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Date:	Fri, 24 Jan 2014 14:44:21 +0000
From:	David Vrabel <>
To:	Konrad Rzeszutek Wilk <>
CC:	Zoltan Kiss <>,
	Stefano Stabellini <>,
	<>, <>,
	<>, <>,
	<>, <>,
Subject: Re: [Xen-devel] [PATCH v5] xen/grant-table: Avoid m2p_override during

On 24/01/14 14:37, Konrad Rzeszutek Wilk wrote:
> On Thu, Jan 23, 2014 at 01:07:10PM +0000, Zoltan Kiss wrote:
>> The grant mapping API does m2p_override unnecessarily: only gntdev needs it,
>> for blkback and future netback patches it just cause a lock contention, as
>> those pages never go to userspace. Therefore this series does the following:
>> - the original functions were renamed to __gnttab_[un]map_refs, with a new
>>   parameter m2p_override
>> - based on m2p_override either they follow the original behaviour, or just set
>>   the private flag and call set_phys_to_machine
>> - gnttab_[un]map_refs are now a wrapper to call __gnttab_[un]map_refs with
>>   m2p_override false
>> - a new function gnttab_[un]map_refs_userspace provides the old behaviour
>> It also removes a stray space from page.h and change ret to 0 if
>> XENFEAT_auto_translated_physmap, as that is the only possible return value
>> there.
>> v2:
>> - move the storing of the old mfn in page->index to gnttab_map_refs
>> - move the function header update to a separate patch
>> v3:
>> - a new approach to retain old behaviour where it needed
>> - squash the patches into one
>> v4:
>> - move out the common bits from m2p* functions, and pass pfn/mfn as parameter
>> - clear page->private before doing anything with the page, so m2p_find_override
>>   won't race with this
>> v5:
>> - change return value handling in __gnttab_[un]map_refs
>> - remove a stray space in page.h
>> - add detail why ret = 0 now at some places
>> Signed-off-by: Zoltan Kiss <>
>> Suggested-by: David Vrabel <>
> It looks OK to me and while it is not a bug-fix I think it should
> go for v3.14 - as it _should_ improve the backends.
> David or Boris; Stefano, please Ack/Nack it.

Reviewed-by: David Vrabel <>

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