linux-kernel - Re: [PATCH v7 1/5] iommu: Lock group->mutex in iommu_deferred

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Message-ID: <451ce2f9-732a-4424-bd45-d20a4d819d46@amd.com>
Date: Wed, 26 Nov 2025 21:49:04 +0530
From: Dheeraj Kumar Srivastava <dheerajkumar.srivastava@....com>
To: Nicolin Chen <nicolinc@...dia.com>, "Srivastava, Dheeraj Kumar"
	<dhsrivas@....com>
CC: <joro@...tes.org>, <afael@...nel.org>, <bhelgaas@...gle.com>,
	<alex@...zbot.org>, <jgg@...dia.com>, <will@...nel.org>,
	<robin.murphy@....com>, <lenb@...nel.org>, <kevin.tian@...el.com>,
	<baolu.lu@...ux.intel.com>, <linux-arm-kernel@...ts.infradead.org>,
	<iommu@...ts.linux.dev>, <linux-kernel@...r.kernel.org>,
	<linux-acpi@...r.kernel.org>, <linux-pci@...r.kernel.org>,
	<kvm@...r.kernel.org>, <patches@...ts.linux.dev>, <pjaroszynski@...dia.com>,
	<vsethi@...dia.com>, <helgaas@...nel.org>, <etzhao1900@...il.com>
Subject: Re: [PATCH v7 1/5] iommu: Lock group->mutex in
 iommu_deferred_attach()

Hi

On 11/26/2025 9:46 PM, Nicolin Chen wrote:
> On Wed, Nov 26, 2025 at 06:25:34PM +0530, Srivastava, Dheeraj Kumar wrote:
>> On 11/22/2025 7:27 AM, Nicolin Chen wrote:
>>> The iommu_deferred_attach() function invokes __iommu_attach_device(), but
>>> doesn't hold the group->mutex like other __iommu_attach_device() callers.
>>>
>>> Though there is no pratical bug being triggered so far, it would be better
>>> to apply the same locking to this __iommu_attach_device(), since the IOMMU
>>> drivers nowaday are more aware of the group->mutex -- some of them use the
>>> iommu_group_mutex_assert() function that could be potentially in the path
>>> of an attach_dev callback function invoked by the __iommu_attach_device().
>>>
>>> Worth mentioning that the iommu_deferred_attach() will soon need to check
>>> group->resetting_domain that must be locked also.
>>>
>>> Thus, grab the mutex to guard __iommu_attach_device() like other callers.
>>>
>>
>> Tested the series with PCI reset on PFs and VFs, including device
>> pass-through to a Linux guest. All scenarios worked as expected.
>>
>> Tested-by: Dheeraj Kumar Srivastava <dheerajkumar.srivastava@....com>
> 
> Thanks for testing!
> 
> Yet, this is replying to PATCH-1. So, you might want to reply with
> your "Tested-by" tag to PATCH-0 :)
> 

Sure.

Thanks
Dheeraj

> Otherwise, default B4 command might miss your tag in other patches:
> 
>    ✗ [PATCH v7 1/5] iommu: Lock group->mutex in iommu_deferred_attach()
>      + Tested-by: Dheeraj Kumar Srivastava <dheerajkumar.srivastava@....com> (✓ DKIM/amd.com)
>    ✗ [PATCH v7 2/5] iommu: Tidy domain for iommu_setup_dma_ops()
>      + Reviewed-by: Jason Gunthorpe <jgg@...dia.com> (✗ DKIM/Nvidia.com)
>    ✗ [PATCH v7 3/5] iommu: Add iommu_driver_get_domain_for_dev() helper
>      + Reviewed-by: Jason Gunthorpe <jgg@...dia.com> (✗ DKIM/Nvidia.com)
>    ✗ [PATCH v7 4/5] iommu: Introduce pci_dev_reset_iommu_prepare/done()
>      + Reviewed-by: Jason Gunthorpe <jgg@...dia.com> (✗ DKIM/Nvidia.com)
>    ✗ [PATCH v7 5/5] PCI: Suspend iommu function prior to resetting a device
>      + Reviewed-by: Jason Gunthorpe <jgg@...dia.com> (✗ DKIM/Nvidia.com)
> 
> Thank you
> Nicolin