Re: Yet another S3 issue in Xen 4.14

[Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>]

On Thu, Oct 01, 2020 at 01:59:32PM +0200, Jan Beulich wrote:
> On 01.10.2020 03:12, Marek Marczykowski-Górecki wrote:
> > 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.
> 
> Since bisection may also point you at some intermediate breakage, which
> these last results of yours seem to support, could you check whether
> 55f8c389d434 put immediately on top of the above commit makes a difference,
> and if so resume bisecting from there?

Nope, 4304ff420e51b973ec9eb9dafd64a917dd9c0fb1 with 55f8c389d434 on top
it still hangs on resume.

-- 
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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