Re: [XEN PATCH v4 12/14] x86/ioreq: guard VIO_realmode_completion with CONFIG_VMX

[Sergiy Kibrik <sergiy_kibrik@xxxxxxxx>]

09.07.24 10:28, Jan Beulich:
> On 09.07.2024 08:09, Sergiy Kibrik wrote:
> > --- a/xen/arch/x86/include/asm/hvm/ioreq.h
> > +++ b/xen/arch/x86/include/asm/hvm/ioreq.h
> > @@ -13,6 +13,11 @@
> >   #define IOREQ_STATUS_UNHANDLED   X86EMUL_UNHANDLEABLE
> >   #define IOREQ_STATUS_RETRY       X86EMUL_RETRY
> >   
> > +#ifdef CONFIG_VMX
> > +bool arch_vcpu_ioreq_completion(enum vio_completion completion);
> > +#define arch_vcpu_ioreq_completion
> > +#endif
> Putting the (or some kind of) #define here is certainly fine, but moving ...
>
> > --- a/xen/include/xen/ioreq.h
> > +++ b/xen/include/xen/ioreq.h
> > @@ -111,7 +111,6 @@ void ioreq_domain_init(struct domain *d);
> >   int ioreq_server_dm_op(struct xen_dm_op *op, struct domain *d, bool 
> > *const_op);
> >   
> >   bool arch_ioreq_complete_mmio(void);
> > -bool arch_vcpu_ioreq_completion(enum vio_completion completion);
> >   int arch_ioreq_server_map_pages(struct ioreq_server *s);
> >   void arch_ioreq_server_unmap_pages(struct ioreq_server *s);
> >   void arch_ioreq_server_enable(struct ioreq_server *s);
> ... the declaration from here requires that all architectures wanting to
> implement the function need to have identical copies. That's unnecessary
> risk of going out of sync.
>
> As to the #define itself: It expanding to nothing means the call site
> de-generates to
>
> #ifdef arch_vcpu_ioreq_completion
>          res = (completion);
> #else
>
> which hardly is what is meant (despite compiling fine, and it likely
> only being Eclair which would then tell us about the issue). Further
> there you're also removing a blank line, I don't see why you're doing
> that.
looking through these changes once again I wonder why can't we just move 
stub to the header like this:
in xen/include/xen/ioreq.h:

#ifdef arch_vcpu_ioreq_completion

#ifdef CONFIG_VMX
bool arch_vcpu_ioreq_completion(enum vio_completion completion);
#else
static inline bool arch_vcpu_ioreq_completion(enum vio_completion 
completion)
{
    ASSERT_UNREACHABLE();
    return true;
}
#endif


and avoid additional pre-processor variables & conditionals, because it 
looks like we do need some kind of stub that does ASSERT_UNREACHABLE() 
anyway.
  -Sergiy