On 19.06.2020 13:36, Michał Leszczyński wrote: > ----- 19 cze 2020 o 13:34, Roger Pau Monné roger....@citrix.com 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.
I did suggest the limit can be lifted, but not by processing all pieces in one go. Whether batches of 32 or 64 or 128 are chosen is a different thing, but you can't do arbitrary amounts without any preemption checks. Jan
