NACK: [SRU][J:linux-gcp][PATCH 0/2] Fix bugs preventing boot on Intel TDX-enabled hosts

[Ian Whitfield]

On Mon, Feb 10, 2025 at 07:13:38PM -0800, Ian Whitfield wrote:
> BugLink: https://bugs.launchpad.net/bugs/2097811
> 
> SRU Justification:
> 
> [Impact]
> 
> Google has requested these upstream commits be applied in order to fix
> bugs preventing the boot of 5.15 kernel instances on their Intel TDX
> enabled infrastructure.
> 
> These patches aim to resolve problems with incorrect assessment of the
> CPU's address width in bits on x86, mostly during boot.
> 
> [Fix]
> 
> The first patch applied cleanly. The second patch had 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 patches applied sooner to a smaller number of kernels where
> this issue is more critical. Another thread will be sent to include
> these fixes in the generic Jammy kernel where the risk is higher. The
> patches are 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 these patches could cause the user
> to be unable to boot the kernel. Risk of an error is relatively low due
> to the first patch applying cleanly and the second patch only needing
> modification in the MTRR cleanup feature, which could be disabled with
> a kernel command line parameter. If the fixes don't work, we would see
> the kernel continue to not be bootable on TDX-enabled hosts.
> 
> Juergen Gross (1):
>   x86/mtrr: Remove physical address size calculation
> 
> Paolo Bonzini (1):
>   x86/cpu: Allow reducing x86_phys_bits during early_identify_cpu()
> 
>  arch/x86/kernel/cpu/common.c       |  2 +
>  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 +-
>  5 files changed, 31 insertions(+), 64 deletions(-)
> 
> -- 
> 2.43.0
> 

Submitting a v2 without the first patch in this series, it's not necessary
and requires more careful backport work.