From: Robin Murphy <robin.murphy@arm.com>
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Jason Gunthorpe <jgg@nvidia.com>
Cc: Lu Baolu <baolu.lu@linux.intel.com>,
Christoph Hellwig <hch@infradead.org>,
Joerg Roedel <joro@8bytes.org>,
Alex Williamson <alex.williamson@redhat.com>,
Bjorn Helgaas <bhelgaas@google.com>,
Kevin Tian <kevin.tian@intel.com>,
Ashok Raj <ashok.raj@intel.com>,
kvm@vger.kernel.org, rafael@kernel.org,
David Airlie <airlied@linux.ie>,
linux-pci@vger.kernel.org,
Thierry Reding <thierry.reding@gmail.com>,
Diana Craciun <diana.craciun@oss.nxp.com>,
Dmitry Osipenko <digetx@gmail.com>, Will Deacon <will@kernel.org>,
Stuart Yoder <stuyoder@gmail.com>,
Jonathan Hunter <jonathanh@nvidia.com>,
Chaitanya Kulkarni <kch@nvidia.com>,
Dan Williams <dan.j.williams@intel.com>,
Cornelia Huck <cohuck@redhat.com>,
linux-kernel@vger.kernel.org, Li Yang <leoyang.li@nxp.com>,
iommu@lists.linux-foundation.org,
Jacob jun Pan <jacob.jun.pan@intel.com>,
Daniel Vetter <daniel@ffwll.ch>
Subject: Re: [PATCH v6 02/11] driver core: Add dma_cleanup callback in bus_type
Date: Wed, 23 Feb 2022 17:05:23 +0000 [thread overview]
Message-ID: <78d2dd11-db30-39c8-6df4-d20f0dfbfce2@arm.com> (raw)
In-Reply-To: <YhZa3D5Xwv5oZm7L@kroah.com>
On 2022-02-23 16:03, Greg Kroah-Hartman wrote:
> On Wed, Feb 23, 2022 at 10:30:11AM -0400, Jason Gunthorpe wrote:
>> On Wed, Feb 23, 2022 at 10:09:01AM -0400, Jason Gunthorpe wrote:
>>> On Wed, Feb 23, 2022 at 03:06:35PM +0100, Greg Kroah-Hartman wrote:
>>>> On Wed, Feb 23, 2022 at 09:46:27AM -0400, Jason Gunthorpe wrote:
>>>>> On Wed, Feb 23, 2022 at 01:04:00PM +0000, Robin Murphy wrote:
>>>>>
>>>>>> 1 - tmp->driver is non-NULL because tmp is already bound.
>>>>>> 1.a - If tmp->driver->driver_managed_dma == 0, the group must currently be
>>>>>> DMA-API-owned as a whole. Regardless of what driver dev has unbound from,
>>>>>> its removal does not release someone else's DMA API (co-)ownership.
>>>>>
>>>>> This is an uncommon locking pattern, but it does work. It relies on
>>>>> the mutex being an effective synchronization barrier for an unlocked
>>>>> store:
>>>>>
>>>>> WRITE_ONCE(dev->driver, NULL)
>>>>
>>>> Only the driver core should be messing with the dev->driver pointer as
>>>> when it does so, it already has the proper locks held. Do I need to
>>>> move that to a "private" location so that nothing outside of the driver
>>>> core can mess with it?
>>>
>>> It would be nice, I've seen a abuse and mislocking of it in drivers
>>
>> Though to be clear, what Robin is describing is still keeping the
>> dev->driver stores in dd.c, just reading it in a lockless way from
>> other modules.
>
> "other modules" should never care if a device has a driver bound to it
> because instantly after the check happens, it can change so what ever
> logic it wanted to do with that knowledge is gone.
>
> Unless the bus lock is held that the device is on, but that should be
> only accessable from within the driver core as it controls that type of
> stuff, not any random other part of the kernel.
>
> And in looking at this, ick, there are loads of places in the kernel
> that are thinking that this pointer being set to something actually
> means something. Sometimes it does, but lots of places, it doesn't as
> it can change.
