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Subject: Re: [PATCH v15 06/12] swiotlb: Use is_swiotlb_force_bounce for
 swiotlb data bouncing
To:     Christoph Hellwig <hch@lst.de>
Cc:     Will Deacon <will@kernel.org>, heikki.krogerus@linux.intel.com,
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From:   Robin Murphy <robin.murphy@arm.com>
Message-ID: <bb32d5a6-2b34-4524-e171-3e9f5f4d3a94@arm.com>
Date:   Tue, 6 Jul 2021 16:39:11 +0100
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On 2021-07-06 15:05, Christoph Hellwig wrote:
> On Tue, Jul 06, 2021 at 03:01:04PM +0100, Robin Murphy wrote:
>> FWIW I was pondering the question of whether to do something along those
>> lines or just scrap the default assignment entirely, so since I hadn't got
>> round to saying that I've gone ahead and hacked up the alternative
>> (similarly untested) for comparison :)
>>
>> TBH I'm still not sure which one I prefer...
> 
> Claire did implement something like your suggestion originally, but
> I don't really like it as it doesn't scale for adding multiple global
> pools, e.g. for the 64-bit addressable one for the various encrypted
> secure guest schemes.

Ah yes, that had slipped my mind, and it's a fair point indeed. Since 
we're not concerned with a minimal fix for backports anyway I'm more 
than happy to focus on Will's approach. Another thing is that that looks 
to take us a quiet step closer to the possibility of dynamically 
resizing a SWIOTLB pool, which is something that some of the hypervisor 
protection schemes looking to build on top of this series may want to 
explore at some point.

Robin.