Re: [PATCH 1/1] iommu/vt-d: use DMA domain for real DMA devices and subdevices

From: Lu Baolu <baolu.lu@linux.intel.com>
To: Daniel Drake <drake@endlessm.com>
Cc: Linux PCI <linux-pci@vger.kernel.org>,
	iommu@lists.linux-foundation.org,
	Bjorn Helgaas <helgaas@kernel.org>,
	Linux Upstreaming Team <linux@endlessm.com>,
	Jon Derrick <jonathan.derrick@intel.com>
Subject: Re: [PATCH 1/1] iommu/vt-d: use DMA domain for real DMA devices and subdevices
Date: Mon, 13 Apr 2020 10:48:55 +0800	[thread overview]
Message-ID: <32cc4809-7029-bc5e-5a74-abbe43596e8d@linux.intel.com> (raw)
In-Reply-To: <CAD8Lp45dJ3-t6qqctiP1a=c44PEWZ-L04yv0r0=1Nrvwfouz1w@mail.gmail.com>

Hi Daniel,

On 2020/4/13 10:25, Daniel Drake wrote:
> On Fri, Apr 10, 2020 at 9:22 AM Lu Baolu <baolu.lu@linux.intel.com> wrote:
>> This is caused by the fragile private domain implementation. We are in
>> process of removing it by enhancing the iommu subsystem with per-group
>> default domain.
>>
>> https://www.spinics.net/lists/iommu/msg42976.html
>>
>> So ultimately VMD subdevices should have their own per-device iommu data
>> and support per-device dma ops.
> 
> Interesting. There's also this patchset you posted:
> [PATCH 00/19] [PULL REQUEST] iommu/vt-d: patches for v5.7
> https://lists.linuxfoundation.org/pipermail/iommu/2020-April/042967.html
> (to be pushed out to 5.8)

Both are trying to solve a same problem.

I have sync'ed with Joerg. This patch set will be replaced with Joerg's
proposal due to a race concern between domain switching and driver
binding. I will rebase all vt-d patches in this set on top of Joerg's
change.

Best regards,
baolu

> 
> In there you have:
>> iommu/vt-d: Don't force 32bit devices to uses DMA domain
> which seems to clash with the approach being explored in this thread.
> 
> And:
>> iommu/vt-d: Apply per-device dma_ops
> This effectively solves the trip point that caused me to open these
> discussions, where intel_map_page() -> iommu_need_mapping() would
> incorrectly determine that a intel-iommu DMA mapping was needed for a
> PCI subdevice running in identity mode. After this patch, a PCI
> subdevice in identity mode uses the default system dma_ops and
> completely avoids intel-iommu.
> 
> So that solves the issues I was looking at. Jon, you might want to
> check if the problems you see are likewise solved for you by these
> patches.
> 
> I didn't try Joerg's iommu group rework yet as it conflicts with those
> patches above.
> 
> Daniel
> 
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