Re: [PATCH v2 08/14] x86/mm: purge unneeded destroy_perdomain_mapping()

[Jan Beulich <jbeulich@suse.com>]

On 02.09.2026 11:43, George Dunlap wrote:
> From: Roger Pau Monné <roger.pau@citrix.com>
> 
> We want to change per-domain mappings to be per-vCPU mappings.  In
> preparation for that, we want to arrange that
> destroy_perdomain_mapping() work either with a single perdomain area,
> or with a per-vCPU perdomain area.
> 
> There are two calls made from domain-scoped contexts; both calls turn
> out to be unnecessary:
> 
> - destroy_perdomain_mapping() is not logically the undo of
>   create_perdomain_mapping(), as the name and its use in
>   hvm_domain_initialise() suggest.  create_ allocates a per-domain L3,
>   but destroy_ tears down mappings without freeing it; and since the
>   call here passes nr == 0, it tears down nothing at all.  The
>   per-domain L3 page is actually freed by free_perdomain_mappings(),
>   which hvm_domain_initialise()'s caller, arch_domain_create(),
>   already invokes on its failure path.
> 
> - The call in pv_domain_destroy() is redundant: arch_domain_destroy()
>   unconditionally calls free_perdomain_mappings(), which tears down
>   the same entries and additionally frees the page-table structures.

pv_domain_destroy() has a 2nd call site (the error path of
pv_domain_initialise()), but the situation is the same there:
arch_domain_create()'s error path also calls free_perdomain_mappings().

> Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
> Reviewed-by: Alejandro Vallejo <alejandro.vallejo@cloud.com>
> Assisted-by: Claude Code:claude-fable-5
> Signed-off-by: George Dunlap <gwd@xenproject.org>

With the description amended:
Reviewed-by: Jan Beulich <jbeulich@suse.com>

Jan