On 06.09.21 17:47, Jan Beulich wrote: > On 03.09.2021 12:08, Oleksandr Andrushchenko wrote: >> From: Oleksandr Andrushchenko <oleksandr_andrushche...@epam.com> >> >> Instead of handling a single range set, that contains all the memory >> regions of all the BARs and ROM, have them per BAR. > Without looking at how you carry out this change - this look wrong (as > in: wasteful) to me. Despite ... > >> This is in preparation of making non-identity mappings in p2m for the >> MMIOs/ROM. > ... the need for this, every individual BAR is still contiguous in both > host and guest address spaces, so can be represented as a single > (start,end) tuple (or a pair thereof, to account for both host and guest > values). No need to use a rangeset for this.
First of all this change is in preparation for non-identity mappings, e.g. currently we collect all the memory ranges which require mappings into a single range set, then we cut off MSI-X regions and then use range set functionality to call a callback for every memory range left after MSI-X. This works perfectly fine for 1:1 mappings, e.g. what we have as the range set's starting address is what we want to be mapped/unmapped. Why range sets? Because they allow partial mappings, e.g. you can map part of the range and return back and continue from where you stopped. And if I understand that correctly that was the initial intention of introducing range sets here. For non-identity mappings this becomes not that easy. Each individual BAR may be mapped differently according to what guest OS has programmed as bar->guest_addr (guest view of the BAR start). Thus we need to collect all those non-identity mappings per BAR now (so we have a mapping "guest view" : "physical BAR" and again cut off MSI-X regions as before. So, yes, it may be a bit wasteful to use many range sets, but makes vPCI life much-much easier. Thus, I think that even per-BAR range sets are good to go as they have more pros than cons. IMO Even if we go with "can be represented as a single (start,end) tuple" it doesn't answer the question what needs to be done if a range gets partially mapped/unmapped. We'll need to put some logic to re-try the operation later and remember where did we stop. At the end of the day we'll invent one more range set, but now vPCI own. > > Jan > Thank you, Oleksandr
