linux-kernel - Re: [PATCH] virtio: Force DMA restricted devices through DMA API

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Message-ID: <YtePv+AT+pqD2wHe@infradead.org>
Date:   Tue, 19 Jul 2022 22:16:47 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Keir Fraser <keirf@...gle.com>
Cc:     Christoph Hellwig <hch@...radead.org>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>, kernel-team@...roid.com,
        virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] virtio: Force DMA restricted devices through DMA API

On Tue, Jul 19, 2022 at 04:11:50PM +0000, Keir Fraser wrote:
> Well here are two possible approaches:
> 
> 1. Revert e41b1355508d outright. I'm not even sure what it would mean
> for reported pages to go through IOMMU. And VIRTIO_F_ACCESS_PLATFORM
> is no longer IOMMU-specific anyway.
> 
> 2. Continue to clear the flag during virtio_balloon negotiation, but
> remember that it was offered, and test for that in vring_use_dma_api()
> as well as, or instead of, virtio_has_dma_quirk().
> 
> Do either of those appeal?

I'll have to defer to people that actually understand the virtio_balloon
code, because I haven't evey seriously looked at it.