ACK: [SRU][J:linux-gcp][PATCH v2 0/1] Fix bugs preventing boot on Intel TDX-enabled hosts

[Koichiro Den]

On Tue, Feb 11, 2025 at 06:37:27PM GMT, Ian Whitfield wrote:
> BugLink: https://bugs.launchpad.net/bugs/2097811
> 
> SRU Justification:
> 
> [Impact]
> 
> Google has requested an upstream fix to enable the boot of 5.15 kernel
> instances on their Intel TDX enabled infrastructure. The fix is
> described as preventing the recalculation of physical address width of
> the cpu during boot in a few select places, presumably using a more
> consistent and accurate value throughout the boot process.
> 
> [Fix]
> 
> There were a large number of unrelated conflicts resolved by adjusting
> the context around the changes in the patch. One conflict did have a
> direct impact on the patch, but it was resolved by tracing where a
> function call had been moved, and making the original changes there.
> 
> This thread applies to the Jammy linux-gcp kernel for the sake of
> getting the patch applied sooner to a smaller number of kernels where
> this issue is more critical. Another thread will be sent to include this
> fix in the generic Jammy kernel where the risk is higher. The patch is
> unchanged.
> 
> [Test Plan]
> 
> Google reported inability to boot Focal images (which use a backport of
> this kernel) on a specific configuration in a deployment zone where
> Intel TDX was enabled. This patchset was tested by booting a Jammy image
> on one such machine (which uses the 6.8 kernel), installing this patched
> kernel, and booting into it. Before this patch is applied, the installed
> kernel doesn't finish the boot process, and after the patch is applied,
> it boots as normal.
> 
> [Where problems could occur]
> 
> As these changes affect booting and the kernel's understanding of the
> cpu, an error in the backporting of this patch could cause the user
> to be unable to boot the kernel. The patch was primarily modified in
> the MTRR cleanup feature, which can be disabled with a kernel parameter.
> If the fixes don't work, we would see the kernel continue to not be
> bootable on TDX-enabled hosts.
> 
> v2: Removed additional cherry-picked commit that was not necessary and
> required more of a backport effort.
> 
> Juergen Gross (1):
>   x86/mtrr: Remove physical address size calculation
> 
>  arch/x86/kernel/cpu/mtrr/cleanup.c | 16 ++++----
>  arch/x86/kernel/cpu/mtrr/generic.c | 12 +++++-
>  arch/x86/kernel/cpu/mtrr/mtrr.c    | 61 ++++--------------------------
>  arch/x86/kernel/cpu/mtrr/mtrr.h    |  4 +-
>  4 files changed, 29 insertions(+), 64 deletions(-)
> 

Acked-by: Koichiro Den <koichiro.den at canonical.com>