linux-kernel - Re: [RFC] virtio: support VIRTIO_F_IO

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Message-ID: <20180503090652.GB5301@stefanha-x1.localdomain>
Date:   Thu, 3 May 2018 10:06:52 +0100
From:   Stefan Hajnoczi <stefanha@...hat.com>
To:     Tiwei Bie <tiwei.bie@...el.com>
Cc:     mst@...hat.com, jasowang@...hat.com, pbonzini@...hat.com,
        virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, dan.daly@...el.com,
        cunming.liang@...el.com, zhihong.wang@...el.com
Subject: Re: [RFC] virtio: support VIRTIO_F_IO_BARRIER

On Thu, May 03, 2018 at 10:59:55AM +0800, Tiwei Bie wrote:
> This patch introduces the support for VIRTIO_F_IO_BARRIER.
> When this feature is negotiated, driver will use the barriers
> suitable for hardware devices.
> 
> Signed-off-by: Tiwei Bie <tiwei.bie@...el.com>

I should have thought of this earlier, but why is a new feature bit
necessary?  If a hardware virtio device is in use, then the device
should already negotiate VIRTIO_F_IOMMU_PLATFORM (i.e. use DMA APIs and
IOMMU callbacks).

Does disabling weak_barriers when VIRTIO_F_IOMMU_PLATFORM is set solve
the problem?

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