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

[Kuba Pawlak]

On 12.02.2025 03:37, 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 patch was originally targeting the Jammy linux-gcp kernel, but the
> same patch applies to the generic kernel. For this reason, a separate
> thread was made for each kernel such that linux-gcp can get the patch
> early and after the generic patch window has already closed, but the
> same patch can be reviewed and applied to generic at a later time and
> with more strict oversight.
>
> [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.
>
> This test was completed with the Jammy linux-gcp kernel because it
> includes drivers for the test configuration's network interface which
> generic does not have. There isn't a difference between the two kernels
> that I'm aware of that would indicate the test does not also apply to
> generic.
>
> [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: Kuba Pawlak <kuba.pawlak at canonical.com>
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