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From: Krishna Reddy <>
To: Will Deacon <>, Ashish Mhetre <>
Cc: "" <>,
	"" <>,
	"" <>,
Subject: RE: [PATCH 1/2] iommu: Fix race condition during default domain allocation
Date: Fri, 11 Jun 2021 18:30:25 +0000	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <20210611104524.GD15274@willie-the-truck>

> > +     mutex_lock(&group->mutex);
> >       iommu_alloc_default_domain(group, dev);
> > +     mutex_unlock(&group->mutex);
> It feels wrong to serialise this for everybody just to cater for systems with
> aliasing SIDs between devices.

Serialization is limited to devices in the same group. Unless devices share SID, they wouldn't be in same group.

> Can you provide some more information about exactly what the h/w
> configuration is, and the callstack which exhibits the race, please?

The failure is an after effect and is a page fault.  Don't have a failure call stack here. Ashish has traced it through print messages and he can provide them.

From the prints messages, The following was observed in page fault case:

Device1:  iommu_probe_device() --> iommu_alloc_default_domain() --> iommu_group_alloc_default_domain() --> __iommu_attach_device(group->default_domain)
Device2:  iommu_probe_device() --> iommu_alloc_default_domain() --> iommu_group_alloc_default_domain() --> __iommu_attach_device(group->default_domain)

Both devices(with same SID) are entering into iommu_group_alloc_default_domain() function and each one getting attached to a different group->default_domain 
as the second one overwrites  group->default_domain after the first one attaches to group->default_domain it has created.

SMMU would be setup to use first domain for the context page table. Whereas all the dma map/unamp requests from second device would
be performed on a domain that is not used by SMMU for context translations and IOVA (not mapped in first domain) accesses from second device lead to page faults. 


  parent reply	other threads:[~2021-06-11 18:30 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-10  4:16 [PATCH 0/2] iommu/arm-smmu: Fix races in iommu domain/group creation Ashish Mhetre
2021-06-10  4:16 ` [PATCH 1/2] iommu: Fix race condition during default domain allocation Ashish Mhetre
2021-06-11 10:45   ` Will Deacon
2021-06-11 12:49     ` Robin Murphy
2021-06-17  5:51       ` Ashish Mhetre
2021-06-17 17:49         ` Will Deacon
2021-06-11 18:30     ` Krishna Reddy [this message]
2021-06-10  4:16 ` [PATCH 2/2] iommu/arm-smmu: Fix race condition during iommu_group creation Ashish Mhetre

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