Re: [Xen-devel] [PATCH] xen/p2m: Remove np2m-specific filter from generic p2m_flush_table

[George Dunlap <george.dunlap@xxxxxxxxxx>]

On 08/02/17 10:02, Tim Deegan wrote:
> At 03:44 -0700 on 31 Jan (1485834259), Jan Beulich wrote:
>>>>> On 30.01.17 at 16:17, <george.dunlap@xxxxxxxxxx> wrote:
>>> Commit 71bb7304e7a7a35ea6df4b0cedebc35028e4c159 added flushing of
>>> nested p2m tables whenever the host p2m table changed.  Unfortunately
>>> in the process, it added a filter to the generic p2m_flush_table()
>>> function so that the p2m would only be flushed if it was being used as
>>> a nested p2m.  This meant that the p2m was not being flushed at all
>>> for altp2m callers.
>>>
>>> Instead do the nested p2m filtering in p2m_flush_nestedp2m().
> 
> I think it would be better to fix the test in p2m_flush_table() so it
> understands altp2m's use of tables.  That way we won't have to deal
> with filtering at other call sites, as Jan points out.  Also, this:
> 
>>>      for ( i = 0; i < MAX_NESTEDP2M; i++ )
>>> -        p2m_flush_table(d->arch.nested_p2m[i]);
>>> +    {
>>> +        struct p2m_domain *p2m = d->arch.nested_p2m[i];
>>> +        if ( p2m->np2m_base != P2M_BASE_EADDR )
>>> +            p2m_flush_table(p2m);
>>> +    }
> 
> moves the check of np2m_base outside the lock.  That might be OK but
> it's definitely a bit subtle.

Hrm, yes that's not so great.  v2 coming up.

 -George

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