[PATCH v2 3/3] softmmu: fix watchpoints on memory used by vCPU internals

[Pavel Dovgalyuk <pavel.dovgalyuk@ispras.ru>]

When vCPU processes interrupt request or exception, it can save
register values to the memory. Watchpoints may also be set on
these memory cells. In this case watchpoint processing code should
not retranslate the block which accessed the memory, because there
is no such block at all. "After access" watchpoint also can't be
used in such case.
This patch adds some conditions to prevent failures when watchpoint
is set on memory used for saving the registers on interrupt request.

Signed-off-by: Pavel Dovgalyuk <Pavel.Dovgalyuk@ispras.ru>
---
 softmmu/physmem.c |   14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/softmmu/physmem.c b/softmmu/physmem.c
index 314f8b439c..53edcf9a51 100644
--- a/softmmu/physmem.c
+++ b/softmmu/physmem.c
@@ -886,6 +886,14 @@ void cpu_check_watchpoint(CPUState *cpu, vaddr addr, vaddr len,
 
     assert(tcg_enabled());
     if (cpu->watchpoint_hit) {
+        if (!ra) {
+            /*
+             * Another memory access after hitting the watchpoint.
+             * There is no translation block and interrupt request
+             * is already set.
+             */
+            return;
+        }
         /*
          * We re-entered the check after replacing the TB.
          * Now raise the debug interrupt so that it will
@@ -936,6 +944,12 @@ void cpu_check_watchpoint(CPUState *cpu, vaddr addr, vaddr len,
                 continue;
             }
             cpu->watchpoint_hit = wp;
+            if (!ra) {
+                /* We're not in the TB, can't stop before the access. */
+                g_assert(!(wp->flags & BP_STOP_BEFORE_ACCESS));
+                cpu_interrupt(cpu, CPU_INTERRUPT_DEBUG);
+                return;
+            }
 
             mmap_lock();
             /* This call also restores vCPU state */