Sorry for the delay in following up on this; as mentioned in the
description, since this is a limitation of the underlying vhost-user
specificiation, there are only 2 possible ways to address it: 1) change
qemu to use the newer vhost-user function which doesn't have the
8-region limit, and 2) fix/patch qemu as much as possible to
ignore/elide memory regions that the vhost-user implementation won't
need to access, to reduce the total number.
The #1 change to use the new api function is already done by upstream
qemu starting in v5.1.0, which is included in hirsute (see comment 1 for
upstream commit references).
The #2 change has been done upstream in various patches, and some of
those patches were backported in bug 1887525. There may be other
upstream patches for this that could further help, but that should be
investigated and handled in a separate new bug, IFF someone encounters
the 8-region limit again in the future; the usage of vhost-user is
rather narrow (just dpdk I believe) and generally the instances do not
have a huge number of discontinuous memory regions.
So for this bug, I believe the question is if the new vhost-user
function should be proactively backported to sru releases, and I think
the answer to that should be no. For the sru to be useful, the dpdk
package would also need to be updated to support the new vhost-user api
function, and the backporting of this has the potential to introduce
regressions.
So I believe we should reject this bug as wontfix, without a clear and
immediate need for this backporting work, as well as explanation of why
the dpdk instance(s) can't simply be adjusted to reduce their number of
discontiguous memory regions, and also after investigation into other
patches that might workaround the limit (as mentioned in #2).
Note that since the commits are included in hirsute, I'll mark this
fixreleased in h, and wontfix for sru releases.
** Also affects: qemu (Ubuntu Groovy)
Importance: Undecided
Status: New
** Also affects: qemu (Ubuntu Focal)
Importance: Undecided
Status: New
** Also affects: qemu (Ubuntu Bionic)
Importance: Undecided
Status: New
** Also affects: qemu (Ubuntu Hirsute)
Importance: Undecided
Status: New
** Changed in: qemu (Ubuntu Hirsute)
Status: New => Fix Released
** Changed in: qemu (Ubuntu Groovy)
Status: New => Won't Fix
** Changed in: qemu (Ubuntu Bionic)
Status: New => Won't Fix
** Changed in: qemu (Ubuntu Focal)
Status: New => Won't Fix
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https://bugs.launchpad.net/bugs/1886704
Title:
qemu fails to init vhost_user if > 8 memory regions
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