[PATCH v4 1/8] mm: Do not enable PG_arch_2 for all 64-bit architectures

[Steven Price]

On 21/09/2022 04:51, Peter Collingbourne wrote:
> From: Catalin Marinas <catalin.marinas at arm.com>
> 
> Commit 4beba9486abd ("mm: Add PG_arch_2 page flag") introduced a new
> page flag for all 64-bit architectures. However, even if an architecture
> is 64-bit, it may still have limited spare bits in the 'flags' member of
> 'struct page'. This may happen if an architecture enables SPARSEMEM
> without SPARSEMEM_VMEMMAP as is the case with the newly added loongarch.
> This architecture port needs 19 more bits for the sparsemem section
> information and, while it is currently fine with PG_arch_2, adding any
> more PG_arch_* flags will trigger build-time warnings.
> 
> Add a new CONFIG_ARCH_USES_PG_ARCH_X option which can be selected by
> architectures that need more PG_arch_* flags beyond PG_arch_1. Select it
> on arm64.
> 
> Signed-off-by: Catalin Marinas <catalin.marinas at arm.com>
> Signed-off-by: Peter Collingbourne <pcc at google.com>
> Reported-by: kernel test robot <lkp at intel.com>
> Cc: Andrew Morton <akpm at linux-foundation.org>
> Cc: Steven Price <steven.price at arm.com>

Reviewed-by: Steven Price <steven.price at arm.com>

> ---
>  arch/arm64/Kconfig             | 1 +
>  fs/proc/page.c                 | 2 +-
>  include/linux/page-flags.h     | 2 +-
>  include/trace/events/mmflags.h | 8 ++++----
>  mm/Kconfig                     | 8 ++++++++
>  mm/huge_memory.c               | 2 +-
>  6 files changed, 16 insertions(+), 7 deletions(-)
> 
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index f6737d2f37b2..f2435b62e0ba 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -1948,6 +1948,7 @@ config ARM64_MTE
>  	depends on ARM64_PAN
>  	select ARCH_HAS_SUBPAGE_FAULTS
>  	select ARCH_USES_HIGH_VMA_FLAGS
> +	select ARCH_USES_PG_ARCH_X
>  	help
>  	  Memory Tagging (part of the ARMv8.5 Extensions) provides
>  	  architectural support for run-time, always-on detection of
> diff --git a/fs/proc/page.c b/fs/proc/page.c
> index a2873a617ae8..6f4b4bcb9b0d 100644
> --- a/fs/proc/page.c
> +++ b/fs/proc/page.c
> @@ -218,7 +218,7 @@ u64 stable_page_flags(struct page *page)
>  	u |= kpf_copy_bit(k, KPF_PRIVATE_2,	PG_private_2);
>  	u |= kpf_copy_bit(k, KPF_OWNER_PRIVATE,	PG_owner_priv_1);
>  	u |= kpf_copy_bit(k, KPF_ARCH,		PG_arch_1);
> -#ifdef CONFIG_64BIT
> +#ifdef CONFIG_ARCH_USES_PG_ARCH_X
>  	u |= kpf_copy_bit(k, KPF_ARCH_2,	PG_arch_2);
>  #endif
>  
> diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
> index 0b0ae5084e60..5dc7977edf9d 100644
> --- a/include/linux/page-flags.h
> +++ b/include/linux/page-flags.h
> @@ -132,7 +132,7 @@ enum pageflags {
>  	PG_young,
>  	PG_idle,
>  #endif
> -#ifdef CONFIG_64BIT
> +#ifdef CONFIG_ARCH_USES_PG_ARCH_X
>  	PG_arch_2,
>  #endif
>  #ifdef CONFIG_KASAN_HW_TAGS
> diff --git a/include/trace/events/mmflags.h b/include/trace/events/mmflags.h
> index 11524cda4a95..4673e58a7626 100644
> --- a/include/trace/events/mmflags.h
> +++ b/include/trace/events/mmflags.h
> @@ -90,10 +90,10 @@
>  #define IF_HAVE_PG_IDLE(flag,string)
>  #endif
>  
> -#ifdef CONFIG_64BIT
> -#define IF_HAVE_PG_ARCH_2(flag,string) ,{1UL << flag, string}
> +#ifdef CONFIG_ARCH_USES_PG_ARCH_X
> +#define IF_HAVE_PG_ARCH_X(flag,string) ,{1UL << flag, string}
>  #else
> -#define IF_HAVE_PG_ARCH_2(flag,string)
> +#define IF_HAVE_PG_ARCH_X(flag,string)
>  #endif
>  
>  #ifdef CONFIG_KASAN_HW_TAGS
> @@ -129,7 +129,7 @@ IF_HAVE_PG_UNCACHED(PG_uncached,	"uncached"	)		\
>  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_2(PG_arch_2,		"arch_2"	)		\
> +IF_HAVE_PG_ARCH_X(PG_arch_2,		"arch_2"	)		\
>  IF_HAVE_PG_SKIP_KASAN_POISON(PG_skip_kasan_poison, "skip_kasan_poison")
>  
>  #define show_page_flags(flags)						\
> diff --git a/mm/Kconfig b/mm/Kconfig
> index ceec438c0741..a976cbb07bd6 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -999,6 +999,14 @@ config ARCH_USES_HIGH_VMA_FLAGS
>  config ARCH_HAS_PKEYS
>  	bool
>  
> +config ARCH_USES_PG_ARCH_X
> +	bool
> +	help
> +	  Enable the definition of PG_arch_x page flags with x > 1. Only
> +	  suitable for 64-bit architectures with CONFIG_FLATMEM or
> +	  CONFIG_SPARSEMEM_VMEMMAP enabled, otherwise there may not be
> +	  enough room for additional bits in page->flags.
> +
>  config VM_EVENT_COUNTERS
>  	default y
>  	bool "Enable VM event counters for /proc/vmstat" if EXPERT
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 1cc4a5f4791e..24974a4ce28f 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -2444,7 +2444,7 @@ static void __split_huge_page_tail(struct page *head, int tail,
>  			 (1L << PG_workingset) |
>  			 (1L << PG_locked) |
>  			 (1L << PG_unevictable) |
> -#ifdef CONFIG_64BIT
> +#ifdef CONFIG_ARCH_USES_PG_ARCH_X
>  			 (1L << PG_arch_2) |
>  #endif
>  			 (1L << PG_dirty) |