linux-kernel - Re: [PATCH 2/2] dma-mapping: force unencryped devices are always addressing limited

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Date:   Thu, 28 Nov 2019 16:36:46 +0100
From:   "hch@....de" <hch@....de>
To:     Thomas Hellstrom <thellstrom@...are.com>
Cc:     "hch@....de" <hch@....de>,
        "thomas.lendacky@....com" <thomas.lendacky@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "christian.koenig@....com" <christian.koenig@....com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Subject: Re: [PATCH 2/2] dma-mapping: force unencryped devices are always
 addressing limited

On Thu, Nov 28, 2019 at 08:02:16AM +0000, Thomas Hellstrom wrote:
> > We have a hard time handling that in generic code.  Do we have any
> > good use case for SWIOTLB_FORCE not that we have force_dma_unencrypted?
> > I'd love to be able to get rid of it..
> >
> IIRC the justification for it is debugging. Drivers that don't do
> syncing correctly or have incorrect assumptions of initialization of DMA
> memory will not work properly when SWIOTLB is forced. We recently found
> a vmw_pvscsi device flaw that way...

Ok. I guess debugging is reasonable.  Although that means I need
to repsin this quite a bit as I now need a callout to dma_direct.
I'll respin it in the next days.