Re: [edk2-devel] [Patch 0/2] UefiCpuPkg: Default avoid print.

["Laszlo Ersek" <lersek@redhat.com>]

On 08/01/19 23:14, Andrew Fish wrote:

> The MpServices API and even the BSP don't apply at runtime, but then
> again you can't run code on the APs at runtime.

My understanding is that the OS can invoke a runtime service on any
processor. Plus, the UEFI spec classifies runtime services into groups,
and while in any given group at most one runtime service may be executed
at a time, a runtime service from another group can be invoked by the OS
on another processor.

See "Table 35. Rules for Reentry Into Runtime Services" (and the
containing section "8.1 Runtime Services Rules and Restrictions") in
UEFI-2.8.

As an example, one CPU could activate GetVariable() while another CPU
could activate GetTime(). If both services produce debug output (most
likely on a device that is excluded from OS control), some coordination
could be necessary.

That said, a conservative OS would likely avoid calling any runtime
service while another was busy (on any processor) :)

Thanks
Laszlo