Kernel fails to enable XSAVE when running in a “v5” AMD SEV-SNP VM

[John Cabaj]

SRU Justification

[Impact]

* Request from MSFT to include patch to disable CET Shadow Stack on SEV-SNP. Due to CPUID emulation bug not being fixed in VMs until October 2024, this feature is being disabled in the interim.

[Fix]

* Clean cherry-pick SAUCE patch from MSFT tree, https://github.com/dcui/linux
* cdf5cdd: "x86/hyperv: temporarily disable CET SS on SEV-SNP due to a paravisor bug"

[Test Plan]

* Compile tested
* Boot tested
* Microsoft tested

[Regression potential]

* Changes isolated, minimal regression risk

[Other info]

* SF #00387447

[Ubuntu Kernel Bot (ubuntu-kernel-bot)]

This bug is awaiting verification that the linux-azure/6.8.0-1010.10 kernel in -proposed solves the problem. Please test the kernel and update this bug with the results. If the problem is solved, change the tag 'verification-needed-noble-linux-azure' to 'verification-done-noble-linux-azure'. If the problem still exists, change the tag 'verification-needed-noble-linux-azure' to 'verification-failed-noble-linux-azure'.

If verification is not done by 5 working days from today, this fix will be dropped from the source code, and this bug will be closed.

See https://wiki.ubuntu.com/Testing/EnableProposed for documentation how to enable and use -proposed. Thank you!