Re: [PATCH v9 07/18] x86/virt/tdx: Do TDX module per-cpu initialization

Dave Hansen
2023-02-13T22:28:53Z

On 2/13/23 13:13, Huang, Kai wrote:
> Perhaps I didn't explain clearly in the comment. Below is the updated one:
>
> /*
> * The previous call of __tdx_enable() may only have
> * initialized part of present cpus during module
> * initialization, and new cpus may have become online
> * since then w/o doing per-cpu initialization.
> *
> * For example, a new CPU can become online when KVM is
> * unloaded, in which case tdx_cpu_enable() is not called since
> * KVM's CPU online callback has been removed.
> *
> * To make sure all online cpus are TDX-runnable, always
> * do per-cpu initialization for all online cpus here
> * even the module has been initialized.
> */

This is voodoo.

I want a TDX-specific hotplug CPU handler. Period. Please make that
happen. Put that code in this patch. That handler should:

1. Run after the KVM handler (if present)
2. See if VMX is on
3. If VMX is on:
3a. Run smp_func_module_lp_init(), else
3b. Mark the CPU as needing smp_func_module_lp_init()

Then, in the 'case TDX_MODULE_INITIALIZED:', you call a function to
iterate over the cpumask that was generated in 3b.

That makes the handoff *EXPLICIT*. You know exactly which CPUs need
what done to them. A CPU hotplug either explicitly involves doing the
work to make TDX work on the CPU, or explicitly defers the work to a
specific later time in a specific later piece of code.