linux-kernel - Re: [PATCH v5 04/27] iommu/io-pgtable-arm: Factor kernel specific code out

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Message-ID: <aUHmXkdehGGYX5Mg@google.com>
Date: Tue, 16 Dec 2025 23:08:14 +0000
From: Mostafa Saleh <smostafa@...gle.com>
To: Jason Gunthorpe <jgg@...pe.ca>
Cc: linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	kvmarm@...ts.linux.dev, iommu@...ts.linux.dev,
	catalin.marinas@....com, will@...nel.org, maz@...nel.org,
	oliver.upton@...ux.dev, joey.gouly@....com, suzuki.poulose@....com,
	yuzenghui@...wei.com, joro@...tes.org, jean-philippe@...aro.org,
	praan@...gle.com, danielmentz@...gle.com, mark.rutland@....com,
	qperret@...gle.com, tabba@...gle.com
Subject: Re: [PATCH v5 04/27] iommu/io-pgtable-arm: Factor kernel specific
 code out

On Mon, Dec 15, 2025 at 08:58:34PM -0400, Jason Gunthorpe wrote:
> On Fri, Dec 12, 2025 at 03:37:43PM +0000, Mostafa Saleh wrote:
> > On Fri, Nov 28, 2025 at 12:45:41PM -0400, Jason Gunthorpe wrote:
> > > On Mon, Nov 17, 2025 at 06:47:51PM +0000, Mostafa Saleh wrote:
> > > > Some of the used APIs are only part of the kernel and are not
> > > > available in the hypervisor, factor those out:
> > > > - alloc/free memory
> > > 
> > > Why not provide the iommu-pages API for the hypervisor environment?
> > > 
> > > Same for virt_to_phys, that could be moved into an iommu-pages wrapper
> > > too..
> > 
> > I guess that's possible, but then we would have to stub dma_map/unmap,
> > which might a bit ugly. I will look more into it.
> 
> I am hoping to drop the dma_map/unmap and replace it with an arch
> cache flush call directly since the code is no longer modular and
> relying on the DMA API will have some problems with a future patch
> series I'm expecting..
> 

I see, I always wondered about that, it's because CMO are not exported
for modules, I can look more into it and send a separate clean up.

Thanks,
Mostafa

> Jason