From: Stefano Stabellini <sstabellini@kernel.org>
To: Oleksandr <olekstysh@gmail.com>
Cc: Juergen Gross <jgross@suse.com>,
Stefano Stabellini <sstabellini@kernel.org>,
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 17:23:40 -0700 (PDT) [thread overview]
Message-ID: <alpine.DEB.2.22.394.2204191717020.915916@ubuntu-linux-20-04-desktop> (raw)
In-Reply-To: <5afb9e61-4164-9cc9-278a-911fc21f4f6c@gmail.com>
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On Tue, 19 Apr 2022, Oleksandr wrote:
> 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.
I would probably add it to the existing
Documentation/devicetree/bindings/arm/xen.txt.
> 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?
Yes I think so
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next prev parent reply other threads:[~2022-04-20 0:25 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
2022-04-19 17:11 ` Oleksandr
2022-04-20 0:23 ` Stefano Stabellini [this message]
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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