ACK: [SRU][I][PATCH 0/1] PCI: vmd: Do not disable MSI-X remapping if interrupt remapping is enabled by IOMMU

[Tim Gardner]

Acked-by: Tim Gardner <tim.gardner at canonical.com>

Seems like I just saw this patch.

On 2/16/22 8:29 AM, Jeff Lane wrote:
> BugLink: https://bugs.launchpad.net/bugs/1937295
> 
> [Impact]
> 
> A hardware partner discovered they were unable to install Ubuntu on some
> servers using VROC setups. They point to this issue involving DMAR that is
> blocking discovery of the VROC RAID devices:
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=2565e5b69c44b4e42469afea3cc5a97e74d1ed45
> 
> `git bisect` points to this offending commit ee81ee84f873 ("PCI:
> vmd: Disable MSI-X remapping when possible"), which disables VMD MSI
> remapping. The IOMMU hardware blocks the compatibility format
> interrupt request because Interrupt Remapping Enable Status (IRES) and
> Extended Interrupt Mode Enable (EIME) are enabled. Please refer to
> section "5.1.4 Interrupt-Remapping Hardware Operation" in Intel VT-d
> spec.
> 
> To fix the issue, VMD driver still enables the interrupt remapping
> irrespective of VMD_FEAT_CAN_BYPASS_MSI_REMAP if the IOMMU subsystem
> enables the interrupt remapping.
> 
> [Fix]
> 
> 2565e5b69c44 PCI: vmd: Do not disable MSI-X remapping if interrupt remapping is
> enabled by IOMMU
> 
> This is a simple patch that picks cleanly from 5.16
> 
> [Test Plan]
> 
>    1. Boot into VRoC controller in uEFI Setup and create a raid10 disk.
>    2. Install affected Ubuntu release on the RAID10.
>    3. The system hangs at "Partitions formatting 33%".
> 
> [Where problems could occur]
> 
> The fix itself is a very small change to drivers/pci/controller/vmd.c and
> problems should not occur. The root cause was discovered by the hardware
> partner's engineers, who tested and submitted it upstream where it was
> accepted and landed in 5.16.
> 
> That said, I doubt this will fix 18.04.6 as it would require a respin to get
> the patched kernel onto the ISO. 20.04 should pick it up in ISO in 20.04.5,
> so there could still be the initial issue since those ISOs would be lacking
> the patched kernel.
> 
> [Other Info]
> 
> As noted, this would need to not only land in the kernel but land in the kernel
> in the ISO to resolve the issue in the installation process. I'll bring this
> back as far as Focal with the expectation that while 20.04.4 is too late, it
> will be present using the GA kernel in 20.04.5 later on.
> 
> Adrian Huang (1):
>    PCI: vmd: Do not disable MSI-X remapping if interrupt remapping is
>      enabled by IOMMU
> 
>   drivers/pci/controller/vmd.c | 4 +++-
>   1 file changed, 3 insertions(+), 1 deletion(-)
> 

-- 
-----------
Tim Gardner
Canonical, Inc