cputlb: Filter flushes on already clean tlbs

Especially for guests with large numbers of tlbs, like ARM or PPC,
we may well not use all of them in between flush operations.
Remember which tlbs have been used since the last flush, and
avoid any useless flushing.

Tested-by: Emilio G. Cota <cota@braap.org>
Reviewed-by: Emilio G. Cota <cota@braap.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

1 files changed, 6 insertions, 1 deletions

diff --git a/include/exec/cpu-defs.h b/include/exec/cpu-defs.h
index c7b501d..ca0fea8 100644
--- a/include/exec/cpu-defs.h
+++ b/include/exec/cpu-defs.h
@@ -166,7 +166,12 @@ typedef struct CPUTLBCommon {
      * mmu_idx may be discarded.  Protected by tlb_c.lock.
      */
     uint16_t pending_flush;
-
+    /*
+     * Within dirty, for each bit N, modifications have been made to
+     * mmu_idx N since the last time that mmu_idx was flushed.
+     * Protected by tlb_c.lock.
+     */
+    uint16_t dirty;
     /*
      * Statistics.  These are not lock protected, but are read and
      * written atomically.  This allows the monitor to print a snapshot