exec/memtxattr: add process identifier to the transaction attributes

Extend memory transaction attributes with process identifier to allow
per-request address translation logic to use requester_id / process_id
to identify memory mapping (e.g. enabling IOMMU w/ PASID translations).

Signed-off-by: Tomasz Jeznach <tjeznach@rivosinc.com>
Reviewed-by: Frank Chang <frank.chang@sifive.com>
Reviewed-by: Jason Chien <jason.chien@sifive.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Message-ID: <20241016204038.649340-2-dbarboza@ventanamicro.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

include/exec/memattrs.h

@@ -52,6 +52,11 @@ typedef struct MemTxAttrs {
     unsigned int memory:1;
     /* Requester ID (for MSI for example) */
     unsigned int requester_id:16;
+
+    /*
+     * PID (PCI PASID) support: Limited to 8 bits process identifier.
+     */
+    unsigned int pid:8;
 } MemTxAttrs;
 
 /* Bus masters which don't specify any attributes will get this,