Re: [PATCH v3 02/18] x86/mm: purge unneeded destroy_perdomain_mapping()

[Roger Pau Monné <roger@xxxxxxxxxxxxxx>]

On Thu, Oct 08, 2026 at 09:55:46AM +0200, Jan Beulich wrote:
> On 07.10.2026 12:40, George Dunlap wrote:
> > --- a/xen/arch/x86/x86_64/mm.c
> > +++ b/xen/arch/x86/x86_64/mm.c
> > @@ -737,6 +737,11 @@ int setup_compat_arg_xlat(struct vcpu *v)
> >                                      NULL, NIL(struct page_info *));
> >  }
> >  
> > +/*
> > + * Besides vCPU teardown, which free_perdomain_mappings() would cover, this
> > + * serves switch_compat()'s undo path: the domain lives on as a 64-bit one
> > + * there, so the translation area has to go right away.
> > + */
> 
> Is it really "has to"? The xlat area is simply unused for 64-bit guests,
> so it would be merely "needlessly occupying resources" if we deferred
> freeing until domain destruction.

I wondered the same, but pv_vcpu_destroy() won't free the xlat are if
is_pv_32bit_vcpu() returns false, which would be the case if
switch_compat() fails.  All this could be adjusted, but it seemed more
churn than benefit.

Roger.