Re: [PATCH v4 24/24] [NOT-FOR-REVIEW] x86/virt/seamldr: Save and restore current VMCS

[Chao Gao]

On Thu, Feb 12, 2026 at 06:35:27AM -0800, Chao Gao wrote:
>P-SEAMLDR calls clobber the current VMCS as documented in Intel® Trust
>Domain CPU Architectural Extensions (May 2021 edition) Chapter 2.3 [1]:
>
>  SEAMRET from the P-SEAMLDR clears the current VMCS structure pointed
>  to by the current-VMCS pointer. A VMM that invokes the P-SEAMLDR using
>  SEAMCALL must reload the current-VMCS, if required, using the VMPTRLD
>  instruction.
>
>Save and restore the current VMCS using VMPTRST and VMPTRLD instructions
>to avoid breaking KVM.
>
>Signed-off-by: Chao Gao <chao.gao@xxxxxxxxx>
>---
>This patch is needed for testing until microcode is updated to preserve
>the current VMCS across P-SEAMLDR calls. Otherwise, if some normal VMs
>are running before TDX Module updates, vmread/vmwrite errors may occur
>immediately after updates.

The agreed approach is to fix the CPU behavior rather than work around the
issue in the kernel. So, I'll include the following patch to handle this
erratum. Please let me know if you have any concerns.