linux-kernel - Re: [PATCH 0/8] dma-mapping: migrate to physical address-based API

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Message-ID: <39d43309-9f34-48bc-a9ad-108c607ba175@samsung.com>
Date: Tue, 8 Jul 2025 14:56:21 +0200
From: Marek Szyprowski <m.szyprowski@...sung.com>
To: Leon Romanovsky <leon@...nel.org>
Cc: Christoph Hellwig <hch@....de>, Jonathan Corbet <corbet@....net>,
	Madhavan Srinivasan <maddy@...ux.ibm.com>, Michael Ellerman
	<mpe@...erman.id.au>, Nicholas Piggin <npiggin@...il.com>, Christophe Leroy
	<christophe.leroy@...roup.eu>, Robin Murphy <robin.murphy@....com>, Joerg
	Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>, "Michael S.
	Tsirkin" <mst@...hat.com>, Jason Wang <jasowang@...hat.com>, Xuan Zhuo
 <xuanzhuo@...ux.alibaba.com>, Eugenio Pérez
 <eperezma@...hat.com>, Alexander Potapenko <glider@...gle.com>, Marco Elver
 <elver@...gle.com>, Dmitry Vyukov <dvyukov@...gle.com>, Masami Hiramatsu
 <mhiramat@...nel.org>, Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 Jérôme Glisse <jglisse@...hat.com>, Andrew Morton
 <akpm@...ux-foundation.org>, linux-doc@...r.kernel.org,
 linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
 iommu@...ts.linux.dev, virtualization@...ts.linux.dev,
 kasan-dev@...glegroups.com, linux-trace-kernel@...r.kernel.org,
 linux-mm@...ck.org, Jason Gunthorpe <jgg@...pe.ca>
Subject: Re: [PATCH 0/8] dma-mapping: migrate to physical address-based API

On 08.07.2025 14:06, Leon Romanovsky wrote:
> On Tue, Jul 08, 2025 at 01:45:20PM +0200, Marek Szyprowski wrote:
>> On 08.07.2025 13:00, Leon Romanovsky wrote:
>>> On Tue, Jul 08, 2025 at 12:27:09PM +0200, Marek Szyprowski wrote:
>>>> On 30.06.2025 15:38, Christoph Hellwig wrote:
>>>>> On Fri, Jun 27, 2025 at 08:02:13PM +0300, Leon Romanovsky wrote:
>>>>>>> Thanks for this rework! I assume that the next step is to add map_phys
>>>>>>> callback also to the dma_map_ops and teach various dma-mapping providers
>>>>>>> to use it to avoid more phys-to-page-to-phys conversions.
>>>>>> Probably Christoph will say yes, however I personally don't see any
>>>>>> benefit in this. Maybe I wrong here, but all existing .map_page()
>>>>>> implementation platforms don't support p2p anyway. They won't benefit
>>>>>> from this such conversion.
>>>>> I think that conversion should eventually happen, and rather sooner than
>>>>> later.
>>>> Agreed.
>>>>
>>>> Applied patches 1-7 to my dma-mapping-next branch. Let me know if one
>>>> needs a stable branch with it.
>>> Thanks a lot, I don't think that stable branch is needed. Realistically
>>> speaking, my VFIO DMA work won't be merged this cycle, We are in -rc5,
>>> it is complete rewrite from RFC version and touches pci-p2p code (to
>>> remove dependency on struct page) in addition to VFIO, so it will take
>>> time.
>>>
>>> Regarding, last patch (hmm), it will be great if you can take it.
>>> We didn't touch anything in hmm.c this cycle and have no plans to send PR.
>>> It can safely go through your tree.
>> Okay, then I would like to get an explicit ack from Jérôme for this.
> Jerome is not active in HMM world for a long time already.
> HMM tree is managed by us (RDMA) https://git.kernel.org/pub/scm/linux/kernel/git/rdma/rdma.git/log/?h=hmm
> ➜  kernel git:(m/dmabuf-vfio) git log --merges mm/hmm.c
> ...
> Pull HMM updates from Jason Gunthorpe:
> ...
>
> https://web.git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/?id=58ba80c4740212c29a1cf9b48f588e60a7612209
> +hmm		git	git://git.kernel.org/pub/scm/linux/kernel/git/rdma/rdma.git#hmm
>
> We just never bothered to reflect current situation in MAINTAINERS file.

Maybe this is the time to update it :)

I was just a bit confused that no-one commented the HMM patch, but if 
You maintain it, then this is okay.

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland