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

[Jan Beulich <jbeulich@xxxxxxxx>]

On 17.04.2020 21:46, Andrew Cooper wrote:
> 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.
> 
> https://lists.xenproject.org/archives/html/xen-devel/2018-01/msg00281.html
> 
> 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.

s/will/may/ I suppose - we don't know for sure how this will look
like at this point.

>  Is there a specific reason for the cleanup?

Elimination of effectively dead code. We avoid arbitrary NULL checks
elsewhere as well; iirc I've seen you (amongst others) comment on
people trying to introduce such in their patches.

>> 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
> adjusting.

Will do.

Jan