RISC-V ISA does not specify how to manage physical memory attributes (PMA).

So do nothing in pmap_page_set_memattr() and don't panic.

Reviewed by:	markj
Sponsored by:	DARPA, AFRL
Differential Revision:	https://reviews.freebsd.org/D20209

sys/riscv/riscv/pmap.c

@@ -4200,16 +4200,6 @@ pmap_page_set_memattr(vm_page_t m, vm_memattr_t ma)
 {
 
 	m->md.pv_memattr = ma;
-
-	/*
-	 * RISCVTODO: Implement the below (from the amd64 pmap)
-	 * If "m" is a normal page, update its direct mapping.  This update
-	 * can be relied upon to perform any cache operations that are
-	 * required for data coherence.
-	 */
-	if ((m->flags & PG_FICTITIOUS) == 0 &&
-	    PHYS_IN_DMAP(VM_PAGE_TO_PHYS(m)))
-		panic("RISCVTODO: pmap_page_set_memattr");
 }
 
 /*