mm: Add PG_arch_3 page flag

As with PG_arch_2, this flag is only allowed on 64-bit architectures due
to the shortage of bits available. It will be used by the arm64 MTE code
in subsequent patches.
Signed-off-by: Peter Collingbourne <pcc@google.com>
Cc: Will Deacon <will@kernel.org>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Steven Price <steven.price@arm.com>
[catalin.marinas@arm.com: added flag preserving in __split_huge_page_tail()]
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Reviewed-by: Steven Price <steven.price@arm.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20221104011041.290951-5-pcc@google.com

fs/proc/page.c

@@ -221,6 +221,7 @@ u64 stable_page_flags(struct page *page)
 	u |= kpf_copy_bit(k, KPF_ARCH,		PG_arch_1);
 #ifdef CONFIG_ARCH_USES_PG_ARCH_X
 	u |= kpf_copy_bit(k, KPF_ARCH_2,	PG_arch_2);
+	u |= kpf_copy_bit(k, KPF_ARCH_3,	PG_arch_3);
 #endif
 
 	return u;

include/linux/kernel-page-flags.h

@@ -18,5 +18,6 @@
 #define KPF_UNCACHED		39
 #define KPF_SOFTDIRTY		40
 #define KPF_ARCH_2		41
+#define KPF_ARCH_3		42
 
 #endif /* LINUX_KERNEL_PAGE_FLAGS_H */

include/linux/page-flags.h

@@ -134,6 +134,7 @@ enum pageflags {
 #endif
 #ifdef CONFIG_ARCH_USES_PG_ARCH_X
 	PG_arch_2,
+	PG_arch_3,
 #endif
 #ifdef CONFIG_KASAN_HW_TAGS
 	PG_skip_kasan_poison,

include/trace/events/mmflags.h

@@ -131,6 +131,7 @@ IF_HAVE_PG_HWPOISON(PG_hwpoison,	"hwpoison"	)		\
 IF_HAVE_PG_IDLE(PG_young,		"young"		)		\
 IF_HAVE_PG_IDLE(PG_idle,		"idle"		)		\
 IF_HAVE_PG_ARCH_X(PG_arch_2,		"arch_2"	)		\
+IF_HAVE_PG_ARCH_X(PG_arch_3,		"arch_3"	)		\
 IF_HAVE_PG_SKIP_KASAN_POISON(PG_skip_kasan_poison, "skip_kasan_poison")
 
 #define show_page_flags(flags)						\

mm/huge_memory.c

@@ -2446,6 +2446,7 @@ static void __split_huge_page_tail(struct page *head, int tail,
 			 (1L << PG_unevictable) |
 #ifdef CONFIG_ARCH_USES_PG_ARCH_X
 			 (1L << PG_arch_2) |
+			 (1L << PG_arch_3) |
 #endif
 			 (1L << PG_dirty) |
 			 LRU_GEN_MASK | LRU_REFS_MASK));