diff mbox series

[v5,06/25] mm: Add PG_ARCH_2 page flag

Message ID 20200624175244.25837-7-catalin.marinas@arm.com (mailing list archive)
State New, archived
Headers show
Series arm64: Memory Tagging Extension user-space support | expand

Commit Message

Catalin Marinas June 24, 2020, 5:52 p.m. UTC 
From: Steven Price <steven.price@arm.com>

For arm64 MTE support it is necessary to be able to mark pages that
contain user space visible tags that will need to be saved/restored e.g.
when swapped out.

To support this add a new arch specific flag (PG_ARCH_2) that arch code
can opt into using ARCH_USES_PG_ARCH_2.

Signed-off-by: Steven Price <steven.price@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
---

Notes:
    New in v4.

 fs/proc/page.c                    | 3 +++
 include/linux/kernel-page-flags.h | 1 +
 include/linux/page-flags.h        | 3 +++
 include/trace/events/mmflags.h    | 9 ++++++++-
 mm/Kconfig                        | 3 +++
 tools/vm/page-types.c             | 2 ++
 6 files changed, 20 insertions(+), 1 deletion(-)

Comments

Andrew Morton June 24, 2020, 6:33 p.m. UTC | #1 
On Wed, 24 Jun 2020 18:52:25 +0100 Catalin Marinas <catalin.marinas@arm.com> wrote:

> From: Steven Price <steven.price@arm.com>
> 
> For arm64 MTE support it is necessary to be able to mark pages that
> contain user space visible tags that will need to be saved/restored e.g.
> when swapped out.
> 
> To support this add a new arch specific flag (PG_ARCH_2) that arch code
> can opt into using ARCH_USES_PG_ARCH_2.
> 
> ...
>
> --- a/fs/proc/page.c
> +++ b/fs/proc/page.c
> @@ -217,6 +217,9 @@ 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_ARCH_USES_PG_ARCH_2
> +	u |= kpf_copy_bit(k, KPF_ARCH_2,	PG_arch_2);
> +#endif

Do we need CONFIG_ARCH_USES_PG_ARCH_2?  What would be the downside to
giving every architecture a PG_arch_2, but only arm64 uses it (at
present)?
Matthew Wilcox June 24, 2020, 6:36 p.m. UTC | #2 
On Wed, Jun 24, 2020 at 11:33:07AM -0700, Andrew Morton wrote:
> On Wed, 24 Jun 2020 18:52:25 +0100 Catalin Marinas <catalin.marinas@arm.com> wrote:
> 
> > From: Steven Price <steven.price@arm.com>
> > 
> > For arm64 MTE support it is necessary to be able to mark pages that
> > contain user space visible tags that will need to be saved/restored e.g.
> > when swapped out.
> > 
> > To support this add a new arch specific flag (PG_ARCH_2) that arch code
> > can opt into using ARCH_USES_PG_ARCH_2.
> > 
> > ...
> >
> > --- a/fs/proc/page.c
> > +++ b/fs/proc/page.c
> > @@ -217,6 +217,9 @@ 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_ARCH_USES_PG_ARCH_2
> > +	u |= kpf_copy_bit(k, KPF_ARCH_2,	PG_arch_2);
> > +#endif
> 
> Do we need CONFIG_ARCH_USES_PG_ARCH_2?  What would be the downside to
> giving every architecture a PG_arch_2, but only arm64 uses it (at
> present)?

32-bit architectures don't have space for it.  We could condition it on
CONFIG_64BIT instead.
Catalin Marinas June 25, 2020, 5:10 p.m. UTC | #3 
On Wed, Jun 24, 2020 at 07:36:47PM +0100, Matthew Wilcox wrote:
> On Wed, Jun 24, 2020 at 11:33:07AM -0700, Andrew Morton wrote:
> > On Wed, 24 Jun 2020 18:52:25 +0100 Catalin Marinas <catalin.marinas@arm.com> wrote:
> > > From: Steven Price <steven.price@arm.com>
> > > 
> > > For arm64 MTE support it is necessary to be able to mark pages that
> > > contain user space visible tags that will need to be saved/restored e.g.
> > > when swapped out.
> > > 
> > > To support this add a new arch specific flag (PG_ARCH_2) that arch code
> > > can opt into using ARCH_USES_PG_ARCH_2.
> > > 
> > > ...
> > >
> > > --- a/fs/proc/page.c
> > > +++ b/fs/proc/page.c
> > > @@ -217,6 +217,9 @@ 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_ARCH_USES_PG_ARCH_2
> > > +	u |= kpf_copy_bit(k, KPF_ARCH_2,	PG_arch_2);
> > > +#endif
> > 
> > Do we need CONFIG_ARCH_USES_PG_ARCH_2?  What would be the downside to
> > giving every architecture a PG_arch_2, but only arm64 uses it (at
> > present)?
> 
> 32-bit architectures don't have space for it.  We could condition it on
> CONFIG_64BIT instead.

I'll this, though we'd still need some #ifdefs (OTOH, we get rid of the
Kconfig entry).
Catalin Marinas July 1, 2020, 5:30 p.m. UTC | #4 
On Wed, Jun 24, 2020 at 11:33:07AM -0700, Andrew Morton wrote:
> On Wed, 24 Jun 2020 18:52:25 +0100 Catalin Marinas <catalin.marinas@arm.com> wrote:
> > From: Steven Price <steven.price@arm.com>
> > For arm64 MTE support it is necessary to be able to mark pages that
> > contain user space visible tags that will need to be saved/restored e.g.
> > when swapped out.
> > 
> > To support this add a new arch specific flag (PG_ARCH_2) that arch code
> > can opt into using ARCH_USES_PG_ARCH_2.
> > 
> > ...
> >
> > --- a/fs/proc/page.c
> > +++ b/fs/proc/page.c
> > @@ -217,6 +217,9 @@ 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_ARCH_USES_PG_ARCH_2
> > +	u |= kpf_copy_bit(k, KPF_ARCH_2,	PG_arch_2);
> > +#endif
> 
> Do we need CONFIG_ARCH_USES_PG_ARCH_2?  What would be the downside to
> giving every architecture a PG_arch_2, but only arm64 uses it (at
> present)?

