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

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Message-ID: <YtbRwO40CmIRWOUR@google.com>
Date:   Tue, 19 Jul 2022 15:46:08 +0000
From:   Keir Fraser <keirf@...gle.com>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     "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 08:23:28AM -0700, Christoph Hellwig wrote:
> On Tue, Jul 19, 2022 at 10:02:56AM +0000, Keir Fraser wrote:
> > +#include <linux/swiotlb.h>
> 
> Drivers must never use this header.  We have a few pre-existing abuses
> in the drm code, but they will go away.
> 

Ok fair enough, and I'll admit I don't like my use of
swiotlb_for_alloc() a lot either.

However, if the general idea at least is acceptable, would the
implementation be acceptable if I add an explicit API for this to the
DMA subsystem, and hide the detail there?

Or a completely different approach would be to revert the patch
e41b1355508d which clears VIRTIO_F_ACCESS_PLATFORM in the balloon
driver. MST: That's back in your court, as it's your patch!