exec: flush the whole TLB if a watchpoint crosses a page boundary

There is no particular reason why you can't have a watchpoint in TCG
that covers a large chunk of the address space. We could be clever
about it but these cases are pretty rare and we can assume the user
will expect a little performance degradation.

NB: In my testing gdb will silently squash a watchpoint like:

  watch (char[0x7fffffffff]) *0x0

to a 4 byte watchpoint. Practically it will limit the maximum size
based on max-value-size. However given enough of a tweak the sky is
the limit.

Reported-by: Alexander Bulekov <alxndr@bu.edu>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20200605154929.26910-5-alex.bennee@linaro.org>

1 files changed, 7 insertions, 1 deletions

diff --git a/exec.c b/exec.c
index be4be2df3a..a0bf9d61c8 100644
--- a/exec.c
+++ b/exec.c
@@ -1038,6 +1038,7 @@ int cpu_watchpoint_insert(CPUState *cpu, vaddr addr, vaddr len,
                           int flags, CPUWatchpoint **watchpoint)
 {
     CPUWatchpoint *wp;
+    vaddr in_page;
 
     /* forbid ranges which are empty or run off the end of the address space */
     if (len == 0 || (addr + len - 1) < addr) {
@@ -1058,7 +1059,12 @@ int cpu_watchpoint_insert(CPUState *cpu, vaddr addr, vaddr len,
         QTAILQ_INSERT_TAIL(&cpu->watchpoints, wp, entry);
     }
 
-    tlb_flush_page(cpu, addr);
+    in_page = -(addr | TARGET_PAGE_MASK);
+    if (len <= in_page) {
+        tlb_flush_page(cpu, addr);
+    } else {
+        tlb_flush(cpu);
+    }
 
     if (watchpoint)
         *watchpoint = wp;