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

["Yao, Jiewen" <jiewen.yao@intel.com>]

Yeah, there is some good resource on the web.

ACPI spec defined APEI for error handling.
https://www.uefi.org/sites/default/files/resources/ACPI_6_2.pdf

Below ppt introduced basic info on memory technology such as spare or mirror.
ftp://ftp.hp.com/pub/c-products/servers/options/c00256943.pdf

Below ppt introduced basic info on RAS/HotPlug in Linux.
https://events.static.linuxfound.org/sites/events/files/lcjp13_chen.pdf
https://events.static.linuxfound.org/sites/events/files/lcjp13_ishimatsu.pdf

Put all things together: when memory error happens, a platform may generate SMI or SCI redirect to SMI.
Then SMI code may choose to analyze, recovery, or backup DIMM for OS memory. As such, RAS SMI handler may need access OS memory, and/or interactive with OS handler via ASL code.

Thank you
Yao Jiewen

> -----Original Message-----
> From: Laszlo Ersek [mailto:lersek@redhat.com]
> Sent: Wednesday, November 7, 2018 9:37 PM
> To: Yao, Jiewen <jiewen.yao@intel.com>
> Cc: Ni, Ruiyu <ruiyu.ni@intel.com>; edk2-devel@lists.01.org; Dong, Eric
> <eric.dong@intel.com>
> Subject: Re: [PATCH] UefiCpuPkg/SmmCpu: Block SMM read-out only when
> static paging is used
> 
> 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