x86/kasan: Add helpers to align shadow addresses up and down

Add helpers to dedup code for aligning shadow address up/down to page
boundaries when translating an address to its shadow.

No functional change intended.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Link: https://lkml.kernel.org/r/20221110203504.1985010-5-seanjc@google.com

Author: sean-jc

arch/x86/mm/kasan_init_64.c

@@ -316,22 +316,33 @@ void __init kasan_early_init(void)
 	kasan_map_early_shadow(init_top_pgt);
 }
 
+static unsigned long kasan_mem_to_shadow_align_down(unsigned long va)
+{
+	unsigned long shadow = (unsigned long)kasan_mem_to_shadow((void *)va);
+
+	return round_down(shadow, PAGE_SIZE);
+}
+
+static unsigned long kasan_mem_to_shadow_align_up(unsigned long va)
+{
+	unsigned long shadow = (unsigned long)kasan_mem_to_shadow((void *)va);
+
+	return round_up(shadow, PAGE_SIZE);
+}
+
 void __init kasan_populate_shadow_for_vaddr(void *va, size_t size, int nid)
 {
 	unsigned long shadow_start, shadow_end;
 
-	shadow_start = (unsigned long)kasan_mem_to_shadow(va);
-	shadow_start = round_down(shadow_start, PAGE_SIZE);
-	shadow_end = (unsigned long)kasan_mem_to_shadow(va + size);
-	shadow_end = round_up(shadow_end, PAGE_SIZE);
-
+	shadow_start = kasan_mem_to_shadow_align_down((unsigned long)va);
+	shadow_end = kasan_mem_to_shadow_align_up((unsigned long)va + size);
 	kasan_populate_shadow(shadow_start, shadow_end, nid);
 }
 
 void __init kasan_init(void)
 {
+	unsigned long shadow_cea_begin, shadow_cea_end;
 	int i;
-	void *shadow_cea_begin, *shadow_cea_end;
 
 	memcpy(early_top_pgt, init_top_pgt, sizeof(early_top_pgt));
 
@@ -372,16 +383,9 @@ void __init kasan_init(void)
 		map_range(&pfn_mapped[i]);
 	}
 
-	shadow_cea_begin = (void *)CPU_ENTRY_AREA_BASE;
-	shadow_cea_begin = kasan_mem_to_shadow(shadow_cea_begin);
-	shadow_cea_begin = (void *)round_down(
-			(unsigned long)shadow_cea_begin, PAGE_SIZE);
-
-	shadow_cea_end = (void *)(CPU_ENTRY_AREA_BASE +
-					CPU_ENTRY_AREA_MAP_SIZE);
-	shadow_cea_end = kasan_mem_to_shadow(shadow_cea_end);
-	shadow_cea_end = (void *)round_up(
-			(unsigned long)shadow_cea_end, PAGE_SIZE);
+	shadow_cea_begin = kasan_mem_to_shadow_align_down(CPU_ENTRY_AREA_BASE);
+	shadow_cea_end = kasan_mem_to_shadow_align_up(CPU_ENTRY_AREA_BASE +
+						      CPU_ENTRY_AREA_MAP_SIZE);
 
 	kasan_populate_early_shadow(
 		kasan_mem_to_shadow((void *)PAGE_OFFSET + MAXMEM),
@@ -403,9 +407,9 @@ void __init kasan_init(void)
 
 	kasan_populate_early_shadow(
 		kasan_mem_to_shadow((void *)VMALLOC_END + 1),
-		shadow_cea_begin);
+		(void *)shadow_cea_begin);
 
-	kasan_populate_early_shadow(shadow_cea_end,
+	kasan_populate_early_shadow((void *)shadow_cea_end,
 			kasan_mem_to_shadow((void *)__START_KERNEL_map));
 
 	kasan_populate_shadow((unsigned long)kasan_mem_to_shadow(_stext),