arm64: memory: fix flipped VA space fallout

VA_START used to be the start of the TTBR1 address space, but now it's a
point midway though. In a couple of places we still use VA_START to get
the start of the TTBR1 address space, so let's fix these up to use
PAGE_OFFSET instead.

Fixes: 14c127c9 ("arm64: mm: Flip kernel VA space")
Signed-off-by: NMark Rutland <mark.rutland@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Tested-by: NSteve Capper <steve.capper@arm.com>
Reviewed-by: NSteve Capper <steve.capper@arm.com>
Signed-off-by: NWill Deacon <will@kernel.org>

arch/arm64/mm/dump.c

@@ -400,7 +400,7 @@ void ptdump_check_wx(void)
 		.check_wx = true,
 	};
 
-	walk_pgd(&st, &init_mm, VA_START);
+	walk_pgd(&st, &init_mm, PAGE_OFFSET);
 	note_page(&st, 0, 0, 0);
 	if (st.wx_pages || st.uxn_pages)
 		pr_warn("Checked W+X mappings: FAILED, %lu W+X pages found, %lu non-UXN pages found\n",

arch/arm64/mm/fault.c

@@ -109,7 +109,7 @@ static inline bool is_ttbr0_addr(unsigned long addr)
 static inline bool is_ttbr1_addr(unsigned long addr)
 {
 	/* TTBR1 addresses may have a tag if KASAN_SW_TAGS is in use */
-	return arch_kasan_reset_tag(addr) >= VA_START;
+	return arch_kasan_reset_tag(addr) >= PAGE_OFFSET;
 }
 
 /*