Re: [PATCH 5/5] vtd: Move intremap table to xenheap

Teddy Astie <[email protected]> Wed, 5 Aug 2026 14:42:52 +0200

Newsgroups	gmane.comp.emulators.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

OpenPGP_0x660FA9D102CBCFD0.asc (application/pgp-keys, 2.4 KB)

-----BEGIN PGP PUBLIC KEY BLOCK-----

xsDNBGn5sK8BDACuzSrrTjpVf4ay06OYB6yY0J1PqKffihoNMtrQRZjAHxoAPC7L
TBVHV/XOZw5HJc+9R71z1JV+iYg6z3jPziGKzX8Fj3ZXlzJPmpf1PuETH3KdbvtJ
T4ny+OGntnJntUoRKRPhTirr6yNeBk/637O3CQXjtqFUPZnko8OI/o1yawIBhJJA
WicutjkkUgd28Bh6HV9EIumHtCBgn5/1A/fpm9624MMgYLsA8qjC4XsoovQvFCaO
8HEhvfzrrTZHjn/nPeB9SigxIxXW8YaTVqMdqul07o72m3eA2mf+LMu9a04FX/d4
wbxBLtELm+1jIrbtyaFZEMOLv/haSiS/Lj3btJH/EoucejoZ5SH49ksmVAmKOLkt
OaTQ8b2gEvP7iaKiIiszCCtOSRohr+2GvDsDeLvVZnlR3I+SPhHar7TPKjFz0G3D
PNolyjXywNqOAMpomSPi8lSwjAFsxOtQbcck/qRGRSNk4DAmH70pA+89MXfQXZ3q
t1Q01B1+sU0I8xsAEQEAAc0kVGVkZHkgQXN0aWUgPHRlZGR5LmFzdGllQHZhdGVz
LnRlY2g+wsENBBMBCAA3FiEEGAIew9LzHY3pdrqtZg+p0QLLz9AFAmn5sK8FCQWj
moACGwMECwkIBwUVCAkKCwUWAgMBAAAKCRBmD6nRAsvP0ID6DACGOktArFbLKHNz
uyOVCskwfUZPla6Zpd3GZ8r61SrAKePIr2BnpgPkd0hV3bSRkRLIrgjzR2NRCzfp
0x0HfuhcYfAYPR46XHTvjaJEv99sT/vGUG1BZguYDOScSEpgSNaNlYum3RKZbMuR
OxdK8G+YHccJY8PvWSq2K2yiae2KGiAv1yjnZxug9/PtDfX8vQFUSg2w1ukRDf50
wvDohN1zUQfFtofOP2xCRsDZiHAlQ0pF+aUjXQhPeP3IdpfWc8cyRLXF06Rk46YM
YCytweGtGdHcqAfrVthl84129ZPN422k/voW0sm14gjYlGcTUwgnYlFRk2FLq0Qe
KEDcS0aj3o3EVAQCrayoGzi1pnlIKE3PRGUcUzjGVvzQ/po24gOjwba9Egr/Wmu3
MQlx/7A8zT5QBzF/n+RYdLNQ0Eu6YnUwf0Z1uieqNaon+olyIRFiLb/hCZHO6ekN
f5vrm2clHUbQAYaPQebknujoKBo6ZLHg0WM1gZS01Gz+aUpKsUfOwM0EafmwsAEM
AKiQiZa3yQMmc/h3sDbfVHPSiBA4IMI/NAB7IotzPHq1GzCpsoVILAhF/INbWjxJ
3DbVf+en3/FvdVZg2S38xtnth0njNdlVKpyxm054phKjbdoFDwaknWolS4hrddTm
etSG5/52AjtmPFtlXAk0NmLvfJnW3seXVQbgM7sW/MNXPP5UKDpkGnLhnvej+GU0
s3109sJeXT5ImVdphFs9cvyZyBT9t1PbRowv58EgV0zE4hbAeVkULAbxFV5b/ExT
jjGVHoX7CVhWxvCiTqCUoXZRkUE9C3FnkzEFRkKbYu6NCfiHfEyB3Xyg9hfdrRgj
MRq907zCof+nDtWxGz1MSEuvTj1g9GZ049Bennqzjc/Q+0ovXoK4jm+Py0FiUGUa
A6yhexficjH+kCR/xDbVnWrMhSLB4AuTBT9HjfZI6gk3uYLhoT8Pig4/eVtR2Q1w
ZIJsFToR6ofGuyECwFcs+PUXN7fmGRSiPXgjAr/zIUBdW0VWCE3OGPNqtRk2E5s6
IQARAQABwsD8BBgBCAAmFiEEGAIew9LzHY3pdrqtZg+p0QLLz9AFAmn5sLAFCQWj
moACGwwACgkQZg+p0QLLz9DncQwAg76IehTemLIfrB8T9WIBZrI4kUV7G7a4rjiV
oUiHYN5QwhnbZnsaJDlt+Ezoqy/510eo2bCSzvW5xXYPgyjcuOPwgQo1Qp764Qxy
X6rld2f2RcWkDuBHun55ZWXjby8o21ginPRwruBVYY5rVf3DV1iBu4NurUeHtyFk
/dS0XTOQi2wVUb17sW/+ybCEokdVacZGzOqP/OmwHrF8ylXlXnhQq6e3r+J+T8fu
oGJelm/CJiMwyP6cEWE8sxVqX/iqwjwUYkuOCpE+lOWSvdNHgoEkWR0RXBPQjnGm
LKbfTl/QDXLk6NP2/r9uxm2HL6Ei3QJKSEdrp+XZaVnk/OffO485NOTKwGOxyWb0
06cTMh53xPkAJFQu4Tvdj+odsHz88jqw5wfPG0BYWx0I/FspYj7N9kZR8ULR9nX0
LvpzJ/kB4NgHIUt8YtIL6ZSfM2dbF7fKzvx1UqFfvozJZwFzfEieJLXa4nlGgR6D
x9fhaZEsniw8/bYgC3igkk5YJiOa
=lUIA
-----END PGP PUBLIC KEY BLOCK-----

OpenPGP_signature.asc (application/pgp-signature, 665 B)

-----BEGIN PGP SIGNATURE-----
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=U8KH
-----END PGP SIGNATURE-----