linux-kernel - Re: [PATCH v4 6/7] iommu/dma: Centralise iommu_setup_dma

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Date: Tue, 30 Apr 2024 13:56:07 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Robin Murphy <robin.murphy@....com>
Cc: Joerg Roedel <joro@...tes.org>, Christoph Hellwig <hch@....de>, Vineet Gupta <vgupta@...nel.org>, 
	Russell King <linux@...linux.org.uk>, Catalin Marinas <catalin.marinas@....com>, 
	Will Deacon <will@...nel.org>, Huacai Chen <chenhuacai@...nel.org>, WANG Xuerui <kernel@...0n.name>, 
	Thomas Bogendoerfer <tsbogend@...ha.franken.de>, Paul Walmsley <paul.walmsley@...ive.com>, 
	Palmer Dabbelt <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>, 
	Lorenzo Pieralisi <lpieralisi@...nel.org>, Hanjun Guo <guohanjun@...wei.com>, 
	Sudeep Holla <sudeep.holla@....com>, "K. Y. Srinivasan" <kys@...rosoft.com>, 
	Haiyang Zhang <haiyangz@...rosoft.com>, Wei Liu <wei.liu@...nel.org>, 
	Dexuan Cui <decui@...rosoft.com>, Suravee Suthikulpanit <suravee.suthikulpanit@....com>, 
	David Woodhouse <dwmw2@...radead.org>, Lu Baolu <baolu.lu@...ux.intel.com>, 
	Niklas Schnelle <schnelle@...ux.ibm.com>, Matthew Rosato <mjrosato@...ux.ibm.com>, 
	Gerald Schaefer <gerald.schaefer@...ux.ibm.com>, 
	Jean-Philippe Brucker <jean-philippe@...aro.org>, Rob Herring <robh+dt@...nel.org>, 
	Frank Rowand <frowand.list@...il.com>, Marek Szyprowski <m.szyprowski@...sung.com>, 
	Jason Gunthorpe <jgg@...pe.ca>, linux-kernel@...r.kernel.org, 
	linux-arm-kernel@...ts.infradead.org, linux-acpi@...r.kernel.org, 
	iommu@...ts.linux.dev, devicetree@...r.kernel.org, 
	Jason Gunthorpe <jgg@...dia.com>
Subject: Re: [PATCH v4 6/7] iommu/dma: Centralise iommu_setup_dma_ops()

On Tue, 30 Apr 2024 at 13:20, Robin Murphy <robin.murphy@....com> wrote:
>
> On 2024-04-30 1:41 am, Dmitry Baryshkov wrote:
> > On Tue, 30 Apr 2024 at 01:26, Robin Murphy <robin.murphy@....com> wrote:
> >>
> >> On 2024-04-29 5:31 pm, Dmitry Baryshkov wrote:
> >>> On Fri, Apr 19, 2024 at 05:54:45PM +0100, Robin Murphy wrote:
> >>>> It's somewhat hard to see, but arm64's arch_setup_dma_ops() should only
> >>>> ever call iommu_setup_dma_ops() after a successful iommu_probe_device(),
> >>>> which means there should be no harm in achieving the same order of
> >>>> operations by running it off the back of iommu_probe_device() itself.
> >>>> This then puts it in line with the x86 and s390 .probe_finalize bodges,
> >>>> letting us pull it all into the main flow properly. As a bonus this lets
> >>>> us fold in and de-scope the PCI workaround setup as well.
> >>>>
> >>>> At this point we can also then pull the call up inside the group mutex,
> >>>> and avoid having to think about whether iommu_group_store_type() could
> >>>> theoretically race and free the domain if iommu_setup_dma_ops() ran just
> >>>> *before* iommu_device_use_default_domain() claims it... Furthermore we
> >>>> replace one .probe_finalize call completely, since the only remaining
> >>>> implementations are now one which only needs to run once for the initial
> >>>> boot-time probe, and two which themselves render that path unreachable.
> >>>>
> >>>> This leaves us a big step closer to realistically being able to unpick
> >>>> the variety of different things that iommu_setup_dma_ops() has been
> >>>> muddling together, and further streamline iommu-dma into core API flows
> >>>> in future.
> >>>>
> >>>> Reviewed-by: Lu Baolu <baolu.lu@...ux.intel.com> # For Intel IOMMU
> >>>> Reviewed-by: Jason Gunthorpe <jgg@...dia.com>
> >>>> Tested-by: Hanjun Guo <guohanjun@...wei.com>
> >>>> Signed-off-by: Robin Murphy <robin.murphy@....com>
> >>>> ---
> >>>> v2: Shuffle around to make sure the iommu_group_do_probe_finalize() case
> >>>>       is covered as well, with bonus side-effects as above.
> >>>> v3: *Really* do that, remembering the other two probe_finalize sites too.
> >>>> ---
> >>>>    arch/arm64/mm/dma-mapping.c  |  2 --
> >>>>    drivers/iommu/amd/iommu.c    |  8 --------
> >>>>    drivers/iommu/dma-iommu.c    | 18 ++++++------------
> >>>>    drivers/iommu/dma-iommu.h    | 14 ++++++--------
> >>>>    drivers/iommu/intel/iommu.c  |  7 -------
> >>>>    drivers/iommu/iommu.c        | 20 +++++++-------------
> >>>>    drivers/iommu/s390-iommu.c   |  6 ------
> >>>>    drivers/iommu/virtio-iommu.c | 10 ----------
> >>>>    include/linux/iommu.h        |  7 -------
> >>>>    9 files changed, 19 insertions(+), 73 deletions(-)
> >>>
> >>> This patch breaks UFS on Qualcomm SC8180X Primus platform:
> >>>
> >>>
> >>> [    3.846856] arm-smmu 15000000.iommu: Unhandled context fault: fsr=0x402, iova=0x1032db3e0, fsynr=0x130000, cbfrsynra=0x300, cb=4
> >>
> >> Hmm, a context fault implies that the device did get attached to a DMA
> >> domain, thus has successfully been through __iommu_probe_device(), yet
> >> somehow still didn't get the right DMA ops (since that "IOVA" looks more
> >> like a PA to me). Do you see the "Adding to IOMMU group..." message for
> >> this device, and/or any other relevant messages or errors before this
> >> point?
> >
> > No, nothing relevant.
> >
> > [    8.372395] ufshcd-qcom 1d84000.ufshc: Adding to iommu group 6
> >
> > (please ignore the timestamp, it comes before ufshc being probed).
> >
> >> I'm guessing there's a fair chance probe deferral might be
> >> involved as well. I'd like to understand what path(s) this ends up
> >> taking through __iommu_probe_device() and of_dma_configure(), or at
> >> least the number and order of probe attempts between the UFS and SMMU
> >> drivers.
> >
> > __iommu_probe_device() gets called twice and returns early because ops is NULL.
> >
> > Then finally of_dma_configure_id() is called. The following branches are taken:
> >
> > np == dev->of_node
> > of_dma_get_range() returned 0
> > bus_dma_limit and dma_range_map are set
> > __iommu_probe_device() is called, using the `!group->default_domain &&
> > !group_lis` case, then group->default_domain() is not NULL,
> > In the end, iommu_setup_dma_ops() is called.
> >
> > Then the ufshc probe defers (most likely the PHY is not present or
> > some other device is not there yet).
>
> Ah good, probe deferral. And indeed the half-formed hunch from last
> night grew into a pretty definite idea by this morning... patch incoming.

Thanks a lot for the quick fix!


-- 
With best wishes
Dmitry