Re: [PATCH 14/22] x86/domain_page: remove the fast paths when mfn is not in the directmap

[Elias El Yandouzi <eliasely@xxxxxxxxxx>]

Hi Jan,

On 11/01/2023 14:11, Jan Beulich wrote:
> As to using pmap - assuming you've done an audit and the number of
> simultaneous mappings that can be in use can be proven to not exceed
> the number of slots available, can you please say so in the description?
I don't know if any audit has been made but a similar code has been 
internally used for a few years now without any problem.
Quickly looking at the slots usage, I found that at most only 4 slots 
out of 8 would be used during boot time.
> I have to admit though that I'm wary - this isn't a per-CPU number of
> slots aiui, but a global one. But then you also have a BUG_ON() there
> restricting the use to early boot. The reasoning for this is also
> missing (and might address my concern).

Indeed, this isn't presented as a per-CPU number of slots, but the slots 
can be only used before we reach the state SYS_STATE_smp_boot. So 
effectively, only the BSP would use the PMAP slots.
The PMAP slots are meant to map at most the number of level page-tables.
See the comment on top of NUM_FIX_PMAP definition.

--
Elias