RE: [PATCH v10 33/38] x86/entry: Add fred_entry_from_kvm() for VMX to handle IRQ/NMI

[Li, Xin3]

> > +	/*
> > +	 * Don't check the FRED stack level, the call stack leading to this
> > +	 * helper is effectively constant and shallow (relatively speaking).
> 
> It's more that we don't need to protect from reentrancy.  The external
> interrupt uses stack level 0 so no adjustment would be needed anyway,
> and NMI does not use an IST even in the non-FRED case.

I will incorporate this comment.

I think a VMX NMI is kind of like a user level NMI, and we don't need
to worry about nested NMIs.

> 
> > +	 * Emulate the FRED-defined redzone and stack alignment.
> > +	 */
> > +	sub $(FRED_CONFIG_REDZONE_AMOUNT << 6), %rsp
> > +	and $FRED_STACK_FRAME_RSP_MASK, %rsp