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From:   Viresh Kumar <viresh.kumar@linaro.org>
Date:   Wed, 15 Jun 2022 11:53:54 +0530
Message-ID: <CAOh2x=kxpdisV+tqcYOoZGSKA8YjPMej+7u19Jpa1jmVcZCaxA@mail.gmail.com>
Subject: Re: [PATCH V4 0/8] virtio: Solution to restrict memory access under
 Xen using xen-grant DMA-mapping layer
To:     Oleksandr Tyshchenko <olekstysh@gmail.com>
Cc:     xen-devel@lists.xenproject.org,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        virtualization@lists.linux-foundation.org, x86@kernel.org,
        Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>,
        "Michael S. Tsirkin" <mst@redhat.com>,
        Christoph Hellwig <hch@infradead.org>,
        Stefano Stabellini <sstabellini@kernel.org>,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        Juergen Gross <jgross@suse.com>, Julien Grall <julien@xen.org>,
        Bertrand Marquis <bertrand.marquis@arm.com>,
        Wei Chen <Wei.Chen@arm.com>, Henry Wang <Henry.Wang@arm.com>,
        Kaly Xin <Kaly.Xin@arm.com>, Jiamei Xie <Jiamei.Xie@arm.com>,
        =?UTF-8?B?QWxleCBCZW5uw6ll?= <alex.bennee@linaro.org>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Mathieu Poirier <mathieu.poirier@linaro.org>
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Hi Oleksandr,

On Mon, Jun 6, 2022 at 10:16 AM Oleksandr Tyshchenko
<olekstysh@gmail.com> wrote:
> The high level idea is to create new Xen=E2=80=99s grant table based DMA-=
mapping layer for the guest Linux whose main
> purpose is to provide a special 64-bit DMA address which is formed by usi=
ng the grant reference (for a page
> to be shared with the backend) with offset and setting the highest addres=
s bit (this is for the backend to
> be able to distinguish grant ref based DMA address from normal GPA). For =
this to work we need the ability
> to allocate contiguous (consecutive) grant references for multi-page allo=
cations. And the backend then needs
> to offer VIRTIO_F_ACCESS_PLATFORM and VIRTIO_F_VERSION_1 feature bits (it=
 must support virtio-mmio modern
> transport for 64-bit addresses in the virtqueue).

I was trying your series, from Linus's tree now and started seeing
boot failures,
failed to mount rootfs. And the reason probably is these messages:

[ 1.222498] virtio_scsi virtio1: device must provide VIRTIO_F_ACCESS_PLATFO=
RM
[ 1.316334] virtio_net virtio0: device must provide VIRTIO_F_ACCESS_PLATFOR=
M

I understand from your email that the backends need to offer
VIRTIO_F_ACCESS_PLATFORM flag now, but should this requirement be a
bit soft ? I mean shouldn't we allow both types of backends to run with the=
 same
kernel, ones that offer this feature and others that don't ? The ones that =
don't
offer the feature, should continue to work like they used to, i.e.
without the restricted
memory access feature.

I am testing Xen currently with help of Qemu  over my x86 desktop and
these backends
(scsi and net) are part of QEMU itself I think, and I don't really
want to go and make the
change there.

Thanks.

--
Viresh