From: Juergen Gross <jgross@suse.com>
To: Oleksandr <olekstysh@gmail.com>,
Stefano Stabellini <sstabellini@kernel.org>
Cc: Christoph Hellwig <hch@infradead.org>,
xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org,
Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>,
Boris Ostrovsky <boris.ostrovsky@oracle.com>,
Julien Grall <julien@xen.org>,
"Michael S. Tsirkin" <mst@redhat.com>
Subject: Re: [RFC PATCH 6/6] arm/xen: Assign xen-virtio DMA ops for virtio devices in Xen guests
Date: Tue, 19 Apr 2022 16:48:03 +0200 [thread overview]
Message-ID: <b68163be-ad43-7773-22ff-e83191886626@suse.com> (raw)
In-Reply-To: <6a04cc34-fbb3-44d8-c1a4-03bda5b3deb1@gmail.com>
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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 Christoph
>>>
>>>> On Fri, Apr 15, 2022 at 03:02:45PM -0700, Stefano Stabellini wrote:
>>>>> This makes sense overall. Considering that the swiotlb-xen case and the
>>>>> virtio 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_device
xen_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.
>> - 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.
Maybe rename xen-virtio.c to grant-dma.c?
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_DMA
selected by XEN_VIRTIO.
CONFIG_XEN_VIRTIO should still guard xen_has_restricted_virtio_memory_access().
Juergen
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next prev parent reply other threads:[~2022-04-19 15:30 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-04-14 19:19 [RFC PATCH 0/6] virtio: Solution to restrict memory access under Xen using xen-virtio DMA ops layer Oleksandr Tyshchenko
2022-04-14 19:19 ` [RFC PATCH 1/6] xen/grants: support allocating consecutive grants Oleksandr Tyshchenko
2022-04-14 19:19 ` [RFC PATCH 2/6] virtio: add option to restrict memory access under Xen Oleksandr Tyshchenko
[not found] ` <5A795507-715D-494B-B56B-B12E5BE348A4@zytor.com>
2022-04-15 15:20 ` Oleksandr
[not found] ` <alpine.DEB.2.22.394.2204151235440.915916@ubuntu-linux-20-04-desktop>
2022-04-17 17:02 ` Oleksandr
2022-04-18 19:11 ` Stefano Stabellini
2022-04-19 6:21 ` Juergen Gross
2022-04-19 6:37 ` Oleksandr
2022-04-14 19:19 ` [RFC PATCH 3/6] dt-bindings: xen: Add xen, dev-domid property description for xen-virtio layer Oleksandr Tyshchenko
[not found] ` <alpine.DEB.2.22.394.2204151300130.915916@ubuntu-linux-20-04-desktop>
2022-04-17 17:24 ` [RFC PATCH 3/6] dt-bindings: xen: Add xen,dev-domid " Oleksandr
2022-04-14 19:19 ` [RFC PATCH 4/6] virtio: Various updates to xen-virtio DMA ops layer Oleksandr Tyshchenko
2022-04-15 22:02 ` Stefano Stabellini
2022-04-17 18:21 ` Oleksandr
2022-04-18 19:11 ` Stefano Stabellini
2022-04-19 6:58 ` Juergen Gross
2022-04-19 7:07 ` Oleksandr
2022-04-16 6:05 ` Christoph Hellwig
2022-04-17 18:39 ` Oleksandr
2022-04-14 19:19 ` [RFC PATCH 5/6] arm/xen: Introduce xen_setup_dma_ops() Oleksandr Tyshchenko
2022-04-15 22:02 ` Stefano Stabellini
2022-04-17 18:43 ` Oleksandr
2022-04-14 19:19 ` [RFC PATCH 6/6] arm/xen: Assign xen-virtio DMA ops for virtio devices in Xen guests Oleksandr Tyshchenko
2022-04-15 22:02 ` Stefano Stabellini
2022-04-16 6:07 ` Christoph Hellwig
2022-04-17 21:05 ` Oleksandr
2022-04-18 19:11 ` Stefano Stabellini
2022-04-19 12:17 ` Oleksandr
2022-04-19 14:48 ` Juergen Gross [this message]
2022-04-19 17:11 ` Oleksandr
2022-04-20 0:23 ` Stefano Stabellini
2022-04-20 9:00 ` Oleksandr
2022-04-20 22:49 ` Stefano Stabellini
2022-04-17 19:20 ` Oleksandr
2022-04-15 7:41 ` [RFC PATCH 0/6] virtio: Solution to restrict memory access under Xen using xen-virtio DMA ops layer Christoph Hellwig
2022-04-15 10:04 ` Oleksandr
2022-04-15 8:44 ` Michael S. Tsirkin
2022-04-15 15:29 ` Oleksandr
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