linux-kernel - [RFC v2 17/43] PKRAM: provide a way to check if a memory range has preserved pages

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Date:   Tue, 30 Mar 2021 14:35:52 -0700
From:   Anthony Yznaga <anthony.yznaga@...cle.com>
To:     linux-mm@...ck.org, linux-kernel@...r.kernel.org
Cc:     willy@...radead.org, corbet@....net, tglx@...utronix.de,
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Subject: [RFC v2 17/43] PKRAM: provide a way to check if a memory range has preserved pages

When a kernel is loaded for kexec the address ranges where the kexec
segments will be copied to may conflict with pages already set to be
preserved. Provide a way to determine if preserved pages exist in a
specified range.

Signed-off-by: Anthony Yznaga <anthony.yznaga@...cle.com>
---
 include/linux/pkram.h |  2 ++
 mm/pkram.c            | 20 ++++++++++++++++++++
 2 files changed, 22 insertions(+)

diff --git a/include/linux/pkram.h b/include/linux/pkram.h
index 97a7c2ac44a9..977cf45a1bcf 100644
--- a/include/linux/pkram.h
+++ b/include/linux/pkram.h
@@ -104,11 +104,13 @@ int pkram_prepare_save(struct pkram_stream *ps, const char *name,
 void pkram_reserve(void);
 void pkram_cleanup(void);
 void pkram_ban_region(unsigned long start, unsigned long end);
+int pkram_has_preserved_pages(unsigned long start, unsigned long end);
 #else
 #define pkram_reserved_pages 0UL
 static inline void pkram_reserve(void) { }
 static inline void pkram_cleanup(void) { }
 static inline void pkram_ban_region(unsigned long start, unsigned long end) { }
+static inline int pkram_has_preserved_pages(unsigned long start, unsigned long end) { return 0; }
 #endif
 
 #endif /* _LINUX_PKRAM_H */
diff --git a/mm/pkram.c b/mm/pkram.c
index d15be75c1032..dcf84ba785a7 100644
--- a/mm/pkram.c
+++ b/mm/pkram.c
@@ -1668,3 +1668,23 @@ void __init pkram_cleanup(void)
 		pkram_reserved_pages--;
 	}
 }
+
+static int has_preserved_pages_cb(unsigned long base, unsigned long size, void *private)
+{
+	int *has_preserved = (int *)private;
+
+	*has_preserved = 1;
+	return 1;
+}
+
+/*
+ * Check whether the memory range [start, end) contains preserved pages.
+ */
+int pkram_has_preserved_pages(unsigned long start, unsigned long end)
+{
+	int has_preserved = 0;
+
+	pkram_find_preserved(start, end, &has_preserved, has_preserved_pages_cb);
+
+	return has_preserved;
+}
-- 
1.8.3.1