Re: [PATCH 11 of 11] x86: defer cr3 reload when doing pud_clear()

[H. Peter Anvin]

Jeremy Fitzhardinge wrote:
> PAE mode requires that we reload cr3 in order to guarantee that
> changes to the pgd will be noticed by the processor.  This means that
> in principle pud_clear needs to reload cr3 every time.  However,
> because reloading cr3 implies a tlb flush, we want to avoid it where
> possible.

It only matters (for a processor which supports PGE) if we actually use 
the namespace in between.

> In huge_pmd_unshare, it is followed by flush_tlb_range, which always
> results in a full cr3-reload tlb flush.

This one makes me nervous, as it feels like a side effect of 
implementation, and not a guarantee by design.

	-hpa
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