Revisiting FPU context resume on i386

[Konstantin Belousov]

On Tue, Jul 16, 2013 at 06:54:57PM +1000, Bruce Evans wrote:
> ISTR disagreeing with jkim on using a special save area.
I believe the normal save area cannot be used there at all, since
the suspension is async and fpu.c could perform some operation on
the PCB-pointed save area while suspend IPI is received.


> % 	/* Restore CR2, CR4, CR3 and CR0 */
> % ...
> % 	movl	PCB_CR0(%ecx),%eax
> % 	movl	%eax,%cr0
> % 	jmp	1f
> % 1:
> 
> What's this magic null jump?

I think this is not needed.  It seems to be an attempt to follow
Intel spec, which requires to perform the long jump after enabling
the paging, probably code got copied somehow from locore.  The
jmp is needed in i386/acpica/acpu_wakecode.S, but it is wrong there
as well, since it should be a long jump.

Also, the comment before the %cr0 manipulations to set CR0_PG was
copied from amd64 version and is irrelevant there.
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