Re: [PATCH v2 3/5] x86/virt/tdx: Add SEAMCALL wrapper for TDH.SYS.DISABLE

[Huang, Kai]

On Mon, 2026-03-23 at 14:59 -0600, Vishal Verma wrote:
> Some early TDX-capable platforms have an erratum where a partial write
> to TDX private memory can cause a machine check on a subsequent read.
> On these platforms, kexec and kdump have been disabled in these cases,
> because the old kernel cannot safely hand off TDX state to the new
> kernel. Later TDX modules support the TDH.SYS.DISABLE SEAMCALL, which
> provides a way to cleanly disable TDX and allow kexec to proceed.
> 
> The new SEAMCALL has an enumeration bit, but that is ignored. It is
> expected that users will be using the latest TDX module, and the failure
> mode for running the missing SEAMCALL on an older module is not fatal.
> 
> This can be a long running operation, and the time needed largely
> depends on the amount of memory that has been allocated to TDs. If all
> TDs have been destroyed prior to the sys_disable call, then it is fast,
> with only needing to override the TDX module memory.
> 
> After the SEAMCALL completes, the TDX module is disabled and all memory
> resources allocated to TDX are freed and reset. The next kernel can then
> re-initialize the TDX module from scratch via the normal TDX bring-up
> sequence.
> 
> The SEAMCALL can return two different error codes that expect a retry.
>  - TDX_INTERRUPTED_RESUMABLE can be returned in the case of a host
>    interrupt. However, it will not return until it makes some forward
>    progress, so we can expect to complete even in the case of interrupt
>    storms.
>  - TDX_SYS_BUSY will be returned on contention with other TDH.SYS.*
>    SEAMCALLs, however a side effect of TDH.SYS.DISABLE is that it will
>    block other SEAMCALLs once it gets going. So this contention will be
>    short lived.
> 
> So loop infinitely on either of these error codes, until success or other
> error.
> 
> Co-developed-by: Rick Edgecombe <rick.p.edgecombe@xxxxxxxxx>
> Signed-off-by: Rick Edgecombe <rick.p.edgecombe@xxxxxxxxx>
> Signed-off-by: Vishal Verma <vishal.l.verma@xxxxxxxxx>
> 

Acked-by: Kai Huang <kai.huang@xxxxxxxxx>