Re: [Xen-devel] [PATCH] NPT: temporarily retain page table mapping in do_recalc()

[Tim Deegan <tim@xxxxxxx>]

At 11:31 +0100 on 05 May (1399285915), Jan Beulich wrote:
> Commit b3e024f3 ("x86/NPT: don't walk page tables when changing types
> on a range") neglected the fact that p2m_next_level() replaces the
> previous level's mapping with the new level's one, hence dereferencing
> a stale pointer the translation for which may no longer be available
> (timing dependent). Add a parameter to that function allowing the
> caller to request that the mapping be retained (the unmapping will be
> taken care of by the caller then).
> 
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

That's not a very nice interface, but I can't see a way around it,
since do_recalc() needs to have the lower-level mapping available before
it writes the upper-level entry, and having all callers of
p2m_next_level() do their own unmap would be awful too.

Reviewed-by: Tim Deegan <tim@xxxxxxx>

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