From: will.deacon@arm•com (Will Deacon)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH 3/5] iommu/arm-smmu-v3: add IOMMU_CAP_BYPASS to the ARM SMMUv3 driver
Date: Wed, 19 Jul 2017 12:25:24 +0100 [thread overview]
Message-ID: <20170719112524.GF13642@arm.com> (raw)
In-Reply-To: <CAALAos8y0kLGrbwgz3u=ZVyteSicuPyQZ3Yp=LPZohXzVaE5NQ@mail.gmail.com>
On Wed, Jul 19, 2017 at 04:53:04PM +0530, Anup Patel wrote:
> On Wed, Jul 19, 2017 at 4:30 PM, Robin Murphy <robin.murphy@arm•com> wrote:
> > On 19/07/17 10:33, Anup Patel wrote:
> >> The ARM SMMUv3 support bypassing transactions for which domain
> >> is not configured. The patch adds corresponding IOMMU capability
> >> to advertise this fact.
> >>
> >> Signed-off-by: Anup Patel <anup.patel@broadcom•com>
> >> ---
> >> drivers/iommu/arm-smmu-v3.c | 2 ++
> >> 1 file changed, 2 insertions(+)
> >>
> >> diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c
> >> index 568c400..a6c7f66 100644
> >> --- a/drivers/iommu/arm-smmu-v3.c
> >> +++ b/drivers/iommu/arm-smmu-v3.c
> >> @@ -1423,6 +1423,8 @@ static bool arm_smmu_capable(enum iommu_cap cap)
> >> return true;
> >> case IOMMU_CAP_NOEXEC:
> >> return true;
> >> + case IOMMU_CAP_BYPASS:
> >> + return true;
> >
> > And this is never true. If Linux knows a device masters through the
> > SMMU, it will always have a default domain of some sort (either identity
> > or DMA ops). If Linux doesn't know, then it won't have been able to
> > initialise the stream table for the relevant stream IDs, thus any
> > 'bypass' DMA is going to raise C_BAD_STE. SMMUv3 can effectively only
> > bypass unknown stream IDs if disabled entirely.
>
> What if we don't want to use IOMMU for certain device and
> due to this we never provide "iommus" DT attribute in the
> device DT node. Further, we want to access device without
> "iommus" DT attribute from user-space using VFIO no-IOMMU.
Wait, you want to pass a device through to userspace but you don't want to
use the IOMMU? Why not?
If you describe the SMMU in firmware with only a partial topology
description, then you will run into problems with unknown masters trying to
perform DMA. That's the IOMMU doing its job!
Will
next prev parent reply other threads:[~2017-07-19 11:25 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-07-19 9:33 [PATCH 0/5] FlexRM support in VFIO platform Anup Patel
2017-07-19 9:33 ` [PATCH 1/5] iommu: Add capability IOMMU_CAP_BYPASS Anup Patel
2017-07-19 10:58 ` Robin Murphy
2017-07-19 11:19 ` Anup Patel
2017-07-19 11:23 ` Will Deacon
2017-07-19 11:26 ` Anup Patel
2017-07-19 11:29 ` Robin Murphy
2017-07-19 11:30 ` Will Deacon
2017-07-19 11:33 ` Anup Patel
2017-07-19 9:33 ` [PATCH 2/5] iommu/arm-smmu: add IOMMU_CAP_BYPASS to the ARM SMMU driver Anup Patel
2017-07-19 10:59 ` Robin Murphy
2017-07-19 9:33 ` [PATCH 3/5] iommu/arm-smmu-v3: add IOMMU_CAP_BYPASS to the ARM SMMUv3 driver Anup Patel
2017-07-19 11:00 ` Robin Murphy
2017-07-19 11:23 ` Anup Patel
2017-07-19 11:25 ` Will Deacon [this message]
2017-07-19 11:31 ` Anup Patel
2017-07-19 11:33 ` Will Deacon
2017-07-19 11:39 ` Anup Patel
2017-07-19 11:53 ` Will Deacon
2017-07-20 4:02 ` Anup Patel
2017-07-20 9:10 ` Will Deacon
2017-07-20 11:08 ` Anup Patel
2017-07-20 11:17 ` Will Deacon
2017-07-20 11:17 ` Robin Murphy
2017-07-24 17:16 ` Alex Williamson
2017-07-24 17:23 ` Robin Murphy
2017-07-24 19:06 ` Alex Williamson
2017-07-25 8:59 ` Anup Patel
2017-07-19 9:33 ` [PATCH 4/5] vfio: Allow No-IOMMU mode for IOMMUs with bypass capability Anup Patel
2017-07-19 9:33 ` [PATCH 5/5] vfio: platform: reset: Add Broadcom FlexRM reset module Anup Patel
2017-07-19 16:50 ` Scott Branden
2017-07-20 4:05 ` Anup Patel
2017-07-19 10:57 ` [PATCH 0/5] FlexRM support in VFIO platform Robin Murphy
2017-07-19 11:17 ` Anup Patel
2017-07-19 11:25 ` Robin Murphy
2017-07-19 11:28 ` Anup Patel
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20170719112524.GF13642@arm.com \
--to=will.deacon@arm$(echo .)com \
--cc=linux-arm-kernel@lists$(echo .)infradead.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox