Re: [PATCH] x86/S3: Restore CR4 earlier during resume

[Jan Beulich <jbeulich@xxxxxxxx>]

On 02.10.2020 23:36, Andrew Cooper wrote:
> c/s 4304ff420e5 "x86/S3: Drop {save,restore}_rest_processor_state()
> completely" moved CR4 restoration up into C, to account for the fact that MCE
> was explicitly handled later.
> 
> However, time_resume() ends up making an EFI Runtime Service call, and EFI
> explodes without OSFXSR, presumably when trying to spill %xmm registers onto
> the stack.
> 
> Given this codepath, and the potential for other issues of a similar kind (TLB
> flushing vs INVPCID, HVM logic vs VMXE, etc), restore CR4 in asm before
> entering C.
> 
> Ignore the previous MCE special case, because its not actually necessary.  The
> handler is already suitably configured from before suspend.

Are you suggesting we could drop the call to mcheck_init() altogether?

> Fixes: 4304ff420e5 ("x86/S3: Drop {save,restore}_rest_processor_state() 
> completely")
> Reported-by: Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>

Jan