[PATCH] fixes for the SLB shadow buffer

[Benjamin Herrenschmidt]

> The first block of code detects the need for a demotion and changes the
> global mmu_vmalloc_psize, along with changing the value on the local CPU
> (and flushing it's SLB). But other CPUs still have the old values.
> 
> The second block of code checks if the global value matches the per-CPU
> value and if not, proceeds to a local SLB flush. That's how the "other"
> CPUs get the new value.
> 
> If your shadow is per-CPU, it thus needs to be updated in both cases.

Hrm.. I must have been looking at older sources or lacked caffeine, we
indeed only do the paca update and the flush&rebolt once.

Ben.