linux-kernel - Re: [RFC PATCH v3 4/6] swiotlb: Add restricted DMA alloc/free support.

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Date:   Wed, 13 Jan 2021 19:32:18 +0100
From:   Christoph Hellwig <hch@....de>
To:     Robin Murphy <robin.murphy@....com>
Cc:     Christoph Hellwig <hch@....de>,
        Claire Chang <tientzu@...omium.org>, robh+dt@...nel.org,
        mpe@...erman.id.au, benh@...nel.crashing.org, paulus@...ba.org,
        joro@...tes.org, will@...nel.org, frowand.list@...il.com,
        konrad.wilk@...cle.com, boris.ostrovsky@...cle.com,
        jgross@...e.com, sstabellini@...nel.org, m.szyprowski@...sung.com,
        grant.likely@....com, xypron.glpk@....de, treding@...dia.com,
        mingo@...nel.org, bauerman@...ux.ibm.com, peterz@...radead.org,
        gregkh@...uxfoundation.org, saravanak@...gle.com,
        rafael.j.wysocki@...el.com, heikki.krogerus@...ux.intel.com,
        andriy.shevchenko@...ux.intel.com, rdunlap@...radead.org,
        dan.j.williams@...el.com, bgolaszewski@...libre.com,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, iommu@...ts.linux-foundation.org,
        xen-devel@...ts.xenproject.org, tfiga@...omium.org,
        drinkcat@...omium.org
Subject: Re: [RFC PATCH v3 4/6] swiotlb: Add restricted DMA alloc/free
 support.

On Wed, Jan 13, 2021 at 06:27:08PM +0000, Robin Murphy wrote:
>> Can we hook in somewhat lower level in the dma-direct code so that all
>> the remapping in dma-direct can be reused instead of duplicated?  That
>> also becomes important if we want to use non-remapping uncached support,
>> e.g. on mips or x86, or the direct changing of the attributes that Will
>> planned to look into for arm64.
>
> Indeed, AFAICS this ought to boil down to a direct equivalent of 
> __dma_direct_alloc_pages() - other than the address there should be no 
> conceptual difference between pages from the restricted pool and those from 
> the regular page allocator, so this probably deserves to be plumbed in as 
> an alternative to that.

Yes, that's what I mean.  You managed to word it much better, though.