[v3,0/2] target/arm: kvm: Support for KVM DABT with no valid ISS

Message

Beata Michalska March 12, 2020, 12:33 a.m. UTC

Some of the ARMv7 & ARMv8 load/store instructions might trigger a data abort
exception with no valid ISS info to be decoded. The lack of decode info
makes it at least tricky to emulate the instruction which is one of the
(many) reasons why KVM will not even try to do so.

So far, if a guest made an attempt to access memory outside the memory slot,
KVM reported vague ENOSYS. As a result QEMU exited with no useful information
being provided or even a clue on what has just happened.

ARM KVM introduced support for notifying of an attempt to execute
an instruction that resulted in dabt with no valid ISS decoding info.
This still leaves QEMU to handle the case, but at least now it gives more
control and a start point for more meaningful handling of such cases.

This patchset relies on KVM to insert the external data abort into the guest.

v3:
 - Fix setting KVM cap per vm not per vcpu
 - Simplifying the handler to bare minimum with no default logging to address
   the potential risk of overflooding the host (adding support for rate
   limiting the logs turned out to be bit too invasive to justify the little
   add-on value from logs in this particular case)
 - Adding handling KVM bug (for small range of affected kernels):
   little bit of trade-off between what's reasonable and what's effective:
   aborting qemu when running on buggy host kernel

v2:
- Improving/re-phrasing messaging
- Dropping messing around with forced sync (@see [PATCH v2 1/2])
  and PC alignment


Beata Michalska (2):
  target/arm: kvm: Inject events at the last stage of sync
  target/arm: kvm: Handle DABT with no valid ISS

 target/arm/cpu.h     |  3 ++
 target/arm/kvm.c     | 81 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 target/arm/kvm32.c   | 41 ++++++++++++++++++++++----
 target/arm/kvm64.c   | 51 +++++++++++++++++++++++++++++----
 target/arm/kvm_arm.h | 22 ++++++++++++++
 5 files changed, 188 insertions(+), 10 deletions(-)