linux-kernel - Re: [PATCH v1 06/16] iommu/dma: extend iommu_dma_*map

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Message-ID: <20250807120715.GF184255@nvidia.com>
Date: Thu, 7 Aug 2025 09:07:15 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: Leon Romanovsky <leon@...nel.org>
Cc: Marek Szyprowski <m.szyprowski@...sung.com>,
	Leon Romanovsky <leonro@...dia.com>,
	Abdiel Janulgue <abdiel.janulgue@...il.com>,
	Alexander Potapenko <glider@...gle.com>,
	Alex Gaynor <alex.gaynor@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Christoph Hellwig <hch@....de>, Danilo Krummrich <dakr@...nel.org>,
	iommu@...ts.linux.dev, Jason Wang <jasowang@...hat.com>,
	Jens Axboe <axboe@...nel.dk>, Joerg Roedel <joro@...tes.org>,
	Jonathan Corbet <corbet@....net>, Juergen Gross <jgross@...e.com>,
	kasan-dev@...glegroups.com, Keith Busch <kbusch@...nel.org>,
	linux-block@...r.kernel.org, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	linux-nvme@...ts.infradead.org, linuxppc-dev@...ts.ozlabs.org,
	linux-trace-kernel@...r.kernel.org,
	Madhavan Srinivasan <maddy@...ux.ibm.com>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Michael Ellerman <mpe@...erman.id.au>,
	"Michael S. Tsirkin" <mst@...hat.com>,
	Miguel Ojeda <ojeda@...nel.org>,
	Robin Murphy <robin.murphy@....com>, rust-for-linux@...r.kernel.org,
	Sagi Grimberg <sagi@...mberg.me>,
	Stefano Stabellini <sstabellini@...nel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	virtualization@...ts.linux.dev, Will Deacon <will@...nel.org>,
	xen-devel@...ts.xenproject.org
Subject: Re: [PATCH v1 06/16] iommu/dma: extend iommu_dma_*map_phys API to
 handle MMIO memory

On Mon, Aug 04, 2025 at 03:42:40PM +0300, Leon Romanovsky wrote:
> From: Leon Romanovsky <leonro@...dia.com>
> 
> Combine iommu_dma_*map_phys with iommu_dma_*map_resource interfaces in
> order to allow single phys_addr_t flow.

Some later patch deletes iommu_dma_map_resource() ? Mention that plan here?

> --- a/drivers/iommu/dma-iommu.c
> +++ b/drivers/iommu/dma-iommu.c
> @@ -1193,12 +1193,17 @@ static inline size_t iova_unaligned(struct iova_domain *iovad, phys_addr_t phys,
>  dma_addr_t iommu_dma_map_phys(struct device *dev, phys_addr_t phys, size_t size,
>  		enum dma_data_direction dir, unsigned long attrs)
>  {
> -	bool coherent = dev_is_dma_coherent(dev);
> -	int prot = dma_info_to_prot(dir, coherent, attrs);
>  	struct iommu_domain *domain = iommu_get_dma_domain(dev);
>  	struct iommu_dma_cookie *cookie = domain->iova_cookie;
>  	struct iova_domain *iovad = &cookie->iovad;
>  	dma_addr_t iova, dma_mask = dma_get_mask(dev);
> +	bool coherent;
> +	int prot;
> +
> +	if (attrs & DMA_ATTR_MMIO)
> +		return __iommu_dma_map(dev, phys, size,
> +				dma_info_to_prot(dir, false, attrs) | IOMMU_MMIO,
> +				dma_get_mask(dev));

I realize that iommu_dma_map_resource() doesn't today, but shouldn't
this be checking for swiotlb:

	if (dev_use_swiotlb(dev, size, dir) &&
	    iova_unaligned(iovad, phys, size)) {

Except we have to fail for ATTR_MMIO?

Now that we have ATTR_MMIO, should dma_info_to_prot() just handle it
directly instead of open coding the | IOMMU_MMIO and messing with the
coherent attribute?

Jason