SEV-SNP instances on AWS fail to boot

[Magali Lemes do Sacramento]

[Impact]
AWS instances with SEV-SNP enabled running the 6.17 kernel fail to boot
following upstream commit 81256a50aa0f ("x86/mm: Make memremap(MEMREMAP_WB) map
memory as encrypted by default"). The failure occurs because the vmgenid
driver relies on memory that must be shared, but is now mapped as encrypted by
default.

[Fix]
Clean cherry-pick of bb9ff576fdff ("virt: vmgenid: remap memory as
decrypted") from linux-next.

[Test Plan]
Compile the kernel with this patch applied and boot test on AWS c7a.8xlarge
instances with SEV-SNP enabled and disabled, verifying that the system boots
successfully in both configurations.

[Where problems could occur]
This patch only touches the vmgenid driver, and only affects the memory
attributes of the vmgenid mapping. However, incorrect assumptions about the
sharing requirements of the vmgenid memory region could potentially lead to
loss of vmgenid functionality or boot failures.

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

This bug is awaiting verification that the linux-aws/6.17.0-1007.7 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-questing-linux-aws' to 'verification-done-questing-linux-aws'. If the problem still exists, change the tag 'verification-needed-questing-linux-aws' to 'verification-failed-questing-linux-aws'.

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!