RE: [PATCH v3 28/28] xen/domctl: wrap common/domctl.c with CONFIG_MGMT_HYPERCALLS

["Penny, Zheng" <penny.zheng@xxxxxxx>]

[Public]

> -----Original Message-----
> From: Jan Beulich <jbeulich@xxxxxxxx>
> Sent: Tuesday, November 18, 2025 3:14 PM
> To: Penny, Zheng <penny.zheng@xxxxxxx>
> Cc: Huang, Ray <Ray.Huang@xxxxxxx>; oleksii.kurochko@xxxxxxxxx; Andrew
> Cooper <andrew.cooper3@xxxxxxxxxx>; Anthony PERARD
> <anthony.perard@xxxxxxxxxx>; Orzel, Michal <Michal.Orzel@xxxxxxx>; Julien
> Grall <julien@xxxxxxx>; Roger Pau Monné <roger.pau@xxxxxxxxxx>; Stefano
> Stabellini <sstabellini@xxxxxxxxxx>; xen-devel@xxxxxxxxxxxxxxxxxxxx
> Subject: Re: [PATCH v3 28/28] xen/domctl: wrap common/domctl.c with
> CONFIG_MGMT_HYPERCALLS
>
> On 18.11.2025 07:43, Penny, Zheng wrote:
> > [Public]
> >
> >> -----Original Message-----
> >> From: Jan Beulich <jbeulich@xxxxxxxx>
> >> Sent: Thursday, October 30, 2025 9:40 PM
> >> To: Penny, Zheng <penny.zheng@xxxxxxx>
> >> Cc: Huang, Ray <Ray.Huang@xxxxxxx>; oleksii.kurochko@xxxxxxxxx;
> >> Andrew Cooper <andrew.cooper3@xxxxxxxxxx>; Anthony PERARD
> >> <anthony.perard@xxxxxxxxxx>; Orzel, Michal <Michal.Orzel@xxxxxxx>;
> >> Julien Grall <julien@xxxxxxx>; Roger Pau Monné
> >> <roger.pau@xxxxxxxxxx>; Stefano Stabellini <sstabellini@xxxxxxxxxx>;
> >> xen-devel@xxxxxxxxxxxxxxxxxxxx
> >> Subject: Re: [PATCH v3 28/28] xen/domctl: wrap common/domctl.c with
> >> CONFIG_MGMT_HYPERCALLS
> >>
> >> On 13.10.2025 12:15, Penny Zheng wrote:
> >>> --- a/xen/common/Kconfig
> >>> +++ b/xen/common/Kconfig
> >>> @@ -646,11 +646,13 @@ config SYSTEM_SUSPEND
> >>>       If unsure, say N.
> >>>
> >>>  config MGMT_HYPERCALLS
> >>> -   def_bool y
> >>> +   bool "Enable privileged hypercalls for system management"
> >>>     help
> >>>       This option shall only be disabled on some dom0less systems, or
> >>>       PV shim on x86, to reduce Xen footprint via managing unnessary
> >>> -     hypercalls, like sysctl, etc.
> >>> +     hypercalls, like sysctl, domctl, etc.
> >>> +     Be cautious to disable it, as users will face missing a few basic
> >>> +     hypercalls like listdomains, getdomaininfo, etc.
> >>
> >> This is still too little, imo. For one I'm not sure "users" is quite
> >> the right term. I'd say it's more "admins". And then, as mentioned,
> >> there are a few domctl-s which are usable by DMs. Aiui device
> >> pass-through may also be impacted, which imo will want mentioning
> >> here as well. Or else, if there is an implication that DMs aren't to be 
> >> used when
> MGMT_HYPERCALLS=n, that is what would want calling out.
> >
> > How about
> > "
> >         Be cautious to disable it, as admins will face missing a few basic
> >         hypercalls like listdomains, getdomaininfo, etc, hence leading to
> >         have an impact on xl-device-passthrough and restricted DM.
> > "
>
> Much better. However, why "xl-" and why "restricted"? Neither aspect matters 
> here,
> unless I overlook something.
>

Later, in hyperlaunch scenario, device passthrough is still needed, but it's 
not current device passthrough mode, which depends on xl-tool-stack to 
de-assign it from hardware domain and re-assign it to guest. It will be limited 
in boot-up stage, and configured via device tree only. FWIU, we may reuse VPCI 
framework, but commands like "xl assign/deassign xxx" will not be needed 
anymore. PLZ correct me if understand wrongly, @Andryuk, Jason

And DM, like QEMU, is still applicable, but only supports a new machine type, 
"pvh".

If it is too much details and only brings confusion, I'll delete and refine it 
to " have an impact on device-passthrough and DM "

> > Another question on PV_SHIM_EXCLUSIVE:
> > After Stefano's " 6c80f0dd1bb  xen: fix randconfig build problems after 
> > introducing
> SYSCTL " reversion patch, and to avoid incurring randconfig failures till the 
> last,
> maybe I shall combine all PV_SHIM_EXCLUSIVE-related changes into a new
> commit and put it in the last, after making MGMT_HYPERCALLS optional again?
>
> Whatever works best.
>
> Jan