Re: [Qemu-devel] [PATCH v9 05/11] numa: Extend CLI to provide initiator information for numa nodes

[Dan Williams]

On Wed, Aug 14, 2019 at 6:57 PM Tao Xu <address@hidden> wrote:
>
> On 8/15/2019 5:29 AM, Dan Williams wrote:
> > On Tue, Aug 13, 2019 at 10:14 PM Tao Xu <address@hidden> wrote:
> >>
> >> On 8/14/2019 10:39 AM, Dan Williams wrote:
> >>> On Tue, Aug 13, 2019 at 8:00 AM Igor Mammedov <address@hidden> wrote:
> >>>>
> >>>> On Fri,  9 Aug 2019 14:57:25 +0800
> >>>> Tao <address@hidden> wrote:
> >>>>
> >>>>> From: Tao Xu <address@hidden>
> >>>>>
> [...]
> >>>>> +    for (i = 0; i < machine->numa_state->num_nodes; i++) {
> >>>>> +        if (numa_info[i].initiator_valid &&
> >>>>> +            !numa_info[numa_info[i].initiator].has_cpu) {
> >>>>                             ^^^^^^^^^^^^^^^^^^^^^^ possible out of 
> >>>> bounds read, see bellow
> >>>>
> >>>>> +            error_report("The initiator-id %"PRIu16 " of NUMA node %d"
> >>>>> +                         " does not exist.", numa_info[i].initiator, 
> >>>>> i);
> >>>>> +            error_printf("\n");
> >>>>> +
> >>>>> +            exit(1);
> >>>>> +        }
> >>>> it takes care only about nodes that have cpus or memory-only ones that 
> >>>> have
> >>>> initiator explicitly provided on CLI. And leaves possibility to have
> >>>> memory-only nodes without initiator mixed with nodes that have initiator.
> >>>> Is it valid to have mixed configuration?
> >>>> Should we forbid it?
> >>>
> >>> The spec talks about the "Proximity Domain for the Attached Initiator"
> >>> field only being valid if the memory controller for the memory can be
> >>> identified by an initiator id in the SRAT. So I expect the only way to
> >>> define a memory proximity domain without this local initiator is to
> >>> allow specifying a node-id that does not have an entry in the SRAT.
> >>>
> >> Hi Dan,
> >>
> >> So there may be a situation for the Attached Initiator field is not
> >> valid? If true, I would allow user to input Initiator invalid.
> >
> > Yes it's something the OS needs to consider because the platform may
> > not be able to meet the constraint that a single initiator is
> > associated with the memory controller for a given memory target. In
> > retrospect it would have been nice if the spec reserved 0xffffffff for
> > this purpose, but it seems "not in SRAT" is the only way to identify
> > memory that is not attached to any single initiator.
> >
> But As far as I konw, QEMU can't emulate a NUMA node "not in SRAT". I am
> wondering if it is effective only set Initiator invalid?

You don't need to emulate a NUMA node not in SRAT. Just put a number
in this HMAT entry larger than the largest proximity domain number
found in the SRAT.
>