RE: [PATCH v12 10/18] x86/fsgsbase/64: Enable FSGSBASE instructions in helper functions

[David Laight]

From: Thomas Gleixner
> Sent: 19 May 2020 15:48
> 
> David Laight <David.Laight@xxxxxxxxxx> writes:
> > From: Sasha Levin
> >> >> +		native_swapgs();
> >> >> +		gsbase = rdgsbase();
> >> >> +		native_swapgs();
> >
> > Does local_irq_save() even do anything useful here.
> > You need to actually execute CLI, not just set a
> > flag that indicates interrupts shouldn't happen.
> > (Which is what I think local_irq_save() might do.)
> 
>   local_irq_save()
>     raw_local_irq_save()
>       arch_local_irq_save()
>         arch_local_irq_disable()
>           native_irq_disable()
>             asm("CLI")

Ah, I was expecting software 'tricks' to avoid the expensive CLI.
But that call chain probably costs more - unless it is all inlined.

	David

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