It turns out we have another issue with this flag. PG_arch_2 in the
arm64 MTE patches is used to mark a page as having valid tags. During
set_pte_at(), if the mapping type is tagged, we set PG_arch_2 (also
setting it in other cases like copy_page). In combination with THP and
swap (and some stress-testing to force swap-out), the kernel ends up
clearing PG_arch_2 in __split_huge_page_tail(), causing a subsequent
set_pte_at() to zero valid tags stored by user.

The quick fix is to add an arch_huge_page_flags_split_preserve macro
(need to think of a shorter name) which adds 1L << PG_arch_2 to the
preserve list in the above mentioned function. However, I wonder whether
it's safe to add both PG_arch_1 and PG_arch_2 to this list. At least on
arm and arm64, PG_arch_1 is used to mark a page as D-cache clean (and
don't need to do this again after splitting a pmd):

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 78c84bee7e29..22b3236a6dd8 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2364,6 +2364,10 @@ static void __split_huge_page_tail(struct page *head, int tail,
 			 (1L << PG_workingset) |
 			 (1L << PG_locked) |
 			 (1L << PG_unevictable) |
+			 (1L << PG_arch_1) |
+#ifdef CONFIG_64BIT
+			 (1L << PG_arch_2) |
+#endif
 			 (1L << PG_dirty)));
 
 	/* ->mapping in first tail page is compound_mapcount */

Thanks.
diff mbox series

Patch

diff --git a/fs/proc/page.c b/fs/proc/page.c
index f909243d4a66..1b6cbe0849a8 100644
--- a/fs/proc/page.c
+++ b/fs/proc/page.c
@@ -217,6 +217,9 @@  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_ARCH_USES_PG_ARCH_2
+	u |= kpf_copy_bit(k, KPF_ARCH_2,	PG_arch_2);
+#endif
 
 	return u;
 };
diff --git a/include/linux/kernel-page-flags.h b/include/linux/kernel-page-flags.h
index abd20ef93c98..eee1877a354e 100644
--- a/include/linux/kernel-page-flags.h
+++ b/include/linux/kernel-page-flags.h
@@ -17,5 +17,6 @@ 
 #define KPF_ARCH		38
 #define KPF_UNCACHED		39
 #define KPF_SOFTDIRTY		40
+#define KPF_ARCH_2		41
 
 #endif /* LINUX_KERNEL_PAGE_FLAGS_H */
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 6be1aa559b1e..b40d7cb7c8e6 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -135,6 +135,9 @@  enum pageflags {
 #if defined(CONFIG_IDLE_PAGE_TRACKING) && defined(CONFIG_64BIT)
 	PG_young,
 	PG_idle,
+#endif
+#ifdef CONFIG_ARCH_USES_PG_ARCH_2
+	PG_arch_2,
 #endif
 	__NR_PAGEFLAGS,
 
diff --git a/include/trace/events/mmflags.h b/include/trace/events/mmflags.h
index 5fb752034386..5d098029a2d8 100644
--- a/include/trace/events/mmflags.h
+++ b/include/trace/events/mmflags.h
@@ -79,6 +79,12 @@ 
 #define IF_HAVE_PG_IDLE(flag,string)
 #endif
 
+#ifdef CONFIG_ARCH_USES_PG_ARCH_2
+#define IF_HAVE_PG_ARCH_2(flag,string) ,{1UL << flag, string}
+#else
+#define IF_HAVE_PG_ARCH_2(flag,string)
+#endif
+
 #define __def_pageflag_names						\
 	{1UL << PG_locked,		"locked"	},		\
 	{1UL << PG_waiters,		"waiters"	},		\
@@ -105,7 +111,8 @@  IF_HAVE_PG_MLOCK(PG_mlocked,		"mlocked"	)		\
 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_IDLE(PG_idle,		"idle"		)		\
+IF_HAVE_PG_ARCH_2(PG_arch_2,		"arch_2"	)
 
 #define show_page_flags(flags)						\
 	(flags) ? __print_flags(flags, "|",				\
diff --git a/mm/Kconfig b/mm/Kconfig
index f2104cc0d35c..21eddae15078 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -872,4 +872,7 @@  config ARCH_HAS_HUGEPD
 config MAPPING_DIRTY_HELPERS
         bool
 
+config ARCH_USES_PG_ARCH_2
+	bool
+
 endmenu
diff --git a/tools/vm/page-types.c b/tools/vm/page-types.c
index 58c0eab71bca..0517c744b04e 100644
--- a/tools/vm/page-types.c
+++ b/tools/vm/page-types.c
@@ -78,6 +78,7 @@ 
 #define KPF_ARCH		38
 #define KPF_UNCACHED		39
 #define KPF_SOFTDIRTY		40
+#define KPF_ARCH_2		41
 
 /* [48-] take some arbitrary free slots for expanding overloaded flags
  * not part of kernel API
@@ -135,6 +136,7 @@  static const char * const page_flag_names[] = {
 	[KPF_ARCH]		= "h:arch",
 	[KPF_UNCACHED]		= "c:uncached",
 	[KPF_SOFTDIRTY]		= "f:softdirty",
+	[KPF_ARCH_2]		= "H:arch_2",
 
 	[KPF_READAHEAD]		= "I:readahead",
 	[KPF_SLOB_FREE]		= "P:slob_free",