s390/kasan: move memory needs estimation into a function

Also correct rounding downs in estimation calculations.
Reviewed-by: Alexander Egorenkov <egorenar@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>

arch/s390/boot/kaslr.c

@@ -7,6 +7,7 @@
 #include <asm/cpacf.h>
 #include <asm/timex.h>
 #include <asm/sclp.h>
+#include <asm/kasan.h>
 #include "compressed/decompressor.h"
 #include "boot.h"
 
@@ -179,34 +180,19 @@ unsigned long get_random_base(unsigned long safe_addr)
 	if (memory_end_set)
 		memory_limit = min(memory_limit, memory_end);
 
+	/*
+	 * Avoid putting kernel in the end of physical memory
+	 * which kasan will use for shadow memory and early pgtable
+	 * mapping allocations.
+	 */
+	memory_limit -= kasan_estimate_memory_needs(memory_limit);
+
 	if (IS_ENABLED(CONFIG_BLK_DEV_INITRD) && INITRD_START && INITRD_SIZE) {
 		if (safe_addr < INITRD_START + INITRD_SIZE)
 			safe_addr = INITRD_START + INITRD_SIZE;
 	}
 	safe_addr = ALIGN(safe_addr, THREAD_SIZE);
 
-	if ((IS_ENABLED(CONFIG_KASAN))) {
-		/*
-		 * Estimate kasan memory requirements, which it will reserve
-		 * at the very end of available physical memory. To estimate
-		 * that, we take into account that kasan would require
-		 * 1/8 of available physical memory (for shadow memory) +
-		 * creating page tables for the whole memory + shadow memory
-		 * region (1 + 1/8). To keep page tables estimates simple take
-		 * the double of combined ptes size.
-		 */
-		memory_limit = get_mem_detect_end();
-		if (memory_end_set && memory_limit > memory_end)
-			memory_limit = memory_end;
-
-		/* for shadow memory */
-		kasan_needs = memory_limit / 8;
-		/* for paging structures */
-		kasan_needs += (memory_limit + kasan_needs) / PAGE_SIZE /
-			       _PAGE_ENTRIES * _PAGE_TABLE_SIZE * 2;
-		memory_limit -= kasan_needs;
-	}
-
 	kernel_size = vmlinux.image_size + vmlinux.bss_size;
 	if (safe_addr + kernel_size > memory_limit)
 		return 0;

arch/s390/include/asm/kasan.h

@@ -17,10 +17,36 @@ extern void kasan_early_init(void);
 extern void kasan_copy_shadow_mapping(void);
 extern void kasan_free_early_identity(void);
 extern unsigned long kasan_vmax;
+
+/*
+ * Estimate kasan memory requirements, which it will reserve
+ * at the very end of available physical memory. To estimate
+ * that, we take into account that kasan would require
+ * 1/8 of available physical memory (for shadow memory) +
+ * creating page tables for the whole memory + shadow memory
+ * region (1 + 1/8). To keep page tables estimates simple take
+ * the double of combined ptes size.
+ *
+ * physmem parameter has to be already adjusted if not entire physical memory
+ * would be used (e.g. due to effect of "mem=" option).
+ */
+static inline unsigned long kasan_estimate_memory_needs(unsigned long physmem)
+{
+	unsigned long kasan_needs;
+	unsigned long pages;
+	/* for shadow memory */
+	kasan_needs = round_up(physmem / 8, PAGE_SIZE);
+	/* for paging structures */
+	pages = DIV_ROUND_UP(physmem + kasan_needs, PAGE_SIZE);
+	kasan_needs += DIV_ROUND_UP(pages, _PAGE_ENTRIES) * _PAGE_TABLE_SIZE * 2;
+
+	return kasan_needs;
+}
 #else
 static inline void kasan_early_init(void) { }
 static inline void kasan_copy_shadow_mapping(void) { }
 static inline void kasan_free_early_identity(void) { }
+static inline unsigned long kasan_estimate_memory_needs(unsigned long physmem) { return 0; }
 #endif
 
 #endif