Re: [PATCH v2 1/7] xen/mm: lift 32 item limit from mfn/gfn arrays

[Michał Leszczyński <michal.leszczynski@xxxxxxx>]

----- 19 cze 2020 o 13:34, Roger Pau Monné roger.pau@xxxxxxxxxx napisał(a):

> On Fri, Jun 19, 2020 at 01:38:00AM +0200, Michał Leszczyński wrote:
>> Replace on-stack array allocation with heap allocation
>> in order to lift the limit of 32 items in mfn/gfn arrays
>> when calling acquire_resource.
> 
> I'm afraid this is not correct, you cannot allow unbounded amounts of
> items to be processed like this, it's likely that you manage to
> trigger the watchdog if the list is long enough, specially when doing
> set_foreign_p2m_entry.
> 
> You need to process the items in batches (32 was IMO a good start), and
> then add support for hypercall continuations. Take a look at how
> XENMEM_populate_physmap just a couple of lines below makes use of
> hypercall_create_continuation.
> 
> After processing every batch you need to check if
> hypercall_preempt_check returns true and if so use
> hypercall_create_continuation in order to encode a continuation.
> 
> Thanks, Roger.


Somebody previously suggested that this limit could be lifted this way,
so I would like to hear some more opinions on that.


Best regards,
Michał Leszczyński
CERT Polska