tcg: Support MMU protection regions smaller than TARGET_PAGE_SIZE

Add support for MMU protection regions that are smaller than
TARGET_PAGE_SIZE. We do this by marking the TLB entry for those
pages with a flag TLB_RECHECK. This flag causes us to always
take the slow-path for accesses. In the slow path we can then
special case them to always call tlb_fill() again, so we have
the correct information for the exact address being accessed.

This change allows us to handle reading and writing from small
regions; we cannot deal with execution from the small region.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20180620130619.11362-2-peter.maydell@linaro.org

1 files changed, 4 insertions, 1 deletions

diff --git a/include/exec/cpu-all.h b/include/exec/cpu-all.h
index 7fa726b..7338f57 100644
--- a/include/exec/cpu-all.h
+++ b/include/exec/cpu-all.h
@@ -330,11 +330,14 @@ CPUArchState *cpu_copy(CPUArchState *env);
 #define TLB_NOTDIRTY        (1 << (TARGET_PAGE_BITS - 2))
 /* Set if TLB entry is an IO callback.  */
 #define TLB_MMIO            (1 << (TARGET_PAGE_BITS - 3))
+/* Set if TLB entry must have MMU lookup repeated for every access */
+#define TLB_RECHECK         (1 << (TARGET_PAGE_BITS - 4))
 
 /* Use this mask to check interception with an alignment mask
  * in a TCG backend.
  */
-#define TLB_FLAGS_MASK  (TLB_INVALID_MASK | TLB_NOTDIRTY | TLB_MMIO)
+#define TLB_FLAGS_MASK  (TLB_INVALID_MASK | TLB_NOTDIRTY | TLB_MMIO \
+                         | TLB_RECHECK)
 
 void dump_exec_info(FILE *f, fprintf_function cpu_fprintf);
 void dump_opcount_info(FILE *f, fprintf_function cpu_fprintf);