Re: [Xen-devel] [PATCH 0 of 2] Add libxc API that sets mem_access type for an array of gfns

[Christian Limpach <christian.limpach@xxxxxxxxx>]

On Thu, Apr 26, 2012 at 11:33 AM, Aravindh Puthiyaparambil
<aravindh@xxxxxxxxxxxx> wrote:
> When the mem_access type needs to be changed for multiple discontiguous gfns, 
> calling xc_hvm_set_mem_access() multiple times does not perform very well. 
> The main pain points are the multiple libxc calls themselves plus the 
> multiple map_domain_page() / unmap_domain_page() and ept_sync_domain() calls 
> for each ept_set_entry(gfn). The following patches adds a new mem_access API 
> that sets the mem_access type for an array of guest physical addresses in one 
> libxc call with minimal map_domain_page() / unmap_domain_page() and 
> ept_sync_domain() calls.


Are you sure that your bulk code actually works?  It seems to me that
your __ept_set_entry function assumes that table still points to the
top of the p2m.  The "for ( i = ept_get_wl(d); i > target; i-- )" loop
will walk the table, and so in the subsequent calls from your bulk
loop, this won't work?

I think you need something like an iterator, the context of which can
be passed around...

Also, the call to ept_get_entry in your bulk loop will do a walk in
every iteration, it seems a bit arbitrary to only (try to) avoid one
and not the other.  But I guess the "win" is from reducing the number
of ept_sync_domain calls.

    christian

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