Re: [PATCH 5/5] vtd: Move intremap table to xenheap
Teddy Astie <[email protected]>
| Newsgroups | org.xenproject.lists.xen-devel |
|---|---|
| Message-ID | <1785933773.8631fc262581453bbf619ec5b2062170.19fd1f2bc52000e099@vates.tech> |
Le 05/08/2026 à 12:09, Andrew Cooper a écrit : > On 05/08/2026 10:44 am, Jan Beulich wrote: >> On 29.07.2026 11:59, Teddy Astie wrote: >>> Interrupt remapping entries often needs to be accessed, and we're creating >>> pointers to it on demand, which brings a lot of complexity (e.g >>> GET_IREMAP_ENTRY() macro), move it to xenheap such that it's persistently >>> mapped and we won't have to worry about mapping and unmapping individual >>> intremap table pages. >> Afaic: No movement from domheap to xenheap except for _very_ good reasons. >> For the case here that is - maybe establish a permanent mapping using >> vmap(), but no change in where the memory is to come from. Whether such a >> permanent mapping is really worthwhile may also want supporting by numbers. >> You say "often", but you don't qualify / quantify this any further. > I think the reduction the complexity of the logic is a good reason into using a persistent mapping here (especially since it's not a particularly large one). > To expand on the "why" a bit more. > > For systems with all RAM below the 4T boundary, domheap and xenheap are > equivalent. We have 5T of directmap, but xenheap allocations have a > width restriction which is a power-of-2. > > For systems with any RAM above the 4T boundary, you can't have xenheap > allocations be NUMA-local for all NUMA nodes. > > > As for "often", the IRTEs are modified every time a vCPU moves to a > different PCPU, because the target addresses need updating. While it > probably doesn't matter much today, in the context of ASI it's something > which would want mapping permanently, rather than on-demand. > Ok, so domheap with vmap would be preferable here. > ~Andrew> Teddy
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