Re: [PATCH 2/7] RDMA/hfi1: don't pass bogus GFP_ flags to dma_alloc_coherent

From: Dean Luick <dean.luick@cornelisnetworks.com>
To: Christoph Hellwig <hch@lst.de>, Robin Murphy <robin.murphy@arm.com>
Cc: Dennis Dalessandro <dennis.dalessandro@cornelisnetworks.com>,
	Mauro Carvalho Chehab <mchehab@kernel.org>,
	Alexandra Winter <wintera@linux.ibm.com>,
	Wenjia Zhang <wenjia@linux.ibm.com>,
	Marek Szyprowski <m.szyprowski@samsung.com>,
	Jaroslav Kysela <perex@perex.cz>, Takashi Iwai <tiwai@suse.com>,
	Russell King <linux@armlinux.org.uk>,
	linux-arm-kernel@lists.infradead.org, linux-rdma@vger.kernel.org,
	iommu@lists.linux.dev, linux-media@vger.kernel.org,
	netdev@vger.kernel.org, linux-s390@vger.kernel.org,
	alsa-devel@alsa-project.org
Subject: Re: [PATCH 2/7] RDMA/hfi1: don't pass bogus GFP_ flags to dma_alloc_coherent
Date: Wed, 16 Nov 2022 11:49:21 -0600	[thread overview]
Message-ID: <2c60c692-58d7-d06d-826e-ea49bb1eca13@cornelisnetworks.com> (raw)
In-Reply-To: <20221116154507.GB18491@lst.de>

On 11/16/2022 9:45 AM, Christoph Hellwig wrote:
> On Wed, Nov 16, 2022 at 03:15:10PM +0000, Robin Murphy wrote:
>> Coherent DMA buffers are allocated by a kernel driver or subsystem for the
>> use of a device managed by that driver or subsystem, and thus they
>> fundamentally belong to the kernel as proxy for the device. Any coherent
>> DMA buffer may be mapped to userspace with the dma_mmap_*() interfaces, but
>> they're never a "userspace allocation" in that sense.
>
> Exactly.  I could not find a place to map the buffers to userspace,
> so if it does that without using the proper interfaces we need to fix
> that as well.  Dean, can you point me to the mmap code?

See hfi1_file_mmap(), cases RCV_HDRQ and RCV_EGRBUF, for the two items you changed in hfi1.  Both directly use remap_pfn_range(), which is probably the original approved call, but now is now buried deep within dma_mmap_*().  As you say - these should be updated.  That said, the eager buffer mapping will stitch together multiple eager buffers into a single user map/vma.  I don't see how to do that with the dma_mmap_*() interface.

-Dean
External recipient