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SubjectRe: [RFC 4/4] virtio: Add platform specific DMA API translation for virito devices
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/

> 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 <khandual@linux.vnet.ibm.com>
> ---
> 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 <linux/of.h>
> #include <linux/iommu.h>
> #include <linux/rculist.h>
> +#include <linux/virtio.h>
> #include <asm/io.h>
> #include <asm/prom.h>
> #include <asm/rtas.h>
> @@ -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?
If so, we could put this into virtio_has_iommu_quirk then.

> if (!virtio_has_feature(dev, VIRTIO_F_VERSION_1))
> return 0;
>
> --
> 2.9.3

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