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Re: [PATCH 01/10] x86/mm: no-one passes a NULL domain to init_xen_l4_slots()

On 17/04/2020 15:25, Jan Beulich wrote:
> Drop the NULL checks - they've been introduced by commit 8d7b633ada
> ("x86/mm: Consolidate all Xen L4 slot writing into
> init_xen_l4_slots()") for no apparent reason.

:) I'll take this as conformation that all my sudden pagetable work in
Xen manage ended up being rather more subtle than Linux's equivalent
work for KPTI.


Specifically, this was part of trying to arrange for fully per-pcpu
private mappings, and was used to construct the pagetables for the idle
vcpu which specifically don't have a perdomain mapping.

Seeing as this is still an outstanding task in the secret-free-Xen
plans, any dropping of it now will have to be undone at some point in
the future.  Is there a specific reason for the cleanup?

> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> --- a/xen/arch/x86/mm.c
> +++ b/xen/arch/x86/mm.c
> @@ -1696,7 +1696,7 @@ void init_xen_l4_slots(l4_pgentry_t *l4t

If we continue with this patch, this comment, just out of context, needs


>       * PV vcpus need a shortened directmap.  HVM and Idle vcpus get the full
>       * directmap.
>       */
> -    bool short_directmap = d && !paging_mode_external(d);
> +    bool short_directmap = !paging_mode_external(d);
>      /* Slot 256: RO M2P (if applicable). */
>      l4t[l4_table_offset(RO_MPT_VIRT_START)] =



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