Re: [PATCH v2 18/26] xen/domctl: wrap xsm_getdomaininfo() with CONFIG_MGMT_HYPERCALLS

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Sun, 28 Sep 2025, Jan Beulich wrote:
> On 26.09.2025 21:24, Stefano Stabellini wrote:
> > On Thu, 25 Sep 2025, Penny, Zheng wrote:
> >>> -----Original Message-----
> >>> From: Jan Beulich <jbeulich@xxxxxxxx>
> >>> Sent: Friday, September 26, 2025 2:53 PM
> >>> To: Penny, Zheng <penny.zheng@xxxxxxx>
> >>> Cc: Huang, Ray <Ray.Huang@xxxxxxx>; Daniel P. Smith
> >>> <dpsmith@xxxxxxxxxxxxxxxxxxxx>; xen-devel@xxxxxxxxxxxxxxxxxxxx; 
> >>> Stabellini,
> >>> Stefano <stefano.stabellini@xxxxxxx>; Andryuk, Jason
> >>> <Jason.Andryuk@xxxxxxx>
> >>> Subject: Re: [PATCH v2 18/26] xen/domctl: wrap xsm_getdomaininfo() with
> >>> CONFIG_MGMT_HYPERCALLS
> >>>
> >>> On 26.09.2025 06:41, Penny, Zheng wrote:
> >>>>> -----Original Message-----
> >>>>> From: Jan Beulich <jbeulich@xxxxxxxx>
> >>>>> Sent: Thursday, September 25, 2025 10:29 PM
> >>>>>
> >>>>> On 25.09.2025 11:41, Penny, Zheng wrote:
> >>>>>>> -----Original Message-----
> >>>>>>> From: Jan Beulich <jbeulich@xxxxxxxx>
> >>>>>>> Sent: Thursday, September 11, 2025 9:30 PM
> >>>>>>>
> >>>>>>> On 10.09.2025 09:38, Penny Zheng wrote:
> >>>>>>>> --- a/xen/include/xsm/xsm.h
> >>>>>>>> +++ b/xen/include/xsm/xsm.h
> >>>>>>>> @@ -55,8 +55,8 @@ struct xsm_ops {
> >>>>>>>>      void (*security_domaininfo)(struct domain *d,
> >>>>>>>>                                  struct xen_domctl_getdomaininfo 
> >>>>>>>> *info);
> >>>>>>>>      int (*domain_create)(struct domain *d, uint32_t ssidref);
> >>>>>>>> -    int (*getdomaininfo)(struct domain *d);
> >>>>>>>>  #ifdef CONFIG_MGMT_HYPERCALLS
> >>>>>>>> +    int (*getdomaininfo)(struct domain *d);
> >>>>>>>>      int (*domctl_scheduler_op)(struct domain *d, int op);
> >>>>>>>>      int (*sysctl_scheduler_op)(int op);
> >>>>>>>>      int (*set_target)(struct domain *d, struct domain *e); @@
> >>>>>>>> -234,7
> >>>>>>>> +234,11 @@ static inline int xsm_domain_create(
> >>>>>>>>
> >>>>>>>>  static inline int xsm_getdomaininfo(xsm_default_t def, struct
> >>>>>>>> domain
> >>>>>>>> *d)  {
> >>>>>>>> +#ifdef CONFIG_MGMT_HYPERCALLS
> >>>>>>>>      return alternative_call(xsm_ops.getdomaininfo, d);
> >>>>>>>> +#else
> >>>>>>>> +    return -EOPNOTSUPP;
> >>>>>>>> +#endif
> >>>>>>>>  }
> >>>>>>>
> >>>>>>> This is in use by a Xenstore sysctl and a Xenstore domctl. The
> >>>>>>> sysctl is hence already broken with the earlier series. Now the
> >>>>>>> domctl is also being screwed up. I don't think MGMT_HYPERCALLS
> >>>>>>> really ought to extend to any operations available to other than the 
> >>>>>>> core
> >>> toolstack.
> >>>>>>> That's the Xenstore ones here, but also the ones used by qemu
> >>>>>>> (whether run in
> >>>>> Dom0 or a stubdom).
> >>>>>>
> >>>>>> Maybe not only limited to the core toolstack. In
> >>>>>> dom0less/hyperlaunched
> >>>>> scenarios, hypercalls are strictly limited. QEMU is also limited to
> >>>>> pvh machine type and with very restricted functionality(, only acting
> >>>>> as a few virtio-pci devices backend). @Andryuk, Jason @Stabellini,
> >>>>> Stefano Am I understanding correctly and thoroughly about our scenario 
> >>>>> here for
> >>> upstream?
> >>>>>> Tracking the codes, if Xenstore is created as a stub domain, it
> >>>>>> requires
> >>>>> getdomaininfo-domctl to acquire related info.  Sorry, I haven't found
> >>>>> how it was called in QEMU...
> >>>>>
> >>>>> It's not "it"; it's different ones. First and foremost I was thinking
> >>>>> of
> >>>>>  * XEN_DOMCTL_ioport_mapping
> >>>>>  * XEN_DOMCTL_memory_mapping
> >>>>>  * XEN_DOMCTL_bind_pt_irq
> >>>>>  * XEN_DOMCTL_unbind_pt_irq
> >>>>> but there may be others (albeit per the dummy xsm_domctl() this is
> >>>>> the full set). As a general criteria, anything using XSM_DM_PRIV
> >>>>> checking can in principle be called by qemu.
> >>>>>
> >>>>
> >>>> Understood.
> >>>> I assume that they are all for device passthrough. We are not accepting 
> >>>> device
> >>> passthrough via core toolstack in dom0less/hyperlaunch-ed scenarios. 
> >>> Jason has
> >>> developed device passthrough through device tree to only accept "static
> >>> configured" passthrough in dom0less/hyperlaunch-ed scenario, while it is 
> >>> still
> >>> internal , it may be the only accept way to do device passthrough in
> >>> dom0less/hyperlaunch-ed scenario.
> >>>
> >>> Right, but no matter what your goals, the upstream contributions need to 
> >>> be self-
> >>> consistent. I.e. not (risk to) break other functionality. (Really the 
> >>> four domctl-s
> >>> mentioned above might better have been put elsewhere, e.g. as dm-ops. 
> >>> Moving
> >>> them may be an option here.)
> >>
> >> Understood.
> >> I'll move them all to the dm-ops
> > 
> > Hi Penny, Jan, I advise against this.
> > 
> > I think it is clear that there are open questions on how to deal with
> > the safety scenarios. I briefly mentioned some of the issues last week
> > at Xen Summit. One example is the listdomains hypercall that should be
> > available to the control domain. We cannot resolve all problems with
> > this patch series. I think we should follow a simpler plan:
> > 
> > 1) introduce CONFIG_MGMT_HYPERCALLS the way this patch series does,
> >    removing all domctls and sysctls
> > 
> > 2) make further adjustments, such as making available the listdomains
> >    hypercall and/or the hypercalls listed by Jan as a second step after
> >    it
> 
> I'm going to be okay-ish with that as long as the help text of the Kconfig
> option clearly mentions those extra pitfalls.

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