linux-kernel - Re: [PATCH v9 03/24] iommu: generalize the batched sync after map interface

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Message-ID: <20250423171537.GJ1213339@ziepe.ca>
Date: Wed, 23 Apr 2025 14:15:37 -0300
From: Jason Gunthorpe <jgg@...pe.ca>
To: Leon Romanovsky <leon@...nel.org>
Cc: Marek Szyprowski <m.szyprowski@...sung.com>,
	Jens Axboe <axboe@...nel.dk>, Christoph Hellwig <hch@....de>,
	Keith Busch <kbusch@...nel.org>, Jake Edge <jake@....net>,
	Jonathan Corbet <corbet@....net>, Zhu Yanjun <zyjzyj2000@...il.com>,
	Robin Murphy <robin.murphy@....com>, Joerg Roedel <joro@...tes.org>,
	Will Deacon <will@...nel.org>, Sagi Grimberg <sagi@...mberg.me>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Logan Gunthorpe <logang@...tatee.com>,
	Yishai Hadas <yishaih@...dia.com>,
	Shameer Kolothum <shameerali.kolothum.thodi@...wei.com>,
	Kevin Tian <kevin.tian@...el.com>,
	Alex Williamson <alex.williamson@...hat.com>,
	Jérôme Glisse <jglisse@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-block@...r.kernel.org, linux-rdma@...r.kernel.org,
	iommu@...ts.linux.dev, linux-nvme@...ts.infradead.org,
	linux-pci@...r.kernel.org, kvm@...r.kernel.org, linux-mm@...ck.org,
	Niklas Schnelle <schnelle@...ux.ibm.com>,
	Chuck Lever <chuck.lever@...cle.com>,
	Luis Chamberlain <mcgrof@...nel.org>,
	Matthew Wilcox <willy@...radead.org>,
	Dan Williams <dan.j.williams@...el.com>,
	Kanchan Joshi <joshi.k@...sung.com>,
	Chaitanya Kulkarni <kch@...dia.com>,
	Leon Romanovsky <leonro@...dia.com>
Subject: Re: [PATCH v9 03/24] iommu: generalize the batched sync after map
 interface

On Wed, Apr 23, 2025 at 11:12:54AM +0300, Leon Romanovsky wrote:
> From: Christoph Hellwig <hch@....de>
> 
> For the upcoming IOVA-based DMA API we want to use the interface batch the
> sync after mapping multiple entries from dma-iommu without having a
> scatterlist.

Grammer:

 For the upcoming IOVA-based DMA API we want to batch the
 ops->iotlb_sync_map() call after mapping multiple IOVAs from
 dma-iommu without having a scatterlist. Improve the API.

 Add a wrapper for the map_sync as iommu_sync_map() so that callers don't
 need to poke into the methods directly.

 Formalize __iommu_map() into iommu_map_nosync() which requires the
 caller to call iommu_sync_map() after all maps are completed.

 Refactor the existing sanity checks from all the different layers
 into iommu_map_nosync().

>  drivers/iommu/iommu.c | 65 +++++++++++++++++++------------------------
>  include/linux/iommu.h |  4 +++
>  2 files changed, 33 insertions(+), 36 deletions(-)

Reviewed-by: Jason Gunthorpe <jgg@...dia.com>

> +	/* Discourage passing strange GFP flags */
> +	if (WARN_ON_ONCE(gfp & (__GFP_COMP | __GFP_DMA | __GFP_DMA32 |
> +				__GFP_HIGHMEM)))
> +		return -EINVAL;

There is some kind of overlap with the new iommu_alloc_pages_node()
here that does a similar check, nothing that can be addressed in this
series but maybe a TBD for later..

Jason