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

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Message-ID: <CAPnfmX+ZXraFC1+2Lu+WdgdUud4ALEcFAcsRQotVjfsGFsqUvw@mail.gmail.com>
Date: Wed, 31 Jan 2024 13:46:40 -0800
From: Chris Leech <cleech@...hat.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
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 1:30 PM Greg Kroah-Hartman
<gregkh@...uxfoundation.org> wrote:
>
> 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?

That's certainly where things stopped working altogether, iommu issues
go back further.

- Chris