Re: [PATCH] x86/mm: limit deferred TLB flushing to PV owned pages

[Jan Beulich <jbeulich@suse.com>]

On 09.09.2026 09:24, Roger Pau Monne wrote:
> The current logic on x86 will mark all domain owned pages as needed a TLB
> flush before being re-used.  However such TLB flushing is only strictly
> needed for PV domain owned pages, as those can keep a reference to the page
> in the TLB after it has been freed.

What about HVM-owned ones which a PV domain has grant- or foreign-mapped?

> --- a/xen/common/page_alloc.c
> +++ b/xen/common/page_alloc.c
> @@ -1501,6 +1501,7 @@ bool scrub_free_pages(void)
>  
>  static bool mark_page_free(struct page_info *pg, mfn_t mfn)
>  {
> +    const struct domain *owner = page_get_owner(pg);
>      bool pg_offlined = false;
>  
>      ASSERT(mfn_x(mfn) == mfn_x(page_to_mfn(pg)));
> @@ -1539,7 +1540,7 @@ static bool mark_page_free(struct page_info *pg, mfn_t mfn)
>      }
>  
>      /* If a page has no owner it will need no safety TLB flush. */
> -    pg->u.free.need_tlbflush = (page_get_owner(pg) != NULL);
> +    pg->u.free.need_tlbflush = owner && is_pv_domain(owner);
>      if ( pg->u.free.need_tlbflush )
>          page_set_tlbflush_timestamp(pg);

Imo whichever change it is going to be here, it definitely also requires
the comment to be kept in sync.

Jan