linux-kernel - Re: [PATCH 1/1] Revert "iommu/vt-d: Fix possible recursive locking in intel_iommu

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Date:   Tue, 20 Sep 2022 20:36:42 +0800
From:   Baolu Lu <baolu.lu@...ux.intel.com>
To:     Robin Murphy <robin.murphy@....com>,
        Thorsten Leemhuis <regressions@...mhuis.info>,
        iommu@...ts.linux.dev
Cc:     baolu.lu@...ux.intel.com, Joerg Roedel <joro@...tes.org>,
        Will Deacon <will@...nel.org>,
        Kevin Tian <kevin.tian@...el.com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        George Hilliard <thirtythreeforty@...il.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] Revert "iommu/vt-d: Fix possible recursive locking in
 intel_iommu_init()"

On 2022/9/20 20:16, Robin Murphy wrote:
> On 2022-09-20 12:58, Thorsten Leemhuis wrote:
>> On 20.09.22 10:17, Lu Baolu wrote:
>>> This reverts commit 9cd4f1434479f1ac25c440c421fbf52069079914.
>>
>> Thx for taking care of this.
>>
>>> Some issues were reported on the original commit. Some thunderbolt 
>>> devices
>>> don't work anymore due to the following DMA fault.
>>>
>>> DMAR: DRHD: handling fault status reg 2
>>> DMAR: [INTR-REMAP] Request device [09:00.0] fault index 0x8080
>>>        [fault reason 0x25]
>>>        Blocked a compatibility format interrupt request
>>>
>>> Bring it back for now to avoid functional regression.
>>>
>>> Fixes: 9cd4f1434479f ("iommu/vt-d: Fix possible recursive locking in 
>>> intel_iommu_init()")
>>> Link: 
>>> https://lore.kernel.org/linux-iommu/485A6EA5-6D58-42EA-B298-8571E97422DE@getmailspring.com/
>>> Link: https://bugzilla.kernel.org/show_bug.cgi?id=216497
>>
>> Both those reports were against 5.19.y, so this afaics should have a
>>
>> Cc: <stable@...r.kernel.org> # 5.19.x
>>
>> to ensure it's backported.
>>
>> Speaking of which: Joerg/Will/Robin, it seems quite a few people are
>> running into this, it hence would be great to get this quickly mainlined
>> (maybe by letting Linus pick it up straight from the list once ready?)
>> so stable can pick it up.
> 
> As a heads-up, a straight revert is likely to lead to people reporting 
> lockdep warnings against -next, for the patches queued there which 
> exposed this dodgy locking in the first place.

I plan to fix that lockdep warning with below patch:

https://github.com/LuBaolu/intel-iommu/commit/dff18af627a2a76651b74cd6531f3e9357a97072

It works on my test machines. I am about to test it with more hardware.

> 
> Does it work to just move the dmar_register_bus_notifier() call back to 
> where it was, without undoing the rest of the patch? That seems like the 
> change that's overwhelmingly likely to have broken IRQ remapping, and 
> TBH it wasn't clear to me why the original patch moved it to begin with.

The callbacks of dmar_register_bus_notifier() possibly races with
intel_iommu_init(). So the offending commit had to move it down until
the Intel IOMMU initialization is done.

Best regards,
baolu