linux-kernel - [RFC PATCH 1/2] mm/ptshare: Add vm flag for shared PTE

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Message-Id: <fb672fcc0aae77214a905e95808f9566f441218a.1670287696.git.khalid.aziz@oracle.com>
Date:   Tue,  6 Dec 2022 08:41:40 -0700
From:   Khalid Aziz <khalid@...ehiking.org>
To:     akpm@...ux-foundation.org, willy@...radead.org, djwong@...nel.org,
        markhemm@...glemail.com, viro@...iv.linux.org.uk, david@...hat.com,
        mike.kravetz@...cle.com
Cc:     Khalid Aziz <khalid@...ehiking.org>, andreyknvl@...il.com,
        dave.hansen@...el.com, luto@...nel.org, 21cnbao@...il.com,
        arnd@...db.de, ebiederm@...ssion.com, elver@...gle.com,
        linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, mhiramat@...nel.org, rostedt@...dmis.org,
        vasily.averin@...ux.dev, Khalid Aziz <khalid.aziz@...cle.com>
Subject: [RFC PATCH 1/2] mm/ptshare: Add vm flag for shared PTE

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@...cle.com>
Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.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 8bbcccbc5565..699323be7502 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -314,11 +314,13 @@ 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
@@ -360,6 +362,12 @@ 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 e87cb2b80ed3..30e56cbac99b 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 6b7ef495b56d..16083eca720e 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -856,4 +856,9 @@ static inline bool vma_soft_dirty_enabled(struct vm_area_struct *vma)
 	return !(vma->vm_flags & VM_SOFTDIRTY);
 }
 
+static inline bool vma_is_shared(const struct vm_area_struct *vma)
+{
+	return vma->vm_flags & VM_SHARED_PT;
+}
+
 #endif	/* __MM_INTERNAL_H */
-- 
2.34.1