linux-kernel - Re: [PATCH 5/9] PCI: host: brcmstb: add dma-ranges for inbound traffic

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]

Message-ID: <CANCKTBtxp9gSdndKAZ7xGA+VozQsn2PX_-9P8A22_5Matbb7-w@mail.gmail.com>
Date:   Fri, 20 Oct 2017 11:27:41 -0400
From:   Jim Quinlan <jim2101024@...il.com>
To:     Christoph Hellwig <hch@....de>
Cc:     Robin Murphy <robin.murphy@....com>, linux-kernel@...r.kernel.org,
        Mark Rutland <mark.rutland@....com>,
        Linux-MIPS <linux-mips@...ux-mips.org>,
        Florian Fainelli <f.fainelli@...il.com>,
        devicetree@...r.kernel.org, linux-pci <linux-pci@...r.kernel.org>,
        Kevin Cernekee <cernekee@...il.com>,
        Will Deacon <will.deacon@....com>,
        Ralf Baechle <ralf@...ux-mips.org>,
        Rob Herring <robh+dt@...nel.org>,
        bcm-kernel-feedback-list <bcm-kernel-feedback-list@...adcom.com>,
        Gregory Fong <gregory.0xf0@...il.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Brian Norris <computersforpeace@...il.com>,
        linux-arm-kernel@...ts.infradead.org,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        iommu@...ts.linux-foundation.org
Subject: Re: [PATCH 5/9] PCI: host: brcmstb: add dma-ranges for inbound traffic

On Fri, Oct 20, 2017 at 10:57 AM, Christoph Hellwig <hch@....de> wrote:
> On Fri, Oct 20, 2017 at 10:41:56AM -0400, Jim Quinlan wrote:
>> I am not sure I understand your comment -- the size of the request
>> shouldn't be a factor.  Let's look at your example of the DMA request
>> of 3fffff00 to 4000000f (physical memory).  Lets say it is for 15
>> pages.  If we block out  the last page [0x3ffff000..0x3fffffff] from
>> what is available, there is no 15 page span that can happen across the
>> 0x40000000 boundary.  For SG, there can be no merge that connects a
>> page from one region to another region.  Can you give an example of
>> the scenario you are thinking of?
>
> What prevents a merge from say the regions of
> 0....3fffffff and 40000000....7fffffff?

Huh? [0x3ffff000...x3ffffff] is not available to be used. Drawing from
the original example, we now have to tell Linux that these are now our
effective memory regions:

      memc0-a@[        0....3fffefff] <=> pci@[        0....3fffefff]
      memc0-b@[100000000...13fffefff] <=> pci@[ 40000000....7fffefff]
      memc1-a@[ 40000000....7fffefff] <=> pci@[ 80000000....bfffefff]
      memc1-b@[300000000...33fffefff] <=> pci@[ c0000000....ffffefff]
      memc2-a@[ 80000000....bfffefff] <=> pci@[100000000...13fffefff]
      memc2-b@[c00000000...c3fffffff] <=> pci@[140000000...17fffffff]

This leaves a one-page gap between phsyical memory regions which would
normally be contiguous. One cannot have a dma alloc that spans any two
regions.  This is a drastic step, but I don't see an alternative.
Perhaps  I may be missing what you are saying...