From: Arnd Bergmann <arnd@arndb.de>
To: Grant Grundler <grundler@chromium.org>
Cc: "linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>,
Thierry Reding <thierry.reding@gmail.com>,
Mark Rutland <mark.rutland@arm.com>,
Linux DeviceTree <devicetree@vger.kernel.org>,
linux-samsung-soc <linux-samsung-soc@vger.kernel.org>,
Pawel Moll <pawel.moll@arm.com>,
Ian Campbell <ijc+devicetree@hellion.org.uk>,
Joerg Roedel <joro@8bytes.org>,
Stephen Warren <swarren@wwwdotorg.org>,
Will Deacon <will.deacon@arm.com>,
LKML <linux-kernel@vger.kernel.org>,
Marc Zyngier <marc.zyngier@arm.com>,
Linux IOMMU <iommu@lists.linux-foundation.org>,
Rob Herring <robh+dt@kernel.org>,
Kumar Gala <galak@codeaurora.org>,
linux-tegra@vger.kernel.org, Cho KyongHo <pullip.cho@samsung.com>,
Dave Martin <Dave.Martin@arm.com>
Subject: Re: [PATCH] devicetree: Add generic IOMMU device tree bindings
Date: Wed, 21 May 2014 18:01:06 +0200 [thread overview]
Message-ID: <4376848.aihqtRyYDl@wuerfel> (raw)
In-Reply-To: <CANEJEGvhEsC9wKqX_pYmOg7LwsQkoN9=jjXJuW0UeEa9XywSPw@mail.gmail.com>
On Wednesday 21 May 2014 08:44:42 Grant Grundler wrote:
> On Wed, May 21, 2014 at 2:32 AM, Arnd Bergmann <arnd@arndb.de> wrote:
> > On Wednesday 21 May 2014 11:02:45 Thierry Reding wrote:
> >> On Wed, May 21, 2014 at 10:54:42AM +0200, Arnd Bergmann wrote:
> >>
> >> > Right. As long as we always unmap the buffers from the IOMMU after they
> >> > have stopped being in use, it's very unlikely that even a broken device
> >> > driver causes a DMA into some bus address that happens to be mapped for
> >> > another device.
> >>
> >> I think that if buffers remain mapped in the IOMMU when they have been
> >> deallocated that should be considered a bug.
>
> There is currently no general requirement to tear down mappings immediately.
> An option to enforce immediate tear down might be useful since I agree
> Virtual Guests sharing host memory through shared physical devices
> will want that. ie there should be no opportunity for a shared device
> to be able to access another guests memory through "stale" (but live)
> DMA mappings. I don't think that's the case but I'd ask someone like
> Alex Williamson for a more certain answer.
I believe powerpc has a boot-time option to enforce the immediate
IOTLB flush, which is very useful for device driver debugging when
something goes wrong with stale DMAs.
> > Obviously you have to maintain the IO page tables correctly.
>
> To be clear, "Correctly" in this case just means until the IOTLB is
> flushed, the given IOMMU Pdir entries are marked "in use" even though
> the driver has handed "ownership" back to the IOMMU driver.
I don't know what a Pdir is, but I guess strictly speaking we have
to ensure that all IO page table entries that have been unmapped by
a driver are marked as invalid at least by the time the IOTLB is flushed,
plus we have to flush each entry before it gets reused for a different
page.
Arnd
next prev parent reply other threads:[~2014-05-21 16:01 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-05-16 12:23 Thierry Reding
2014-05-17 8:04 ` Cho KyongHo
2014-05-17 20:48 ` Thierry Reding
2014-05-19 10:26 ` Arnd Bergmann
2014-05-19 12:53 ` Thierry Reding
2014-05-19 17:22 ` Dave Martin
2014-05-19 20:32 ` Thierry Reding
2014-05-20 10:08 ` Arnd Bergmann
2014-05-20 13:07 ` Dave Martin
2014-05-20 13:23 ` Arnd Bergmann
2014-05-20 15:26 ` Will Deacon
2014-05-20 16:39 ` Dave Martin
2014-05-20 20:40 ` Arnd Bergmann
2014-05-19 18:34 ` Arnd Bergmann
2014-05-19 20:59 ` Thierry Reding
2014-05-20 10:04 ` Arnd Bergmann
2014-05-20 11:05 ` Thierry Reding
2014-05-20 11:15 ` Arnd Bergmann
2014-05-20 12:02 ` Thierry Reding
2014-05-20 12:41 ` Arnd Bergmann
2014-05-20 13:17 ` Thierry Reding
2014-05-20 13:34 ` Arnd Bergmann
2014-05-20 14:00 ` Thierry Reding
2014-05-20 20:31 ` Arnd Bergmann
2014-05-21 8:16 ` Thierry Reding
2014-05-21 8:54 ` Arnd Bergmann
2014-05-21 9:02 ` Thierry Reding
2014-05-21 9:32 ` Arnd Bergmann
2014-05-21 15:44 ` Grant Grundler
2014-05-21 16:01 ` Arnd Bergmann [this message]
2014-05-20 15:24 ` Dave Martin
2014-05-20 20:26 ` Arnd Bergmann
2014-05-21 8:26 ` Thierry Reding
2014-05-21 8:50 ` Arnd Bergmann
2014-05-21 9:00 ` Thierry Reding
2014-05-21 9:36 ` Arnd Bergmann
2014-05-21 10:50 ` Thierry Reding
2014-05-21 14:01 ` Arnd Bergmann
2014-05-21 17:09 ` Dave Martin
2014-05-21 18:11 ` Arnd Bergmann
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