linux-kernel - Re: [PATCH v6 4/5] dma-buf: heaps: Add CMA heap to dmabuf heaps

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]

Date:   Thu, 25 Jul 2019 10:10:08 -0400
From:   "Andrew F. Davis" <afd@...com>
To:     Christoph Hellwig <hch@...radead.org>
CC:     John Stultz <john.stultz@...aro.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Laura Abbott <labbott@...hat.com>,
        Benjamin Gaignard <benjamin.gaignard@...aro.org>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Liam Mark <lmark@...eaurora.org>,
        Pratik Patel <pratikp@...eaurora.org>,
        Brian Starkey <Brian.Starkey@....com>,
        Vincent Donnefort <Vincent.Donnefort@....com>,
        Sudipto Paul <Sudipto.Paul@....com>,
        Xu YiPing <xuyiping@...ilicon.com>,
        "Chenfeng (puck)" <puck.chen@...ilicon.com>,
        butao <butao@...ilicon.com>,
        "Xiaqing (A)" <saberlily.xia@...ilicon.com>,
        Yudongbin <yudongbin@...ilicon.com>,
        Chenbo Feng <fengc@...gle.com>,
        Alistair Strachan <astrachan@...gle.com>,
        dri-devel <dri-devel@...ts.freedesktop.org>
Subject: Re: [PATCH v6 4/5] dma-buf: heaps: Add CMA heap to dmabuf heaps

On 7/25/19 10:04 AM, Christoph Hellwig wrote:
> On Thu, Jul 25, 2019 at 09:31:50AM -0400, Andrew F. Davis wrote:
>> But that's just it, dma-buf does not assume buffers are backed by normal
>> kernel managed memory, it is up to the buffer exporter where and when to
>> allocate the memory. The memory backed by this SRAM buffer does not have
>> the normal struct page backing. So moving the map, sync, etc functions
>> to common code would fail for this and many other heap types. This was a
>> major problem with Ion that prompted this new design.
> 
> The code clearly shows it has page backing, e.g. this:
> 
> +	sg_set_page(table->sgl, pfn_to_page(PFN_DOWN(buffer->paddr)), buffer->len, 0);
> 
> and the fact that it (and the dma-buf API) uses scatterlists, which 
> requires pages.
> 

Pages yes, but not "normal" pages from the kernel managed area.
page_to_pfn() will return bad values on the pages returned by this
allocator and so will any of the kernel sync/map functions. Therefor
those operations cannot be common and need special per-heap handling.

Andrew