Re: [PATCH v2 07/14] x86/mm: simplify create_perdomain_mapping() interface

[Jan Beulich <jbeulich@xxxxxxxx>]

On 02.09.2026 11:43, George Dunlap wrote:
> From: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> 
> create_perdomain_mapping()'s interface is richer than any caller needs.
> The paging structure for the requested range is built to a depth
> selected by the pl1tab and ppg arguments, each of which distinguishes
> NULL from NIL() from a real pointer:
> 
>  - nr == 0: only ensure the per-domain L3 exists; nothing else is
>    allocated, and the other arguments are ignored.
>  - pl1tab == a pointer: allocate the L1 tables covering the range from
>    the *xenheap*, and return their (stable, direct-map) addresses in
>    the array -- the mode that existed to build the GDT/LDT stash.
>  - pl1tab == NIL(): allocate the L1 tables from the domain heap, and
>    return nothing.
>  - pl1tab == NULL: do not plumb L1 tables for their own sake (they are
>    still allocated on demand if data-page population requires them).
>  - ppg == a pointer: allocate and install zeroed data pages across the
>    range, and return their struct page_info pointers in the array.
>  - ppg == NIL(): allocate and install the zeroed data pages, but hand
>    nothing back; the pages are reachable only through the mapping.
>  - ppg == NULL: do not allocate data pages.
>  - both NULL, nr > 0: stop after the slot's L2; do not plumb L1 tables
>    at all.
> 
> Very few of these modes have users now.  The last user of the
> pl1tab capture mode was removed when we removed the GDT/LDT stash.
> The ppg capture mode never had any users.  Nothing uses the both-NULL
> L2-only mode with nr != 0.  What remains is exactly one bit of
> information: whether the caller wants the range populated with zeroed,
> area-owned data pages, or merely plumbed down to the L1 tables, ready
> for populate_perdomain_mapping() to install caller-owned pages.
> 
> Replace the two arguments with a boolean expressing that bit.  With the
> stashing mode gone the NIL()/IS_NIL() macros lose their last user, so
> drop them as well; and document the resulting interface.
> 
> No caller changes behaviour: every existing call maps onto the boolean
> exactly.
> 
> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> Assisted-by: Claude Code:claude-fable-5
> Signed-off-by: George Dunlap <gwd@xxxxxxxxxxxxxx>

Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>