[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] Xen-4.5 HVMOP ABI issues
At 14:28 +0000 on 04 Dec (1417699730), Andrew Cooper wrote: > On 04/12/14 13:49, Jan Beulich wrote: > >>>> On 28.11.14 at 16:46, <andrew.cooper3@xxxxxxxxxx> wrote: > >> On 28/11/14 15:18, Jan Beulich wrote: > >>>>>> On 28.11.14 at 14:55, <andrew.cooper3@xxxxxxxxxx> wrote: > >>>> The problem is with continuations which reuse the upper bits of the > >>>> input register, not with this HVMOP_op_mask specifically; the > >>>> HVMOP_op_mask simply adds to an existing problem. This is something > >>>> which needs considering urgently because, as you identify above, we have > >>>> already suffered an accidental ABI breakage with the mem-op widening. > >>> Since we can't retroactively fix the mem-op widening, I still don't see > >>> what's urgent here: As long as we don't change any of these masks, > >>> nothing bad is going to happen. Of course one thing to consider with > >>> this aspect in mind is whether to change the hvm-op or gnttab-op > >>> masks again _before_ 4.5 goes out, based on whether we feel they're > >>> wide enough for the (un)foreseeable future. > >> By urgent, I mean exactly this, while we have the ability to tweak the > >> masks. > > With no-one else voicing an opinion: > > > > For hvmop, the mask currently is 8 bits and we've got 22 ops defined. > > > > For gnttabop, the mask currently is 12 bits and we've got 12 ops defined. > > > > For the latter, we're fine even without further consideration. For the > > former, the two operations actively using the continuation encoding > > are tools-only ones. Since we're fine to alter the tools only interfaces, > > and since it was intended for the tools-only HVM-ops to be split off > > to a separate hypercall (e.g. hvmctl) anyway, the range restriction > > would then no longer be a problem. Plus, in the worst case we could > > always introduce yet another hypercall if we ran out of numbers. > > Are you suggesting that we make a new hvmctl now and remove the hvmop > mask before 4.5? If we ship 4.5 with the hvmop mask, we cannot > subsequently remove it even if all continuable hypercalls move to a > separate hypercall. I think we can if the only hypercalls that use continuations are tools-only (and so not liable to work across migration anyway). Tim. _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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