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Message-ID: <20210611104524.GD15274@willie-the-truck>
Date: Fri, 11 Jun 2021 11:45:24 +0100
From: Will Deacon <will@...nel.org>
To: Ashish Mhetre <amhetre@...dia.com>
Cc: joro@...tes.org, robin.murphy@....com, vdumpa@...dia.com,
iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 1/2] iommu: Fix race condition during default domain
allocation
On Thu, Jun 10, 2021 at 09:46:53AM +0530, Ashish Mhetre wrote:
> Domain is getting created more than once during asynchronous multiple
> display heads(devices) probe. All the display heads share same SID and
> are expected to be in same domain. As iommu_alloc_default_domain() call
> is not protected, the group->default_domain and group->domain are ending
> up with different domains and leading to subsequent IOMMU faults.
> Fix this by protecting iommu_alloc_default_domain() call with group->mutex.
Can you provide some more information about exactly what the h/w
configuration is, and the callstack which exhibits the race, please?
> Signed-off-by: Ashish Mhetre <amhetre@...dia.com>
> ---
> drivers/iommu/iommu.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> index 808ab70..2700500 100644
> --- a/drivers/iommu/iommu.c
> +++ b/drivers/iommu/iommu.c
> @@ -273,7 +273,9 @@ int iommu_probe_device(struct device *dev)
> * support default domains, so the return value is not yet
> * checked.
> */
> + 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.
Will
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