exec: Add target-specific tlb bits to MemTxAttrs

These bits can be used to cache target-specific data in cputlb
read from the page tables.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 20190128223118.5255-5-richard.henderson@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

include/exec/memattrs.h

@@ -37,6 +37,16 @@ typedef struct MemTxAttrs {
     unsigned int user:1;
     /* Requester ID (for MSI for example) */
     unsigned int requester_id:16;
+    /*
+     * The following are target-specific page-table bits.  These are not
+     * related to actual memory transactions at all.  However, this structure
+     * is part of the tlb_fill interface, cached in the cputlb structure,
+     * and has unused bits.  These fields will be read by target-specific
+     * helpers using env->iotlb[mmu_idx][tlb_index()].attrs.target_tlb_bitN.
+     */
+    unsigned int target_tlb_bit0 : 1;
+    unsigned int target_tlb_bit1 : 1;
+    unsigned int target_tlb_bit2 : 1;
 } MemTxAttrs;
 
 /* Bus masters which don't specify any attributes will get this,