From: Christoph Hellwig <hch@lst.de>
To: Lu Baolu <baolu.lu@linux.intel.com>
Cc: kevin.tian@intel.com, ashok.raj@intel.com,
linux-kernel@vger.kernel.org, Daniel Drake <drake@endlessm.com>,
iommu@lists.linux-foundation.org,
Robin Murphy <robin.murphy@arm.com>,
Christoph Hellwig <hch@lst.de>,
Derrick Jonathan <jonathan.derrick@intel.com>
Subject: Re: [PATCH v3 1/3] iommu/vt-d: Allow 32bit devices to uses DMA domain
Date: Fri, 17 Apr 2020 08:50:54 +0200 [thread overview]
Message-ID: <20200417065054.GA18880@lst.de> (raw)
In-Reply-To: <e11d8138-f704-2f5e-c0b1-70b367a33d5d@linux.intel.com>
On Thu, Apr 16, 2020 at 03:40:38PM +0800, Lu Baolu wrote:
>> description. I'd need to look at the final code, but it seems like
>> this will still cause bounce buffering instead of using dynamic
>> mapping, which still seems like an awful idea.
>
> Yes. If the user chooses to use identity domain by default through
> kernel command, identity domain will be applied for all devices. For
> those devices with limited addressing capability, bounce buffering will
> be used when they try to access the memory beyond their address
> capability. This won't cause any kernel regression as far as I can see.
>
> Switching domain during runtime with drivers loaded will cause real
> problems as I said in the commit message. That's the reason why I am
> proposing to remove it. If we want to keep it, we have to make sure that
> switching domain for one device should not impact other devices which
> share the same domain with it. Furthermore, it's better to implement it
> in the generic layer to keep device driver behavior consistent on all
> architectures.
I don't disagree with the technical points. What I pointed out is that
a) the actual technical change is not in the commit log, which it
should be
b) that I still think taking away the ability to dynamically map
devices in the identify domain after all the time we allowed for
that is going to cause nasty regressions.
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next prev parent reply other threads:[~2020-04-17 6:51 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-16 6:23 [PATCH v3 0/3] Replace private domain with per-group default domain Lu Baolu
2020-04-16 6:23 ` [PATCH v3 1/3] iommu/vt-d: Allow 32bit devices to uses DMA domain Lu Baolu
2020-04-16 7:01 ` Christoph Hellwig
2020-04-16 7:40 ` Lu Baolu
2020-04-17 6:50 ` Christoph Hellwig [this message]
2020-04-17 12:49 ` Lu Baolu
2020-04-16 6:23 ` [PATCH v3 2/3] iommu/vt-d: Allow PCI sub-hierarchy to use " Lu Baolu
2020-04-16 6:23 ` [PATCH v3 3/3] iommu/vt-d: Apply per-device dma_ops Lu Baolu
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