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

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Date:   Wed,  6 May 2020 17:41:43 -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,
        mingo@...hat.com, bp@...en8.de, x86@...nel.org, hpa@...or.com,
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Subject: [RFC 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            | 25 +++++++++++++++++++++++++
 2 files changed, 27 insertions(+)

diff --git a/include/linux/pkram.h b/include/linux/pkram.h
index 1ba48442ef8e..1cd518843d7a 100644
--- a/include/linux/pkram.h
+++ b/include/linux/pkram.h
@@ -70,11 +70,13 @@ extern unsigned long pkram_reserved_pages;
 void pkram_reserve(void);
 void pkram_free_pgt(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_free_pgt(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 60863c8ecbab..0aaaf9b79682 100644
--- a/mm/pkram.c
+++ b/mm/pkram.c
@@ -1499,3 +1499,28 @@ phys_addr_t __init_memblock pkram_memblock_find_in_range(phys_addr_t start,
 
 	return st.retval;
 }
+
+static int pkram_has_preserved_pages_cb(struct pkram_pg_state *st, unsigned long base, unsigned long size)
+{
+	st->retval = 1;
+	return 1;
+}
+
+/*
+ * Check whether the memory range [start, end) contains preserved pages.
+ */
+int pkram_has_preserved_pages(unsigned long start, unsigned long end)
+{
+	struct pkram_pg_state st = {
+		.range_cb = pkram_has_preserved_pages_cb,
+		.min_addr = start,
+		.max_addr = end,
+	};
+
+	if (!pkram_pgd)
+		return 0;
+
+	pkram_walk_pgt_rev(&st, pkram_pgd);
+
+	return st.retval;
+}
-- 
2.13.3