[PATCH RFC v2 1/4] mm/ptshare: Add vm flag for shared PTE

From: Khalid Aziz <khalid.aziz@oracle.com>
To: akpm@linux-foundation.org, willy@infradead.org,
	markhemm@googlemail.com, viro@zeniv.linux.org.uk,
	david@redhat.com, mike.kravetz@oracle.com
Cc: Khalid Aziz <khalid.aziz@oracle.com>,
	andreyknvl@gmail.com, dave.hansen@intel.com, luto@kernel.org,
	brauner@kernel.org, arnd@arndb.de, ebiederm@xmission.com,
	catalin.marinas@arm.com, linux-arch@vger.kernel.org,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	mhiramat@kernel.org, rostedt@goodmis.org,
	vasily.averin@linux.dev, xhao@linux.alibaba.com, pcc@google.com,
	neilb@suse.de, maz@kernel.org
Subject: [PATCH RFC v2 1/4] mm/ptshare: Add vm flag for shared PTE
Date: Wed, 26 Apr 2023 10:49:48 -0600	[thread overview]
Message-ID: <a1bc313a3f50f085ab9fcd9826b3cdc20bc15269.1682453344.git.khalid.aziz@oracle.com> (raw)
In-Reply-To: <cover.1682453344.git.khalid.aziz@oracle.com>

Add a bit to vm_flags to indicate a vma shares PTEs with others. Add
a function to determine if a vma shares PTE by checking this flag.
This is to be used to find the shared page table entries on page fault
for vmas sharing PTE.

Signed-off-by: Khalid Aziz <khalid.aziz@oracle.com>
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
 include/linux/mm.h             | 8 ++++++++
 include/trace/events/mmflags.h | 3 ++-
 mm/internal.h                  | 5 +++++
 3 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 1f79667824eb..539becab551a 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -326,11 +326,13 @@ extern unsigned int kobjsize(const void *objp);
 #define VM_HIGH_ARCH_BIT_2	34	/* bit only usable on 64-bit architectures */
 #define VM_HIGH_ARCH_BIT_3	35	/* bit only usable on 64-bit architectures */
 #define VM_HIGH_ARCH_BIT_4	36	/* bit only usable on 64-bit architectures */
+#define VM_HIGH_ARCH_BIT_5	37	/* bit only usable on 64-bit architectures */
 #define VM_HIGH_ARCH_0	BIT(VM_HIGH_ARCH_BIT_0)
 #define VM_HIGH_ARCH_1	BIT(VM_HIGH_ARCH_BIT_1)
 #define VM_HIGH_ARCH_2	BIT(VM_HIGH_ARCH_BIT_2)
 #define VM_HIGH_ARCH_3	BIT(VM_HIGH_ARCH_BIT_3)
 #define VM_HIGH_ARCH_4	BIT(VM_HIGH_ARCH_BIT_4)
+#define VM_HIGH_ARCH_5	BIT(VM_HIGH_ARCH_BIT_5)
 #endif /* CONFIG_ARCH_USES_HIGH_VMA_FLAGS */
 
 #ifdef CONFIG_ARCH_HAS_PKEYS
@@ -372,6 +374,12 @@ extern unsigned int kobjsize(const void *objp);
 # define VM_MTE_ALLOWED	VM_NONE
 #endif
 
+#ifdef CONFIG_ARCH_USES_HIGH_VMA_FLAGS
+#define VM_SHARED_PT	VM_HIGH_ARCH_5
+#else
+#define VM_SHARED_PT	VM_NONE
+#endif
+
 #ifndef VM_GROWSUP
 # define VM_GROWSUP	VM_NONE
 #endif
diff --git a/include/trace/events/mmflags.h b/include/trace/events/mmflags.h
index 9db52bc4ce19..26f751e76c46 100644
--- a/include/trace/events/mmflags.h
+++ b/include/trace/events/mmflags.h
@@ -194,7 +194,8 @@ IF_HAVE_VM_SOFTDIRTY(VM_SOFTDIRTY,	"softdirty"	)		\
 	{VM_MIXEDMAP,			"mixedmap"	},		\
 	{VM_HUGEPAGE,			"hugepage"	},		\
 	{VM_NOHUGEPAGE,			"nohugepage"	},		\
-	{VM_MERGEABLE,			"mergeable"	}		\
+	{VM_MERGEABLE,			"mergeable"	},		\
+	{VM_SHARED_PT,			"sharedpt"	}		\
 
 #define show_vma_flags(flags)						\
 	(flags) ? __print_flags(flags, "|",				\
diff --git a/mm/internal.h b/mm/internal.h
index 7920a8b7982e..4d60d2d5fe19 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -1042,4 +1042,9 @@ struct vma_prepare {
 	struct vm_area_struct *remove;
 	struct vm_area_struct *remove2;
 };
+
+static inline bool vma_is_shared(const struct vm_area_struct *vma)
+{
+	return vma->vm_flags & VM_SHARED_PT;
+}
 #endif	/* __MM_INTERNAL_H */
-- 
2.37.2

