linux-2.2.13pre15 stability w/ head.S patch

[Gabriel Paubert]

On Thu, 28 Oct 1999, David Edelsohn wrote:

> 
> 	The general, conservative procedure that should be followed for
> any BAT change is:
> 
> 	li	rX, 0
> 	mtdbatu N, rX
> 	isync
> 	mtdbatl N, rL
> 	mtdbatu N, rU
> 	isync
> 
> I do not see the posted assembly code performing any isync's to prevent
> speculation.  mtspr does not produce complete serialization in the
> pipeline, and the serialization is implementation-dependent.

Is it true even if you know that you have address translation turned off ?  
I thought that mtspr (to privileged registers, not ctr/lr) are executed
strictly in the order they appear, so that no intermediate incoherent
state could appear.

OTOH when address translation is turned on (or when the its state is
unknown) I would have put an isync _before_ the first mtdbatu to make
sure that it does not interfere with previous instructions (this is
required from the manuals AFAICT).

	Gabriel.


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