KVM: arm64: guest debug, add SW break point support

This adds support for SW breakpoints inserted by userspace.

We do this by trapping all guest software debug exceptions to the
hypervisor (MDCR_EL2.TDE). The exit handler sets an exit reason of
KVM_EXIT_DEBUG with the kvm_debug_exit_arch structure holding the
exception syndrome information.

It will be up to userspace to extract the PC (via GET_ONE_REG) and
determine if the debug event was for a breakpoint it inserted. If not
userspace will need to re-inject the correct exception restart the
hypervisor to deliver the debug exception to the guest.

Any other guest software debug exception (e.g. single step or HW
assisted breakpoints) will cause an error and the VM to be killed. This
is addressed by later patches which add support for the other debug
types.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Christoffer Dall <christoffer.dall@linaro.org>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
index 19adfd385882..0f498da354f2 100644
--- a/Documentation/virtual/kvm/api.txt
+++ b/Documentation/virtual/kvm/api.txt
@@ -2693,7 +2693,7 @@ when running. Common control bits are:
 The top 16 bits of the control field are architecture specific control
 flags which can include the following:
 
-  - KVM_GUESTDBG_USE_SW_BP:     using software breakpoints [x86]
+  - KVM_GUESTDBG_USE_SW_BP:     using software breakpoints [x86, arm64]
   - KVM_GUESTDBG_USE_HW_BP:     using hardware breakpoints [x86, s390]
   - KVM_GUESTDBG_INJECT_DB:     inject DB type exception [x86]
   - KVM_GUESTDBG_INJECT_BP:     inject BP type exception [x86]