powerpc/mm: Leave a gap between early allocated IO areas

Vmalloc system leaves a gap between allocated areas. It helps catching
overflows.

Do the same for IO areas which are allocated with early_ioremap_range()
until slab_is_available().
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/c433e358190fb5d47650463ea1ab755fc7b73e6e.1618828806.git.christophe.leroy@csgroup.eu

arch/powerpc/mm/ioremap_32.c

@@ -70,10 +70,10 @@ __ioremap_caller(phys_addr_t addr, unsigned long size, pgprot_t prot, void *call
 	 */
 	pr_warn("ioremap() called early from %pS. Use early_ioremap() instead\n", caller);
 
-	err = early_ioremap_range(ioremap_bot - size, p, size, prot);
+	err = early_ioremap_range(ioremap_bot - size - PAGE_SIZE, p, size, prot);
 	if (err)
 		return NULL;
-	ioremap_bot -= size;
+	ioremap_bot -= size + PAGE_SIZE;
 
 	return (void __iomem *)ioremap_bot + offset;
 }

arch/powerpc/mm/ioremap_64.c

@@ -38,7 +38,7 @@ void __iomem *__ioremap_caller(phys_addr_t addr, unsigned long size,
 		return NULL;
 
 	ret = (void __iomem *)ioremap_bot + offset;
-	ioremap_bot += size;
+	ioremap_bot += size + PAGE_SIZE;
 
 	return ret;
 }