Re: [PATCH] UefiCpuPkg/SmmCpu: Block SMM read-out only when static paging is used

[Laszlo Ersek <lersek@redhat.com>]

On 11/07/18 09:27, Yao, Jiewen wrote:
> If Static paging is not used, then the SMM uses dynamic paging.
> 
> Here dynamic paging means the page fault request on-demand.
> 
> 2 special examples here:
> 1) above 4G MMIO. By default, SMM only setup paging table for 4G memory. If MMIO above 4G, then SMM need use #PF handler to grant MMIO access.
> 2) server RAS. By default, SMM only setup paging table for SMM communication buffer. For server RAS, memory hotplug may request direct OS memory access. If so, we also rely on #PF handler to grant OS access.
> 
> This patch fixed the second issue in the second case.

This is very interesting -- if you have a bit of time, can you please
describe in more detail what "For server RAS, memory hotplug may request
direct OS memory access" means? What agents take what steps?

(I don't mean to hold this patch -- I've given my A-b, so this is for my
own education only. Although, adding this very useful info to the commit
message, or at least to the associated BZ, would be extremely useful.)

Thanks!
Laszlo