Yet another S3 issue in Xen 4.14

[Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>]

Hi,

After patching the previous issue ("x86/S3: Fix Shadow Stack resume
path") I still encounter issues resume from S3.
Since I had it working on Xen 4.13 on this particular hardware (Thinkpad
P52), I bisected it and got this:

commit 4304ff420e51b973ec9eb9dafd64a917dd9c0fb1
Author: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Date:   Wed Dec 11 20:59:19 2019 +0000

    x86/S3: Drop {save,restore}_rest_processor_state() completely
    
    There is no need to save/restore FS/GS/XCR0 state.  It will be handled
    suitably on the context switch away from the idle.
    
    The CR4 restoration in restore_rest_processor_state() was actually fighting
    later code in enter_state() which tried to keep CR4.MCE clear until 
everything
    was set up.  Delete the intermediate restoration, and defer final 
restoration
    until after MCE is reconfigured.
    
    Restoring PAT can be done earlier, and ideally before paging is enabled.  By
    moving it into the trampoline during the setup for 64bit, the call can be
    dropped from cpu_init().  The EFI path boot path doesn't disable paging, so
    make the adjustment when switching onto Xen's pagetables.
    
    The only remaing piece of restoration is load_system_tables(), so suspend.c
    can be deleted in its entirety.
    
    Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>

Parent of this commit suspends and resumes just fine. With this commit
applied, it (I think) it panics, at least I get reboot after 5s. Sadly, I
don't have serial console there.

I tried also master and stable-4.14 with this commit reverted (and also
the other fix applied), but it doesn't work. In this case I get a hang on
resume (power led still flashing, but fan woke up). There are probably
some other dependencies.

Any idea?

PS This is different than "Xen crash after S3 suspend - Xen 4.13"
thread, as this one broke with 4.13 -> 4.14 update.

-- 
Best Regards,
Marek Marczykowski-Górecki
Invisible Things Lab
A: Because it messes up the order in which people normally read text.
Q: Why is top-posting such a bad thing?

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