Support software breakpoints in the debug server on Intel CPUs.

- Allow the userland hypervisor to intercept breakpoint exceptions
  (BP#) in the guest.  A new capability (VM_CAP_BPT_EXIT) is used to
  enable this feature.  These exceptions are reported to userland via
  a new VM_EXITCODE_BPT that includes the length of the original
  breakpoint instruction.  If userland wishes to pass the exception
  through to the guest, it must be explicitly re-injected via
  vm_inject_exception().

- Export VMCS_ENTRY_INST_LENGTH as a VM_REG_GUEST_ENTRY_INST_LENGTH
  pseudo-register.  Injecting a BP# on Intel requires setting this to
  the length of the breakpoint instruction.  AMD SVM currently ignores
  writes to this register (but reports success) and fails to read it.

- Rework the per-vCPU state tracked by the debug server.  Rather than
  a single 'stepping_vcpu' global, add a structure for each vCPU that
  tracks state about that vCPU ('stepping', 'stepped', and
  'hit_swbreak').  A global 'stopped_vcpu' tracks which vCPU is
  currently reporting an event.  Event handlers for MTRAP and
  breakpoint exits loop until the associated event is reported to the
  debugger.

  Breakpoint events are discarded if the breakpoint is not present
  when a vCPU resumes in the breakpoint handler to retry submitting
  the breakpoint event.

- Maintain a linked-list of active breakpoints in response to the GDB
  'Z0' and 'z0' packets.

Reviewed by:	markj (earlier version)
MFC after:	2 months
Differential Revision:	https://reviews.freebsd.org/D20309

1 files changed, 6 insertions, 0 deletions

diff --git a/sys/amd64/include/vmm.h b/sys/amd64/include/vmm.h
index 798d70b4d5c0..5b291dda265e 100644
--- a/sys/amd64/include/vmm.h
+++ b/sys/amd64/include/vmm.h
@@ -95,6 +95,7 @@ enum vm_reg_name {
 	VM_REG_GUEST_DR2,
 	VM_REG_GUEST_DR3,
 	VM_REG_GUEST_DR6,
+	VM_REG_GUEST_ENTRY_INST_LENGTH,
 	VM_REG_LAST
 };
 
@@ -455,6 +456,7 @@ enum vm_cap_type {
 	VM_CAP_PAUSE_EXIT,
 	VM_CAP_UNRESTRICTED_GUEST,
 	VM_CAP_ENABLE_INVPCID,
+	VM_CAP_BPT_EXIT,
 	VM_CAP_MAX
 };
 
@@ -580,6 +582,7 @@ enum vm_exitcode {
 	VM_EXITCODE_REQIDLE,
 	VM_EXITCODE_DEBUG,
 	VM_EXITCODE_VMINSN,
+	VM_EXITCODE_BPT,
 	VM_EXITCODE_MAX
 };
 
@@ -667,6 +670,9 @@ struct vm_exit {
 			uint64_t	exitinfo2;
 		} svm;
 		struct {
+			int		inst_length;
+		} bpt;
+		struct {
 			uint32_t	code;		/* ecx value */
 			uint64_t	wval;
 		} msr;