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From: Thomas Hellstrom via iommu <iommu@lists.linux-foundation.org>
To: "hch@lst.de" <hch@lst.de>
Cc: "thomas.lendacky@amd.com" <thomas.lendacky@amd.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"linux-mm@kvack.org" <linux-mm@kvack.org>,
	"iommu@lists.linux-foundation.org"
	<iommu@lists.linux-foundation.org>,
	"christian.koenig@amd.com" <christian.koenig@amd.com>
Subject: Re: [PATCH 2/2] dma-mapping: force unencryped devices are always addressing limited
Date: Thu, 28 Nov 2019 08:02:16 +0000
Message-ID: <MN2PR05MB6141B6D7E28A146EBF9CE79FA1470@MN2PR05MB6141.namprd05.prod.outlook.com> (raw)
In-Reply-To: <20191128075153.GD20659@lst.de>

On 11/28/19 8:51 AM, hch@lst.de wrote:
> On Wed, Nov 27, 2019 at 06:22:57PM +0000, Thomas Hellstrom wrote:
>>>  bool dma_addressing_limited(struct device *dev)
>>>  {
>>> +	if (force_dma_unencrypted(dev))
>>> +		return true;
>>>  	return min_not_zero(dma_get_mask(dev), dev->bus_dma_limit) <
>>>  			    dma_get_required_mask(dev);
>>>  }
>> Any chance to have the case
>>
>> (swiotlb_force == SWIOTLB_FORCE)
>>
>> also included?
> 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...

/Thomas



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Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-11-27 14:40 make dma_addressing_limited work for memory encryption setups Christoph Hellwig
2019-11-27 14:40 ` [PATCH 1/2] dma-mapping: move dma_addressing_limited out of line Christoph Hellwig
2019-11-27 17:13   ` Matthew Wilcox
2019-11-27 14:40 ` [PATCH 2/2] dma-mapping: force unencryped devices are always addressing limited Christoph Hellwig
2019-11-27 18:22   ` Thomas Hellstrom via iommu
2019-11-28  7:51     ` hch
2019-11-28  8:02       ` Thomas Hellstrom via iommu [this message]
2019-11-28 15:36         ` hch
2019-12-04 13:03 make dma_addressing_limited work for memory encryption setups v2 Christoph Hellwig
2019-12-04 13:03 ` [PATCH 2/2] dma-mapping: force unencryped devices are always addressing limited Christoph Hellwig
2019-12-06 14:10   ` Thomas Hellstrom via iommu

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