pmap: Degrade pmap_page_set_attr*() into a no-op on same attribute

For 32-bit arm, move the no-op test that was already in place at start
of the function so that it stays first even if the '#if 0' block around
the call to sf_buf_invalidate_cache() is uncommented at some point (if
ever).

Reviewed by:    jeffpc_josefsipek.net, kib
MFC after:      10 days
Sponsored by:   The FreeBSD Foundation
Differential Revision:  https://reviews.freebsd.org/D51253

sys/amd64/amd64/pmap.c

@@ -9649,6 +9649,8 @@ pmap_demote_pdpe(pmap_t pmap, pdp_entry_t *pdpe, vm_offset_t va, vm_page_t m)
 void
 pmap_page_set_memattr(vm_page_t m, vm_memattr_t ma)
 {
+	if (m->md.pat_mode == ma)
+		return;
 
 	m->md.pat_mode = ma;
 
@@ -9668,6 +9670,9 @@ pmap_page_set_memattr_noflush(vm_page_t m, vm_memattr_t ma)
 {
 	int error;
 
+	if (m->md.pat_mode == ma)
+		return;
+
 	m->md.pat_mode = ma;
 
 	if ((m->flags & PG_FICTITIOUS) != 0)

sys/arm/arm/pmap-v6.c

@@ -5767,7 +5767,7 @@ pmap_page_set_memattr(vm_page_t m, vm_memattr_t ma)
 
 	CTR5(KTR_PMAP, "%s: page %p - 0x%08X oma: %d, ma: %d", __func__, m,
 	    VM_PAGE_TO_PHYS(m), oma, ma);
-	if ((m->flags & PG_FICTITIOUS) != 0)
+	if (ma == oma || (m->flags & PG_FICTITIOUS) != 0)
 		return;
 #if 0
 	/*
@@ -5784,7 +5784,6 @@ pmap_page_set_memattr(vm_page_t m, vm_memattr_t ma)
 	 * If page is not mapped by sf buffer, map the page
 	 * transient and do invalidation.
 	 */
-	if (ma != oma) {
 	pa = VM_PAGE_TO_PHYS(m);
 	sched_pin();
 	pc = get_pcpu();
@@ -5800,7 +5799,6 @@ pmap_page_set_memattr(vm_page_t m, vm_memattr_t ma)
 	sched_unpin();
 	mtx_unlock(&pc->pc_cmap_lock);
 }
-}
 
 /*
  *  Miscellaneous support routines follow

sys/arm64/arm64/pmap.c

@@ -8045,6 +8045,8 @@ pmap_unmapbios(void *p, vm_size_t size)
 void
 pmap_page_set_memattr(vm_page_t m, vm_memattr_t ma)
 {
+	if (m->md.pv_memattr == ma)
+		return;
 
 	m->md.pv_memattr = ma;
 

sys/i386/i386/pmap.c

@@ -5617,6 +5617,8 @@ __CONCAT(PMTYPE, unmapdev)(void *p, vm_size_t size)
 static void
 __CONCAT(PMTYPE, page_set_memattr)(vm_page_t m, vm_memattr_t ma)
 {
+	if (m->md.pat_mode == ma)
+		return;
 
 	m->md.pat_mode = ma;
 	if ((m->flags & PG_FICTITIOUS) != 0)

sys/powerpc/aim/mmu_oea.c

@@ -1469,6 +1469,9 @@ moea_page_set_memattr(vm_page_t m, vm_memattr_t ma)
 	pmap_t	pmap;
 	u_int	lo;
 
+	if (m->md.mdpg_cache_attrs == ma)
+		return;
+
 	if ((m->oflags & VPO_UNMANAGED) != 0) {
 		m->md.mdpg_cache_attrs = ma;
 		return;

sys/powerpc/aim/mmu_oea64.c

@@ -2134,6 +2134,9 @@ moea64_page_set_memattr(vm_page_t m, vm_memattr_t ma)
 	CTR3(KTR_PMAP, "%s: pa=%#jx, ma=%#x",
 	    __func__, (uintmax_t)VM_PAGE_TO_PHYS(m), ma);
 
+	if (m->md.mdpg_cache_attrs == ma)
+		return;
+
 	if ((m->oflags & VPO_UNMANAGED) != 0) {
 		m->md.mdpg_cache_attrs = ma;
 		return;

sys/powerpc/aim/mmu_radix.c

@@ -5937,6 +5937,10 @@ mmu_radix_page_set_memattr(vm_page_t m, vm_memattr_t ma)
 {
 
 	CTR3(KTR_PMAP, "%s(%p, %#x)", __func__, m, ma);
+
+	if (m->md.mdpg_cache_attrs == ma)
+		return;
+
 	m->md.mdpg_cache_attrs = ma;
 
 	/*

sys/riscv/riscv/pmap.c

@@ -4838,6 +4838,8 @@ pmap_unmapbios(void *p, vm_size_t size)
 void
 pmap_page_set_memattr(vm_page_t m, vm_memattr_t ma)
 {
+	if (m->md.pv_memattr == ma)
+		return;
 
 	m->md.pv_memattr = ma;