a/drivers/virtio/virtio.c >>> +++ b/drivers/virtio/virtio.c >>> @@ -168,6 +168,12 @@ EXPORT_SYMBOL_GPL(virtio_add_status); >>> >>> const struct dma_map_ops virtio_direct_dma_ops; >>> >>> +#ifndef platform_override_dma_ops >>> +static inline void platform_override_dma_ops(struct virtio_device *vdev) >>> +{ >>> +} >>> +#endif >>> + >>> int virtio_finalize_features(struct virtio_device *dev) >>> { >>> int ret = dev->config->finalize_features(dev); >>> @@ -179,6 +185,7 @@ int virtio_finalize_features(struct virtio_device *dev) >>> if (virtio_has_iommu_quirk(dev)) >>> set_dma_ops(dev->dev.parent, &virtio_direct_dma_ops); >>> >>> + platform_override_dma_ops(dev); >> >> Is there a single place where virtio_has_iommu_quirk is called now? > > Not other than this one. But in the proposed implementation of > platform_override_dma_ops on powerpc, we will again check on > virtio_has_iommu_quirk before overriding it with SWIOTLB. > > void platform_override_dma_ops(struct virtio_device *vdev) > { > if (is_ultravisor_platform() && virtio_has_iommu_quirk(vdev)) > set_dma_ops(vdev->dev.parent, &swiotlb_dma_ops); > } > >> If so, we could put this into virtio_has_iommu_quirk then. > > Did you mean platform_override_dma_ops instead ? If so, yes that > is possible. Default implementation of platform_override_dma_ops > should just check on VIRTIO_F_IOMMU_PLATFORM feature and override > with virtio_direct_dma_ops but arch implementation can check on > what ever else they would like and override appropriately. > > Default platform_override_dma_ops will be like this > > #ifndef platform_override_dma_ops > static inline void platform_override_dma_ops(struct virtio_device *vdev) > { > if(!virtio_has_feature(vdev, VIRTIO_F_IOMMU_PLATFORM)) > set_dma_ops(dev->dev.parent, &virtio_direct_dma_ops); > } > #endif > > Proposed powerpc implementation will be like this instead > > void platform_override_dma_ops(struct virtio_device *vdev) > { > if (virtio_has_feature(vdev, VIRTIO_F_IOMMU_PLATFORM)) > return; > > if (is_ultravisor_platform()) > set_dma_ops(vdev->dev.parent, &swiotlb_dma_ops); > else > set_dma_ops(dev->dev.parent, &virtio_direct_dma_ops); > > } > > There is a redundant definition of virtio_has_iommu_quirk in the tools > directory (tools/virtio/linux/virtio_config.h) which does not seem to > be used any where. I guess that can be removed without problem. Does this sound okay ? It will merge patch 3 and 4 into a single one. On the other hand it also passes the responsibility of dealing with VIRTIO_F_IOMMU_PLATFORM flag to the architecture callback which might be bit problematic. Keeping VIRTIO_F_IOMMU_PLATFORM handling in virtio core at least makes sure that the device has a working DMA ops to fall back on if the arch hook fails to take care of it somehow.