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From: Christoph Hellwig <hch@lst.de>
To: Lu Baolu <baolu.lu@linux.intel.com>
Cc: David Woodhouse <dwmw2@infradead.org>,
	Joerg Roedel <joro@8bytes.org>,
	ashok.raj@intel.com, jacob.jun.pan@intel.com,
	kevin.tian@intel.com, Christoph Hellwig <hch@lst.de>,
	Robin Murphy <robin.murphy@arm.com>,
	iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org,
	Jacob Pan <jacob.jun.pan@linux.intel.com>
Subject: Re: [PATCH 2/3] iommu/vt-d: Apply per-device dma_ops
Date: Tue, 6 Aug 2019 08:43:47 +0200	[thread overview]
Message-ID: <20190806064347.GA14906@lst.de> (raw)
In-Reply-To: <20190801060156.8564-3-baolu.lu@linux.intel.com>

Hi Lu,

I really do like the switch to the per-device dma_map_ops, but:

On Thu, Aug 01, 2019 at 02:01:55PM +0800, Lu Baolu wrote:
> Current Intel IOMMU driver sets the system level dma_ops. This
> implementation has at least the following drawbacks: 1) each
> dma API will go through the IOMMU driver even the devices are
> using identity mapped domains; 2) if user requests to use an
> identity mapped domain (a.k.a. bypass iommu translation), the
> driver might fall back to dma domain blindly if the device is
> not able to address all system memory.

This is very clearly a behavioral regression.  The intel-iommu driver
has always used the iommu mapping to provide decent support for
devices that do not have the full 64-bit addressing capability, and
changing this will make a lot of existing setups go slower.

I don't think having to use swiotlb for these devices helps anyone.

  reply	other threads:[~2019-08-06  6:43 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-01  6:01 [PATCH 0/3] iommu/vtd: Per device dma ops Lu Baolu
2019-08-01  6:01 ` [PATCH 1/3] iommu/vt-d: Refactor find_domain() helper Lu Baolu
2019-08-01  6:10   ` Christoph Hellwig
2019-08-01  6:20     ` Lu Baolu
2019-08-01 14:09       ` Christoph Hellwig
2019-08-02  2:06         ` Lu Baolu
2019-08-01  6:01 ` [PATCH 2/3] iommu/vt-d: Apply per-device dma_ops Lu Baolu
2019-08-06  6:43   ` Christoph Hellwig [this message]
2019-08-07  3:06     ` Lu Baolu
2019-08-13  7:38       ` Lu Baolu
2019-08-01  6:01 ` [PATCH 3/3] iommu/vt-d: Cleanup after using per-device dma ops Lu Baolu

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