Re: [PATCH V2 0/6] Enable SMM page level protection.

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

 What I found is that the BSP doesn't wait for the AP rendezvous before closing SMRAM.
[Jiewen] That is a good catch. Thanks to explain.
I believe that is more convincible than AP getting interrupt. :)

We have some places where BSP talking to AP in S3.

1)      CpuS3.c - EarlyInitializeCpu()

2)      CpuS3.c - SmmRelocateBases()

3)      CpuS3.c - InitializeCpu()

4)      S3Resume.c - SendSmiIpiAllExcludingSelf()

I believe we can guarantee 1/2/3 is good, because I found we check BSP check mNumberToFinish.
4 is a risk, because there is no AP finish check. If the AP is in below 1M with CR3 in SMRAM, it will be a trouble.

Once the AP executes RSM and return to non-SMM, the CR3 is no longer valid and AP must be crashed immediately. WoW!

The fix, I believe, is same.
We should make 1) AP is in above 1M reserved memory, and 2) AP is in protected mode with paging disabled.

Thank you
Yao Jiewen

From: Paolo Bonzini [mailto:paolo.bonzini@gmail.com] On Behalf Of Paolo Bonzini
Sent: Wednesday, November 9, 2016 7:30 PM
To: Yao, Jiewen <jiewen.yao@intel.com>; Laszlo Ersek <lersek@redhat.com>
Cc: Tian, Feng <feng.tian@intel.com>; edk2-devel@ml01.01.org; Kinney, Michael D <michael.d.kinney@intel.com>; Fan, Jeff <jeff.fan@intel.com>; Zeng, Star <star.zeng@intel.com>
Subject: Re: [edk2] [PATCH V2 0/6] Enable SMM page level protection.



On 09/11/2016 07:25, Yao, Jiewen wrote:
> Current BSP just uses its own context to initialize AP. So that AP
> takes BSP CR3, which is SMM CR3, unfortunately. After BSP initialized
> APs, the AP is put to HALT-LOOP in X64 mode. It is the last straw,
> because X64 mode halt still need paging.
>
> 3)      The error happen, once the AP receives an interrupt (for
> whatever reason), AP starts executing code. However, that that time
> the AP might not be in SMM mode. It means SMM CR3 is not available.
> And then we see this.
>
> 4)      I guess we did not see the error, or this is RANDOM issue,
> because it depends on if AP receives an interrupt before BSP send
> INIT-SIPI-SIPI.
>
> 5)      The fix, I think, should be below: We should always put AP to
> protected mode, so that no paging is needed. We should put AP in
> above 1M reserved memory, instead of <1M memory, because <1M memory
> is restored.

For what it's worth, this is not what I observed.  What I found is that
the BSP doesn't wait for the AP rendezvous before closing SMRAM.

I'm not sure if the two things are related, but (3) would be a much
worse bug.  APs should not be receiving an interrupt.  Perhaps an NMI if
API is sitting in a CLI;HLT loop, but this is not what is happening.

Paolo