[Qemu-commits] [qemu/qemu] 6d2479: Revert series "spapr/xive: Allocate vCPU IPIs from...

[Peter Maydell]

  Branch: refs/heads/master
  Home:   https://github.com/qemu/qemu
  Commit: 6d24795ee7e3199d199d3c415312c93382ad1807
      
https://github.com/qemu/qemu/commit/6d24795ee7e3199d199d3c415312c93382ad1807
  Author: Greg Kurz <groug@kaod.org>
  Date:   2020-11-18 (Wed, 18 Nov 2020)

  Changed paths:
    M hw/intc/spapr_xive_kvm.c

  Log Message:
  -----------
  Revert series "spapr/xive: Allocate vCPU IPIs from the vCPU contexts"

This series was largely built on the assumption that IPI numbers are
numerically equal to vCPU ids. Even if this happens to be the case
in practice with the default machine settings, this ceases to be true
if VSMT is set to a different value than the number of vCPUs per core.
This causes bogus IPI numbers to be created in KVM from a guest stand
point. This leads to unknow results in the guest, including crashes
or missing vCPUs (see BugLink) and even non-fatal oopses in current
KVM that lacks a check before accessing misconfigured HW (see [1]).

A tentative patch was sent (see [2]) but it seems too complex to be
merged in an RC. Since the original changes are essentially an
optimization, it seems safer to revert them for now. The damage is
done by commit acbdb9956fe9 ("spapr/xive: Allocate IPIs independently
from the other sources") but the previous patches in the series are
really preparatory patches. So this reverts the whole series:

eab0a2d06e97 ("spapr/xive: Allocate vCPU IPIs from the vCPU contexts")
acbdb9956fe9 ("spapr/xive: Allocate IPIs independently from the other sources")
fa94447a2cd6 ("spapr/xive: Use kvmppc_xive_source_reset() in post_load")
235d3b116213 ("spapr/xive: Modify kvm_cpu_is_enabled() interface")

[1] https://marc.info/?l=kvm-ppc&m=160458409722959&w=4
[2] https://lists.gnu.org/archive/html/qemu-devel/2020-11/msg03626.html

Reported-by: Satheesh Rajendran <sathnaga@linux.vnet.ibm.com>
Fixes: acbdb9956fe9 ("spapr/xive: Allocate IPIs independently from the other 
sources")
BugLink: https://bugs.launchpad.net/qemu/+bug/1900241
Signed-off-by: Greg Kurz <groug@kaod.org>
Acked-by: Cédric Le Goater <clg@kaod.org>
Message-Id: <160554086275.1325084.12110142252189044646.stgit@bahia.lan>


  Commit: 3d275bd17c7bdf5acd4e4f58fa7b8b9114bb7484
      
https://github.com/qemu/qemu/commit/3d275bd17c7bdf5acd4e4f58fa7b8b9114bb7484
  Author: Peter Maydell <peter.maydell@linaro.org>
  Date:   2020-11-18 (Wed, 18 Nov 2020)

  Changed paths:
    M hw/intc/spapr_xive_kvm.c

  Log Message:
  -----------
  Merge remote-tracking branch 'remotes/gkurz/tags/ppc-for-5.2-20201118' into 
staging

ppc patch queue for 2020-11-18

This fixes a regression that badly breaks some guest setups because
IPIs end up misconfigured in the XIVE interrupt controller. Hopefully,
the last fix for sPAPR. I'm sending this PR with the blessing of David
who is currently on holidays.

# gpg: Signature made Wed 18 Nov 2020 10:26:31 GMT
# gpg:                using RSA key B4828BAF943140CEF2A3491071D4D5E5822F73D6
# gpg: Good signature from "Greg Kurz <groug@kaod.org>" [full]
# gpg:                 aka "Gregory Kurz <gregory.kurz@free.fr>" [full]
# gpg:                 aka "[jpeg image of size 3330]" [full]
# Primary key fingerprint: B482 8BAF 9431 40CE F2A3  4910 71D4 D5E5 822F 73D6

* remotes/gkurz/tags/ppc-for-5.2-20201118:
  Revert series "spapr/xive: Allocate vCPU IPIs from the vCPU contexts"

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>


Compare: https://github.com/qemu/qemu/compare/b696f2c6ba8c...3d275bd17c7b