linux-kernel - Re: [PATCH v2] dma-contiguous: define proper name for global cma region

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Message-ID: <20230801171838.GA14599@lst.de>
Date:   Tue, 1 Aug 2023 19:18:38 +0200
From:   Christoph Hellwig <hch@....de>
To:     Pintu Agarwal <pintu.ping@...il.com>
Cc:     Christoph Hellwig <hch@....de>,
        Pintu Kumar <quic_pintu@...cinc.com>,
        linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
        linux-mm@...ck.org, m.szyprowski@...sung.com, robin.murphy@....com,
        iommu@...ts.linux.dev, Sumit Semwal <sumit.semwal@...aro.org>,
        Benjamin Gaignard <benjamin.gaignard@...labora.com>,
        Liam Mark <lmark@...eaurora.org>,
        Laura Abbott <labbott@...hat.com>,
        Brian Starkey <Brian.Starkey@....com>,
        John Stultz <jstultz@...gle.com>,
        Christian König <christian.koenig@....com>,
        linux-media@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linaro-mm-sig@...ts.linaro.org
Subject: Re: [PATCH v2] dma-contiguous: define proper name for global cma
 region

On Tue, Aug 01, 2023 at 10:42:42PM +0530, Pintu Agarwal wrote:
> > I agree that reserved is not a very useful name.  Unfortuately the
> > name of the region leaks to userspace through cma_heap.
> >
> > So I think we need prep patches to hardcode "reserved" in
> > add_default_cma_heap first, and then remove the cma_get_name
> > first.
> 
> Sorry, but I could not fully understand your comments.
> Can you please elaborate a little more what changes are required in
> cma_heap if we change "reserved" to "global-cma-region" ?

Step 1:

Instead of setting exp_info.name to cma_get_name(cma);
in __add_cma_heap just set it to "reserved", probably by passing a name
argument.  You can also remove the unused data argument to __add_cma_heap
and/or just fold that function into the only caller while you're at it.

Step 2:

Remove cma_get_name, as it is unused now.

Step 3:

The patch your previously sent.

> You mean to say there are userspace tools that rely on this "reserved"
> naming for global cma ?

Yes.