Re: [PATCH] xen/x86: move domctl.o out of PV_SHIM_EXCLUSIVE

[Jan Beulich <jbeulich@xxxxxxxx>]

On 27.08.2025 02:33, Stefano Stabellini wrote:
> So I ran a test and the appended change, which is based on [1] and
> renaming CONFIG_DOMCTL to CONFIG_SYSCTL, is sufficient to resolve the
> build issue.
> 
> For 4.21, I suggest we go with two patches:
> 1) global rename of CONFIG_SYSCTL to CONFIG_MGMT_HYPERCALLS
> 2) stub domctl_lock_acquire/release based on CONFIG_MGMT_HYPERCALLS
> 
> Jan, are you OK with this?

Naming if the option aside, no, I fear I dislike the stubbing. What's
worse though, ...

> --- a/xen/include/xen/domain.h
> +++ b/xen/include/xen/domain.h
> @@ -148,8 +148,17 @@ void arch_dump_domain_info(struct domain *d);
>  
>  int arch_vcpu_reset(struct vcpu *v);
>  
> +#ifdef CONFIG_SYSCTL
>  bool domctl_lock_acquire(void);
>  void domctl_lock_release(void);
> +#else
> +static inline bool domctl_lock_acquire(void)
> +{
> +    return false;

... this will break x86'es HVM_PARAM_IDENT_PT handling. That is, in
principle I would agree that returning false here is appropriate. But
for the specific case there it's wrong.

As said on the call yesterday, until what you call MGMT_HYPERCALLS is
completely done, the option needs to be prompt-less, always-on. Adding
a prompt was necessary to be the last thing on the SYSCTL series, and
it'll need to be last on the follow-on one masking out further
hypercalls. IOW my take is that 34317c508294 and 568f806cba4c will
need reverting (the latter being what caused the regression, and the
former depending on the latter), to allow to cleanly continue that
work after the rename. If we don't do the reverts now (and take either
Penny's patch or what you propose), imo we'll need to do them later.
Else we're risking to introduce new randconfig breakages while the
further conversion work is ongoing.

Jan