From: Oleksandr <olekstysh@gmail.com>
To: Juergen Gross <jgross@suse.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 20:11:12 +0300 [thread overview]
Message-ID: <5afb9e61-4164-9cc9-278a-911fc21f4f6c@gmail.com> (raw)
In-Reply-To: <b68163be-ad43-7773-22ff-e83191886626@suse.com>
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 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.
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_DMA
> selected 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
next prev parent reply other threads:[~2022-04-19 17:12 UTC|newest]
Thread overview: 40+ 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
2022-04-14 19:43 ` H. Peter Anvin
2022-04-15 15:20 ` Oleksandr
2022-04-15 22:01 ` Stefano Stabellini
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
2022-04-15 22:01 ` Stefano Stabellini
2022-04-17 17:24 ` 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
2022-04-19 17:11 ` Oleksandr [this message]
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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