That's fine. In this case we're only talking about the low-level IOMMU
code which has to be in cahoots with the driver core to some degree (via
these new callbacks) anyway, but if you're uncomfortable about relying
on dev->driver even there, I can live with that. There are several
potential places to capture the relevant information in IOMMU API
private data, from the point in really_probe() where it *is* stable, and
then never look at dev->driver ever again - even from .dma_cleanup() or
future equivalent, which is the aspect from whence this whole
proof-of-concept tangent span out.
Cheers,
Robin.
next prev parent reply other threads:[~2022-02-23 17:05 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-02-18 0:55 [PATCH v6 00/11] Fix BUG_ON in vfio_iommu_group_notifier() Lu Baolu
2022-02-18 0:55 ` [PATCH v6 01/11] iommu: Add dma ownership management interfaces Lu Baolu
2022-02-19 7:31 ` Christoph Hellwig
2022-02-21 4:02 ` Lu Baolu
2022-02-23 18:00 ` Robin Murphy
2022-02-23 18:02 ` Jason Gunthorpe
2022-02-23 18:20 ` Robin Murphy
2022-02-23 18:32 ` Jason Gunthorpe
2022-02-24 5:16 ` Lu Baolu
2022-02-24 5:29 ` Lu Baolu
2022-02-24 8:58 ` Robin Murphy
2022-02-24 5:21 ` Lu Baolu
2022-02-18 0:55 ` [PATCH v6 02/11] driver core: Add dma_cleanup callback in bus_type Lu Baolu
2022-02-19 7:32 ` Christoph Hellwig
2022-02-21 20:43 ` Robin Murphy
2022-02-21 23:48 ` Jason Gunthorpe
2022-02-22 4:48 ` Lu Baolu
2022-02-22 10:58 ` Robin Murphy
2022-02-22 15:16 ` Jason Gunthorpe
2022-02-22 21:18 ` Robin Murphy
2022-02-22 23:53 ` Jason Gunthorpe
2022-02-23 5:01 ` Lu Baolu
2022-02-23 13:04 ` Robin Murphy
2022-02-23 13:46 ` Jason Gunthorpe
2022-02-23 14:06 ` Greg Kroah-Hartman
2022-02-23 14:09 ` Jason Gunthorpe
2022-02-23 14:30 ` Jason Gunthorpe
2022-02-23 16:03 ` Greg Kroah-Hartman
2022-02-23 17:05 ` Robin Murphy [this message]
2022-02-23 17:47 ` Greg Kroah-Hartman
2022-02-18 0:55 ` [PATCH v6 03/11] amba: Stop sharing platform_dma_configure() Lu Baolu
2022-02-18 0:55 ` [PATCH v6 04/11] bus: platform,amba,fsl-mc,PCI: Add device DMA ownership management Lu Baolu
2022-02-18 7:55 ` Greg Kroah-Hartman
2022-02-18 0:55 ` [PATCH v6 05/11] PCI: pci_stub: Set driver_managed_dma Lu Baolu
2022-02-18 0:55 ` [PATCH v6 06/11] PCI: portdrv: " Lu Baolu
2022-02-18 0:55 ` [PATCH v6 07/11] vfio: Set DMA ownership for VFIO devices Lu Baolu
2022-02-18 0:55 ` [PATCH v6 08/11] vfio: Remove use of vfio_group_viable() Lu Baolu
2022-02-18 0:55 ` [PATCH v6 09/11] vfio: Delete the unbound_list Lu Baolu
2022-02-18 0:55 ` [PATCH v6 10/11] vfio: Remove iommu group notifier Lu Baolu
2022-02-23 21:53 ` Alex Williamson
2022-02-24 2:49 ` Lu Baolu
2022-02-18 0:55 ` [PATCH v6 11/11] iommu: Remove iommu group changes notifier Lu Baolu
2022-02-18 15:51 ` [PATCH v6 00/11] Fix BUG_ON in vfio_iommu_group_notifier() Jason Gunthorpe
2022-02-21 3:38 ` Lu Baolu
2022-02-28 0:58 ` Lu Baolu
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