Re: [Xen-devel] [PATCH for-4.6 v2 2/3] xl: error out if vNUMA specifies more vcpus than pcpus

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

On Fri, 2015-08-14 at 00:38 +0100, Wei Liu wrote:
> > In fact, if b_info->max_vcpus is 0, the elements of vcpu_parsed are
> > sized against the host pcpus, and we risk to call libxl_bitmap_set() for
> > vcpus beyond that limit, while parsing the "vcpus" subsection of the
> > vnode specification (which happens _before_ this check).
> > 
> > Or am I missing something?
> > 
> 
> That's fine because that function has no effect when you try to set a
> bit beyond its size.

This sort of subtlety is worthy of a comment in either the code of the
commit message.

> > Assuming I'm not, it seems to me that a solution could be to check for
> > this situation _inside_ the 'else if (!strcmp("vcpus", option))'. In
> > fact, if "maxvcpus" has not been specified, as soon as the end of one of
> > the ranges --as returned by parse_range()-- is beyond host_cpus, we know
> > we'd be going past the limit of the corresponding element of
> > vcpu_parsed, and we can error out.

FWIW that's what I was expecting to happen...

> > It'll most likely be a bit uglier than this patch, but probably still
> > less complex than v1. :-)

> That doesn't make any difference in terms of functionality. I would
> rather leave the parsing bit as it is and deal with fallout 
> separately.
> That would make code cleaner IMHO.

... It's a bit wasteful to keep parsing after things have already
failed, but I suppose that's not too bad and we can live with it.

Ian

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