From: Stefano Stabellini <sstabellini@kernel.org>
To: Julien Grall <julien@xen.org>
Cc: Stefano Stabellini <sstabellini@kernel.org>,
Rahul Singh <Rahul.Singh@arm.com>,
xen-devel <xen-devel@lists.xenproject.org>,
Bertrand Marquis <Bertrand.Marquis@arm.com>,
"Volodymyr_Babchuk@epam.com" <Volodymyr_Babchuk@epam.com>,
"brian.woods@xilinx.com" <brian.woods@xilinx.com>
Subject: Re: [PATCH v3 0/3] Generic SMMU Bindings
Date: Tue, 2 Feb 2021 10:27:18 -0800 (PST) [thread overview]
Message-ID: <alpine.DEB.2.21.2102021024100.29047@sstabellini-ThinkPad-T480s> (raw)
In-Reply-To: <7ddc6e1b-41ce-37ae-f86e-39893f53a0ec@xen.org>
On Tue, 2 Feb 2021, Julien Grall wrote:
> On 02/02/2021 17:44, Stefano Stabellini wrote:
> > On Tue, 2 Feb 2021, Rahul Singh wrote:
> > > Hello Stefano,
> > >
> > > > On 26 Jan 2021, at 10:58 pm, Stefano Stabellini <sstabellini@kernel.org>
> > > > wrote:
> > > >
> > > > Hi all,
> > > >
> > > > This series introduces support for the generic SMMU bindings to
> > > > xen/drivers/passthrough/arm/smmu.c.
> > > >
> > > > The last version of the series was
> > > > https://marc.info/?l=xen-devel&m=159539053406643
> > > >
> > > > I realize that it is late for 4.15 -- I think it is OK if this series
> > > > goes in afterwards.
> > >
> > > I tested the series on the Juno board it is woking fine.
> > > I found one issue in SMMU driver while testing this series that is not
> > > related to this series but already existing issue in SMMU driver.
> > >
> > > If there are more than one device behind SMMU and they share the same
> > > Stream-Id, SMMU driver is creating the new SMR entry without checking the
> > > already configured SMR entry if SMR entry correspond to stream-id is
> > > already configured. Because of this I observed the stream match conflicts
> > > on Juno board.
> > >
> > > (XEN) smmu: /iommu@7fb30000: Unexpected global fault, this could be
> > > serious
> > > (XEN) smmu: /iommu@7fb30000: GFSR 0x00000004, GFSYNR0 0x00000006,
> > > GFSYNR1 0x00000000, GFSYNR2 0x00000000
> > >
> > >
> > > Below two patches is required to be ported to Xen to fix the issue from
> > > Linux driver.
> > >
> > > https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/drivers/iommu/arm-smmu.c?h=linux-5.8.y&id=1f3d5ca43019bff1105838712d55be087d93c0da
> > > https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/drivers/iommu/arm-smmu.c?h=linux-5.8.y&id=21174240e4f4439bb8ed6c116cdbdc03eba2126e
> >
> >
> > Good catch and thanks for the pointers! Do you have any interest in
> > backporting these two patches or should I put them on my TODO list?
> >
> > Unrelated to who does the job, we should discuss if it makes sense to
> > try to fix the bug for 4.15. The patches don't seem trivial so I am
> > tempted to say that it might be best to leave the bug unfixed for 4.15
> > and fix it later.
>
> SMMU support on Juno is not that interesting because IIRC the stream-ID is the
> same for all the devices. So it is all or nothing passthrough.
>
> For other HW, this may be a useful feature. Yet we would need a way to group
> the devices for passthrough.
>
> In this context, I would consider it more a feature than a bug because the
> SMMU driver never remotely work on such HW.
I see. To be honest I wasn't thinking of Juno (I wasn't aware of its
limitations) but of potential genuine situations where stream-ids are
the same for 2 devices. I know it can happen with PCI devices for
instance, although I am aware we don't have PCI passthrough yet. I don't
know if it is possible for it to happen with non-PCI devices but I
wouldn't be surprised if it can.
next prev parent reply other threads:[~2021-02-02 18:27 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-26 22:58 [PATCH v3 0/3] Generic SMMU Bindings Stefano Stabellini
2021-01-26 22:58 ` [PATCH v3 1/3] arm,smmu: switch to using iommu_fwspec functions Stefano Stabellini
2021-02-02 16:07 ` Rahul Singh
2021-01-26 22:58 ` [PATCH v3 2/3] arm,smmu: restructure code in preparation to new bindings support Stefano Stabellini
2021-02-02 16:09 ` Rahul Singh
2021-01-26 22:58 ` [PATCH v3 3/3] arm,smmu: add support for generic DT bindings. Implement add_device and dt_xlate Stefano Stabellini
2021-02-02 16:09 ` Rahul Singh
2021-02-02 16:07 ` [PATCH v3 0/3] Generic SMMU Bindings Rahul Singh
2021-02-02 17:44 ` Stefano Stabellini
2021-02-02 17:50 ` Julien Grall
2021-02-02 18:27 ` Stefano Stabellini [this message]
2021-02-02 18:43 ` Julien Grall
2021-02-03 17:14 ` Rahul Singh
2021-04-05 15:23 ` Julien Grall
2021-04-06 23:59 ` Stefano Stabellini
2021-04-07 15:43 ` Rahul Singh
2021-04-10 0:27 ` Stefano Stabellini
2021-04-12 10:20 ` Rahul Singh
2021-04-13 0:27 ` Stefano Stabellini
2021-04-14 10:42 ` Rahul Singh
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