refine description of spmp check and exception priority

spmp_spec.adoc

@@ -2,11 +2,13 @@
 == S-mode Physical Memory Protection (SPMP)
 
 An optional RISC-V S-mode Physical Memory Protection (SPMP) provides per-hart supervisor-mode control registers to allow physical memory access privileges (read, write, execute) to be specified for each physical memory region.
-The SPMP is checked before the PMA and PMP checks, the same as paged virtual memory.
 The SPMP is also applied to data accesses in M-mode when the MPRV bit in mstatus is set and the MPP field in mstatus contains S or U.
 
 Like PMP, the granularity of SPMP access control settings is platform-specific and, within a platform, may vary by physical memory region. However, the standard SPMP encoding should support regions as small as four bytes. 
 
+SPMP checks can happen in parallel with PMA and PMP.
+The SPMP exception reports have higher priority than PMP or PMA exceptions (e.g., an SPMP exception will be raised if the access violates both SPMP and PMP).
+
 SPMP checks will be applied to all accesses for U mode and S mode, depending on the values in the configuration registers.
 M-mode accesses are not affected and always pass SPMP permission checks.
 SPMP registers can always be modified by M-mode and S-mode software.