[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [RFC PATCH 6/6] arm/xen: Assign xen-virtio DMA ops for virtio devices in Xen guests
Hello Stefano, Juergen On 19.04.22 17:48, Juergen Gross wrote: On 19.04.22 14:17, Oleksandr wrote:Hello Stefano, Juergen On 18.04.22 22:11, Stefano Stabellini wrote:On Mon, 18 Apr 2022, Oleksandr wrote:On 16.04.22 09:07, Christoph Hellwig wrote: Hello ChristophOn Fri, Apr 15, 2022 at 03:02:45PM -0700, Stefano Stabellini wrote:This makes sense overall. Considering that the swiotlb-xen case and thevirtio case are mutually exclusive, I would write it like this:Curious question: Why can't the same grant scheme also be used for non-virtio devices? I really hate having virtio hooks in the arch dma code. Why can't Xen just say in DT/ACPI that grants can be used for a given device?[...]This patch series tries to make things work with "virtio" devices in Xen system without introducing any modifications to code under drivers/virtio.Actually, I think Christoph has a point. There is nothing inherently virtio specific in this patch series or in the "xen,dev-domid" device tree binding.Although the main intention of this series was to enable using virtio devices in Xen guests, I agree that nothing in new DMA ops layer (xen-virtio.c) is virtio specific (at least at the moment). Regarding the whole patch series I am not quite sure, as it uses arch_has_restricted_virtio_memory_access(). >Assuming a given device is emulated by a Xen backend, it could be used with grants as well. For instance, we could provide an emulated e1000 NIC with a "xen,dev-domid" property in device tree. Linux could use grants with it and the backend could map the grants. It would work the same way as virtio-net/block/etc. Passthrough devices wouldn't have the "xen,dev-domid" property, so no problems. So I think we could easily generalize this work and expand it to any device. We just need to hook on the "xen,dev-domid" device tree property. I think it is just a matter of: - remove the "virtio,mmio" check from xen_is_virtio_device - rename xen_is_virtio_device to something more generic, like xen_is_grants_devicexen_is_grants_dma_device, please. Normal Xen PV devices are covered by grants, too, and I'd like to avoid the confusion arising from this. yes, this definitely makes sense as we need to distinguish - rename xen_virtio_setup_dma_ops to something more generic, like xen_grants_setup_dma_ops And that's pretty much it.+ likely renaming everything in that patch series not to mention virtio (mostly related to xen-virtio.c internals).Stefano, thank you for clarifying Christoph's point.Well, I am not against going this direction. Could we please make a decision on this? @Juergen, what is your opinion?Yes, why not. ok, thank you for confirming. Maybe rename xen-virtio.c to grant-dma.c? Personally I don't mind. I'd keep the XEN_VIRTIO related config option, as this will be the normal use case. grant-dma.c should be covered by a new hidden config option XEN_GRANT_DMAselected by XEN_VIRTIO. I got it, ok CONFIG_XEN_VIRTIO should still guard xen_has_restricted_virtio_memory_access(). ok So a few questions to clarify:1. What is the best place to keep "xen,dev-domid" binding's description now? I think that proposed in current series place (Documentation/devicetree/bindings/virtio/) is not good fit now. 2. I assume the logic in the current patch will remain the same, I mean we will still assign Xen grant DMA ops from xen_setup_dma_ops() here? Juergen -- Regards, Oleksandr Tyshchenko
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