netdev - Re: [PATCH 2/2] cnic,bnx2,bnx2x: use UIO_MEM_DMA

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Message-ID: <2024013125-unraveled-definite-7fc6@gregkh>
Date: Wed, 31 Jan 2024 13:29:56 -0800
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: Chris Leech <cleech@...hat.com>
Cc: Nilesh Javali <njavali@...vell.com>, Christoph Hellwig <hch@....de>,
	John Meneghini <jmeneghi@...hat.com>, Lee Duncan <lduncan@...e.com>,
	Mike Christie <michael.christie@...cle.com>,
	Hannes Reinecke <hare@...nel.org>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-scsi@...r.kernel.org,
	GR-QLogic-Storage-Upstream@...vell.com
Subject: Re: [PATCH 2/2] cnic,bnx2,bnx2x: use UIO_MEM_DMA_COHERENT

On Wed, Jan 31, 2024 at 11:17:32AM -0800, Chris Leech wrote:
> Use the UIO_MEM_DMA_COHERENT type to properly handle mmap for
> dma_alloc_coherent buffers.
> 
> The cnic l2_ring and l2_buf mmaps have caused page refcount issues as
> the dma_alloc_coherent no longer provide __GFP_COMP allocation as per
> commit "dma-mapping: reject __GFP_COMP in dma_alloc_attrs".
> 
> Fix this by having the uio device use dma_mmap_coherent.
> 
> The bnx2 and bnx2x status block allocations are also dma_alloc_coherent,
> and should use dma_mmap_coherent. They don't allocate multiple pages,
> but this interface does not work correctly with an iommu enabled unless
> dma_mmap_coherent is used.
> 
> Fixes: bb73955c0b1d ("cnic: don't pass bogus GFP_ flags to dma_alloc_coherent")

This is really the commit that broke things?  By adding this, are you
expecting anyone to backport this change to older kernels?

thanks,

greg k-h