linux-kernel - Re: [PATCH v9 17/24] vfio/mlx5: Enable the DMA link API

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20250423180941.GS1213339@ziepe.ca>
Date: Wed, 23 Apr 2025 15:09:41 -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>,
	Leon Romanovsky <leonro@...dia.com>, 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>
Subject: Re: [PATCH v9 17/24] vfio/mlx5: Enable the DMA link API

On Wed, Apr 23, 2025 at 11:13:08AM +0300, Leon Romanovsky wrote:
> From: Leon Romanovsky <leonro@...dia.com>
> 
> Remove intermediate scatter-gather table completely and
> enable new DMA link API.
> 
> Tested-by: Jens Axboe <axboe@...nel.dk>
> Signed-off-by: Leon Romanovsky <leonro@...dia.com>
> ---
>  drivers/vfio/pci/mlx5/cmd.c  | 298 ++++++++++++++++-------------------
>  drivers/vfio/pci/mlx5/cmd.h  |  21 ++-
>  drivers/vfio/pci/mlx5/main.c |  31 ----
>  3 files changed, 147 insertions(+), 203 deletions(-)

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

> +static int register_dma_pages(struct mlx5_core_dev *mdev, u32 npages,
> +			      struct page **page_list, u32 *mkey_in,
> +			      struct dma_iova_state *state,
> +			      enum dma_data_direction dir)
> +{
> +	dma_addr_t addr;
> +	size_t mapped = 0;
> +	__be64 *mtt;
> +	int i, err;
>  
> -	return mlx5_core_create_mkey(mdev, mkey, mkey_in, inlen);
> +	WARN_ON_ONCE(dir == DMA_NONE);
> +
> +	mtt = (__be64 *)MLX5_ADDR_OF(create_mkey_in, mkey_in, klm_pas_mtt);
> +
> +	if (dma_iova_try_alloc(mdev->device, state, 0, npages * PAGE_SIZE)) {
> +		addr = state->addr;
> +		for (i = 0; i < npages; i++) {
> +			err = dma_iova_link(mdev->device, state,
> +					    page_to_phys(page_list[i]), mapped,
> +					    PAGE_SIZE, dir, 0);
> +			if (err)
> +				goto error;
> +			*mtt++ = cpu_to_be64(addr);
> +			addr += PAGE_SIZE;
> +			mapped += PAGE_SIZE;
> +		}

This is an area I'd like to see improvement on as a follow up.

Given we know we are allocating contiguous IOVA we should be able to
request a certain alignment so we can know that it can be put into the
mkey as single mtt. That would eliminate the double translation cost in
the HW.

The RDMA mkey builder is able to do this from the scatterlist but the
logic to do that was too complex to copy into vfio. This is close to
being simple enough, just the alignment is the only problem.

Jason