[RFC] exec: flush CPU TB cache when breakpoint address translation fails

[Max Filippov <jcmvbkbc@gmail.com>]

When a breakpoint is inserted at location for which there's currently no
virtual to physical translation no action is taken on CPU TB cache. If a
TB for that virtual address already exists but is not visible ATM the
breakpoint won't be hit next time an instruction at that address will be
executed.

Flush entire CPU TB cache when a breakpoint is set for a virtual address
that cannot be translated to physical address.

This change fixes the following workflow:
- linux user application is running
- a breakpoint is inserted from QEMU gdbstub for a user address that is
  not currently present in the target CPU TLB
- an instruction at that address is executed, but the external debugger
  doesn't get control.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
---
 exec.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/exec.c b/exec.c
index ffdb5185353b..918945f8097e 100644
--- a/exec.c
+++ b/exec.c
@@ -1024,6 +1024,8 @@ static void breakpoint_invalidate(CPUState *cpu, target_ulong pc)
         /* Locks grabbed by tb_invalidate_phys_addr */
         tb_invalidate_phys_addr(cpu->cpu_ases[asidx].as,
                                 phys | (pc & ~TARGET_PAGE_MASK), attrs);
+    } else {
+        tb_flush(cpu);
     }
 }
 #endif
-- 
2.20.1