Re: [Xen-devel] [PATCH v2 1/2] altp2m: Merge p2m_set_altp2m_mem_access and p2m_set_mem_access

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

On Mon, 2016-02-01 at 09:21 -0700, Jan Beulich wrote:
> > > > On 01.02.16 at 15:45, <ian.campbell@xxxxxxxxxx> wrote:
> > On Fri, 2016-01-29 at 09:47 -0700, Jan Beulich wrote:
> > > > > > On 29.01.16 at 17:32, <tlengyel@xxxxxxxxxxx> wrote:
> > > > On Fri, Jan 29, 2016 at 9:19 AM, Jan Beulich <JBeulich@xxxxxxxx>
> > > > wrote:
> > > > > > > > On 29.01.16 at 17:12, <tlengyel@xxxxxxxxxxx> wrote:
> > > > > > On Fri, Jan 29, 2016 at 4:03 AM, Jan Beulich <JBeulich@xxxxxxxx
> > > > > > >
> > > > > > wrote:
> > > > > > > > > > On 28.01.16 at 21:58, <tlengyel@xxxxxxxxxxx> wrote:
> > > > > > > > --- a/xen/include/public/memory.h
> > > > > > > > +++ b/xen/include/public/memory.h
> > > > > > > > @@ -423,11 +423,14 @@ struct xen_mem_access_op {
> > > > > > > > ÂÂÂÂÂ/* xenmem_access_t */
> > > > > > > > ÂÂÂÂÂuint8_t access;
> > > > > > > > ÂÂÂÂÂdomid_t domid;
> > > > > > > > +ÂÂÂÂuint16_t altp2m_idx;
> > > > > > > > +ÂÂÂÂuint16_t _pad;
> > > > > > > > ÂÂÂÂÂ/*
> > > > > > > > ÂÂÂÂÂÂ* Number of pages for set op
> > > > > > > > ÂÂÂÂÂÂ* Ignored on setting default access and other ops
> > > > > > > > ÂÂÂÂÂÂ*/
> > > > > > > > ÂÂÂÂÂuint32_t nr;
> > > > > > > > +ÂÂÂÂuint32_t _pad2;
> > > > > > > 
> > > > > > > Repeating what I had said on v1: So this is a tools only
> > > > > > > interface,
> > > > > > > yes. But it's not versioned (other than e.g. domctl and
> > > > > > > sysctl),
> > > > > > > so
> > > > > > > altering the interface structure is at least fragile.
> > > > > > 
> > > > > > Not sure what I can do to address this.
> > > > > 
> > > > > Deprecate the old interface and introduce a new one. But other
> > > > > maintainers' opinions would be welcome.
> > > > 
> > > > That seems like a very heavy handed solution to me.
> > > 
> > > I understand that - hence the request for others' opinions.
> > 
> > It's unfortunate that we've found ourselves here, but I think rather
> > than
> > deprecating the current and adding a new op alongside we should just
> > accept
> > the one-time fragility this time around, add the version field as part
> > of
> > this set of changes and try and remember to include a version number
> > for
> > next time we add a tools only interface. I don't think xenaccess is yet
> > widely used outside of Tamas and the Bitdfender folks, who I would
> > assume
> > can cope with such a change.
> > 
> > I could accept changing the op number would make sense, but I don't
> > think
> > we should deprecate the old one (which implies continuing to support it
> > in
> > parallel), if we go this route we should just retire the old number to
> > straight away to return -ENOSYS (or maybe -EACCESS, which is what a
> > version
> > mismatch would have resulted in).
> 
> That actually looks like a reasonable compromise, until we finally
> manage to get around to morph the tools-only HVM-ops into a
> new hvmctl hypercall (leaving only guest accessible ones in the
> current interface).

Aren't the ones being discussed here xenmem subops rather than hvmops?

Ian.

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