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From: Nicolin Chen <nicolinc@nvidia.com>
To: Robin Murphy <robin.murphy@arm.com>
Cc: Yong Wu <yong.wu@mediatek.com>,
	"Tian, Kevin" <kevin.tian@intel.com>,
	Jason Gunthorpe <jgg@nvidia.com>,
	Baolu Lu <baolu.lu@linux.intel.com>,
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	"thierry.reding@gmail.com" <thierry.reding@gmail.com>,
	"will@kernel.org" <will@kernel.org>,
	"alyssa@rosenzweig.io" <alyssa@rosenzweig.io>,
	"jean-philippe@linaro.org" <jean-philippe@linaro.org>,
	"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
	"zhang.lyra@gmail.com" <zhang.lyra@gmail.com>,
	"iommu@lists.linux-foundation.org"
	<iommu@lists.linux-foundation.org>,
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	<linux-mediatek@lists.infradead.org>
Subject: Re: [PATCH v3 1/5] iommu: Return -EMEDIUMTYPE for incompatible domain and device/group
Date: Thu, 30 Jun 2022 08:47:40 -0700	[thread overview]
Message-ID: <Yr3FnN/BllcvsxsP@Asurada-Nvidia> (raw)
In-Reply-To: <e5799215-8b55-90a8-7ca4-35f85ffb5969@arm.com>

On Thu, Jun 30, 2022 at 09:21:42AM +0100, Robin Murphy wrote:
> External email: Use caution opening links or attachments
> 
> 
> On 2022-06-29 20:47, Nicolin Chen wrote:
> > On Fri, Jun 24, 2022 at 03:19:43PM -0300, Jason Gunthorpe wrote:
> > > On Fri, Jun 24, 2022 at 06:35:49PM +0800, Yong Wu wrote:
> > > 
> > > > > > It's not used in VFIO context. "return 0" just satisfy the iommu
> > > > > > framework to go ahead. and yes, here we only allow the shared
> > > > > > "mapping-domain" (All the devices share a domain created
> > > > > > internally).
> > > 
> > > What part of the iommu framework is trying to attach a domain and
> > > wants to see success when the domain was not actually attached ?
> > > 
> > > > > What prevent this driver from being used in VFIO context?
> > > > 
> > > > Nothing prevent this. Just I didn't test.
> > > 
> > > This is why it is wrong to return success here.
> > 
> > Hi Yong, would you or someone you know be able to confirm whether
> > this "return 0" is still a must or not?
> 
> From memory, it is unfortunately required, due to this driver being in
> the rare position of having to support multiple devices in a single
> address space on 32-bit ARM. Since the old ARM DMA code doesn't
> understand groups, the driver sets up its own canonical
> dma_iommu_mapping to act like a default domain, but then has to politely
> say "yeah OK" to arm_setup_iommu_dma_ops() for each device so that they
> do all end up with the right DMA ops rather than dying in screaming
> failure (the ARM code's per-device mappings then get leaked, but we
> can't really do any better).
> 
> The whole mess disappears in the proper default domain conversion, but
> in the meantime, it's still safe to assume that nobody's doing VFIO with
> embedded display/video codec/etc. blocks that don't even have reset drivers.

Thanks for the input! I'll just respin it by dropping mtk_v1 diff.

Nic

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  parent reply	other threads:[~2022-06-30 15:49 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-06-23 20:00 [PATCH v3 0/5] Simplify vfio_iommu_type1 attach/detach routine Nicolin Chen
2022-06-23 20:00 ` [PATCH v3 1/5] iommu: Return -EMEDIUMTYPE for incompatible domain and device/group Nicolin Chen
2022-06-24  1:35   ` Baolu Lu
2022-06-24  2:44     ` Nicolin Chen
2022-06-24  5:38       ` Yong Wu
2022-06-24  5:41         ` Nicolin Chen
2022-06-24  6:16         ` Tian, Kevin
2022-06-24 10:35           ` Yong Wu
2022-06-24 18:19             ` Jason Gunthorpe
2022-06-29 19:47               ` Nicolin Chen
2022-06-30  8:21                 ` Robin Murphy
2022-06-30  9:57                   ` Tian, Kevin
2022-06-30 15:47                   ` Nicolin Chen [this message]
2022-06-30  9:33                 ` Yong Wu
2022-06-30 15:45                   ` Nicolin Chen
2022-06-23 20:00 ` [PATCH v3 2/5] vfio/iommu_type1: Prefer to reuse domains vs match enforced cache coherency Nicolin Chen
2022-06-24  1:50   ` Baolu Lu
2022-06-23 20:00 ` [PATCH v3 3/5] vfio/iommu_type1: Remove the domain->ops comparison Nicolin Chen
2022-06-24 18:28   ` Jason Gunthorpe
2022-06-24 18:46     ` Jason Gunthorpe
2022-06-23 20:00 ` [PATCH v3 4/5] vfio/iommu_type1: Clean up update_dirty_scope in detach_group() Nicolin Chen
2022-06-23 20:00 ` [PATCH v3 5/5] vfio/iommu_type1: Simplify group attachment Nicolin Chen
2022-06-27  6:57   ` Tian, Kevin

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