[v2,0/2] Improve handling of stage 2 aborts without instruction decode

Message

Christoffer Dall Oct. 8, 2019, 9:36 a.m. UTC

When a guest accesses memory outside the memory slots, KVM usually
bounces the access back to userspace with KVM_EXIT_MMIO.  However, on
arm/arm64 systems, certain load/store instructions did not provide
decoding info for the hypervisor to emulate the instruction, and in this
case KVM has rather rudely returned -ENOSYS and printed a not overly
helpful error message:

  load/store instruction decoding not implemented

This patch series improves the error message and allows userspace to be
notified of this event instead of receiving -ENOSYS, and also allows
userspace to ask KVM to inject an external abort to the guest, which it
can use for any memory access that it either cannot handle.

One remaining case which this patch set does not address is if the guest
accesses an in-kernel emulated device, such as the VGIC, but using a
load/store instruction which doesn't provide decode info.  With these
patches, this will return to userspace for it to handle, but there's no
way for userspace to return the decoding information to KVM and have KVM
complete the access to the in-kernel emulated device.  I have no plans
to address this limitation.

Changes since v1:
 - Rebased on v5.4-rc2
 - Fixed some documentation and coding nit in review of v1

Christoffer Dall (2):
  KVM: arm/arm64: Allow reporting non-ISV data aborts to userspace
  KVM: arm/arm64: Allow user injection of external data aborts

 Documentation/virt/kvm/api.txt       | 51 +++++++++++++++++++++++++++-
 arch/arm/include/asm/kvm_arm.h       |  1 +
 arch/arm/include/asm/kvm_emulate.h   |  5 +++
 arch/arm/include/asm/kvm_host.h      |  8 +++++
 arch/arm/include/uapi/asm/kvm.h      |  3 +-
 arch/arm/kvm/guest.c                 |  3 ++
 arch/arm64/include/asm/kvm_emulate.h |  5 +++
 arch/arm64/include/asm/kvm_host.h    |  8 +++++
 arch/arm64/include/uapi/asm/kvm.h    |  3 +-
 arch/arm64/kvm/guest.c               |  3 ++
 arch/arm64/kvm/inject_fault.c        |  4 +--
 include/uapi/linux/kvm.h             |  8 +++++
 virt/kvm/arm/arm.c                   | 22 ++++++++++++
 virt/kvm/arm/mmio.c                  |  9 ++++-
 14 files changed, 127 insertions(+), 6 deletions(-)