Re: [Xen-devel] [PATCHv1] xen/balloon: disable memory hotplug in PV guests

[David Vrabel <david.vrabel@xxxxxxxxxx>]

On 10/03/15 13:35, Boris Ostrovsky wrote:
> On 03/10/2015 07:40 AM, David Vrabel wrote:
>> On 09/03/15 14:10, David Vrabel wrote:
>>> Memory hotplug doesn't work with PV guests because:
>>>
>>>    a) The p2m cannot be expanded to cover the new sections.
>> Broken by 054954eb051f35e74b75a566a96fe756015352c8 (xen: switch to
>> linear virtual mapped sparse p2m list).
>>
>> This one would be non-trivial to fix.  We'd need a sparse set of
>> vm_area's for the p2m or similar.
>>
>>>    b) add_memory() builds page tables for the new sections which means
>>>       the new pages must have valid p2m entries (or a BUG occurs).
>> After some more testing this appears to be broken by:
>>
>> 25b884a83d487fd62c3de7ac1ab5549979188482 (x86/xen: set regions above the
>> end of RAM as 1:1) included 3.16.
>>
>> This one can be trivially fixed by setting the new sections in the p2m
>> to INVALID_P2M_ENTRY before calling add_memory().
> 
> Have you tried 3.17? As I said yesterday, it worked for me (with 4.4 Xen).

No.  But there are three bugs that prevent it from working in 3.16+ so
I'm really not sure how you had a working in a 3.17 PV guest.

Regardless, it definitely doesn't work now because of the linear p2m
change.  What do you want to do about this?

David

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