With there being a way to disable v2 support, telling new guests to use
v2 exclusively is not a good suggestion.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Luca Fancellu <luca.fancellu@arm.com>
---
v2: s/be able to fall back/default/.

--- a/xen/include/public/grant_table.h
+++ b/xen/include/public/grant_table.h
@@ -121,8 +121,9 @@ typedef uint32_t grant_ref_t;
  */
 
 /*
- * Version 1 of the grant table entry structure is maintained purely
- * for backwards compatibility.  New guests should use version 2.
+ * Version 1 of the grant table entry structure is maintained largely for
+ * backwards compatibility.  New guests are recommended to support using
+ * version 2 to overcome version 1 limitations, but to default to version 1.
  */
 #if __XEN_INTERFACE_VERSION__ < 0x0003020a
 #define grant_entry_v1 grant_entry

Jan Beulich writes ("[PATCH v2] public/gnttab: relax v2 recommendation"):
> With there being a way to disable v2 support, telling new guests to use
> v2 exclusively is not a good suggestion.
> 
> Signed-off-by: Jan Beulich <jbeulich@suse.com>
> Reviewed-by: Luca Fancellu <luca.fancellu@arm.com>

Release-Acked-by: Ian Jackson <iwj@xenproject.org>

This is a just a comment change and AIUI the recommendation ought to
be the same for all relevant versions.

We should consider backporting too.

Ian.

On 15.11.2021 10:55, Jan Beulich wrote:
> With there being a way to disable v2 support, telling new guests to use
> v2 exclusively is not a good suggestion.
> 
> Signed-off-by: Jan Beulich <jbeulich@suse.com>
> Reviewed-by: Luca Fancellu <luca.fancellu@arm.com>
> ---
> v2: s/be able to fall back/default/.
> 
> --- a/xen/include/public/grant_table.h
> +++ b/xen/include/public/grant_table.h
> @@ -121,8 +121,9 @@ typedef uint32_t grant_ref_t;
>   */
>  
>  /*
> - * Version 1 of the grant table entry structure is maintained purely
> - * for backwards compatibility.  New guests should use version 2.
> + * Version 1 of the grant table entry structure is maintained largely for
> + * backwards compatibility.  New guests are recommended to support using
> + * version 2 to overcome version 1 limitations, but to default to version 1.
>   */
>  #if __XEN_INTERFACE_VERSION__ < 0x0003020a
>  #define grant_entry_v1 grant_entry

This being a comment only change (and hence close to zero risk) I wonder
whether this wouldn't still be appropriate for 4.16. I'm sorry for not
having remembered earlier to submit v2 of this.

Jan