ACK/Cmnt: [PATCH 0/1 V2][SRU][J/OEM-5.17/OEM-5.14] intel_iommu: Enable intel_iommu, Ubuntu 22.04 installation crashes

[Tim Gardner]

On 7/20/22 07:10, Tim Gardner wrote:
> On 7/19/22 04:41, Koba Ko wrote:
>> BugLink: https://bugs.launchpad.net/bugs/1982104
>>
>> [Impact]
>> Ubuntu 22.04 installation crashes on our Intel Sapphire Rapids proto 
>> server which is targeting Telco workloads.
>> Attaching the console logs.
>>
>> Currently, it looks like disabling VT-D option in BIOS settings helps 
>> mitigate the issue.
>> Console logs indicate something is wrong in iommu/dmar subsystem.
>>
>> [Fix]
>> The IOMMU driver shares the pasid table for PCI alias devices. When the
>> RID2PASID entry of the shared pasid table has been filled by the first
>> device, the subsequent device will encounter the "DMAR: Setup RID2PASID
>> failed" failure as the pasid entry has already been marked as present.
>> As the result, the IOMMU probing process will be aborted.
>>
>> On the contrary, when any alias device is hot-removed from the system,
>> for example, by writing to /sys/bus/pci/devices/.../remove, the shared
>> RID2PASID will be cleared without any notifications to other devices.
>> As the result, any DMAs from those rest devices are blocked.
>>
>> Sharing pasid table among PCI alias devices could save two memory pages
>> for devices underneath the PCIe-to-PCI bridges. Anyway, considering that
>> those devices are rare on modern platforms that support VT-d in scalable
>> mode and the saved memory is negligible, it's reasonable to remove this
>> part of immature code to make the driver feasible and stable.
>>
>> [Test Case]
>> 1. use the target machine(Intel Sapphire Rapids) and install the 
>> kernel with the fix.
>> 2. boot the target machine
>> 3. check dmesg if the error message exists
>> [ 8.120527] pci 0000:03:01.0: DMAR: Setup RID2PASID failed
>>
>> [Where problems could occur]
>> After enable intel_iommu, the errors may be occurred.
>> We need to figure out one by one once the related errors are triggered 
>> in the future.
>>
>> V2:
>> 1. re-link with a public bug
>> 2. As per V1 comment, this patch has applied on unstable so drop [U] on
>> v2.
>>
>> Lu Baolu (1):
>>    [SRU][J/OEM-5.17/OEM-5.14] iommu/vt-d: Fix RID2PASID setup/teardown
>>      failure
>>
>>   drivers/iommu/intel/iommu.c | 24 -------------
>>   drivers/iommu/intel/pasid.c | 69 ++-----------------------------------
>>   drivers/iommu/intel/pasid.h |  1 -
>>   include/linux/intel-iommu.h |  3 --
>>   4 files changed, 3 insertions(+), 94 deletions(-)
>>
> Acked-by: Tim Gardner <tim.gardner at canonical.com>
> 
> The correct form for a Launchpad URL is 'note<LP: #1953613>'
> 
> 

Ooops, wrong thread.

-- 
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Tim Gardner
Canonical, Inc