Re: [Xen-devel] [PATCH 5 of 9] x86/mm: Add per-page locking for memory sharing, when audits are disabled

["Jan Beulich" <JBeulich@xxxxxxxx>]

 >>> On 09.12.11 at 21:22, Andres Lagar-Cavilla <andres@xxxxxxxxxxxxxxxx> wrote:
> With the removal of the hash table, all that is needed now is locking
> of individual shared pages, as new (gfn,domain) pairs are removed or
> added from the list of mappings.
> 
> We recycle PGT_locked and use it to lock individual pages. We ensure 
> deadlock
> is averted by locking pages in increasing order. We leverage an "external"
> order enforcing construct from mm-locks.h to ensure the p2m_lock (needed to
> modify gfn entries during sharing) is always taken after page_locks.

As said before, I view taking a coarse lock inside a fine grained one as
inappropriate, and hence recommend to not apply this patch without
knowing if/when the promised follow-up patch will make it in.

Jan

> The global lock remains for the benefit of the auditing code, and is
> thus enabled only as a compile-time option.
> 
> Signed-off-by: Andres Lagar-Cavilla <andres@xxxxxxxxxxxxxxxx>



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