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

On 20/04/2020 06:48, Jan Beulich wrote:
> 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.


The only reason we don't need it right now is because idle_pg_table[]
gets constructed at boot time.  As soon as we're creating one (or more)
per pcpu, we need a way of writing an L4 without a perdomain mapping.




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