Subject: [PATCH v7 2/4] PM: hibernate: make direct map manipulations more explicit

From: Mike Rapoport <[email-masked]>
Date: Mon, 9 Nov 2020 21:21:26 +0200

From: Mike Rapoport <[email-masked]>

When DEBUG_PAGEALLOC or ARCH_HAS_SET_DIRECT_MAP is enabled a page may be
not present in the direct map and has to be explicitly mapped before it
could be copied.

Introduce hibernate_map_page() and hibernation_unmap_page() that will
explicitly use set_direct_map_{default,invalid}_noflush() for
ARCH_HAS_SET_DIRECT_MAP case and debug_pagealloc_{map,unmap}_pages() for
DEBUG_PAGEALLOC case.

The remapping of the pages in safe_copy_page() presumes that it only
changes protection bits in an existing PTE and so it is safe to ignore
return value of set_direct_map_{default,invalid}_noflush().

Still, add a pr_warn() so that future changes in set_memory APIs will not
silently break hibernation.

Signed-off-by: Mike Rapoport <[email-masked]>
Acked-by: Rafael J. Wysocki <[email-masked]>
Reviewed-by: David Hildenbrand <[email-masked]>
Acked-by: Kirill A. Shutemov <[email-masked]>
Acked-by: Vlastimil Babka <[email-masked]>
---
 include/linux/mm.h      | 12 ------------
 kernel/power/snapshot.c | 38 ++++++++++++++++++++++++++++++++++++--
 2 files changed, 36 insertions(+), 14 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index bb8c70178f4e..e198b938f5c5 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2927,16 +2927,6 @@ static inline bool debug_pagealloc_enabled_static(void)
 #if defined(CONFIG_DEBUG_PAGEALLOC) || defined(CONFIG_ARCH_HAS_SET_DIRECT_MAP)
 extern void __kernel_map_pages(struct page *page, int numpages, int enable);
 
-/*
- * When called in DEBUG_PAGEALLOC context, the call should most likely be
- * guarded by debug_pagealloc_enabled() or debug_pagealloc_enabled_static()
- */
-static inline void
-kernel_map_pages(struct page *page, int numpages, int enable)
-{
-	__kernel_map_pages(page, numpages, enable);
-}
-
 static inline void debug_pagealloc_map_pages(struct page *page, int numpages)
 {
 	if (debug_pagealloc_enabled_static())
@@ -2953,8 +2943,6 @@ static inline void debug_pagealloc_unmap_pages(struct page *page, int numpages)
 extern bool kernel_page_present(struct page *page);
 #endif	/* CONFIG_HIBERNATION */
 #else	/* CONFIG_DEBUG_PAGEALLOC || CONFIG_ARCH_HAS_SET_DIRECT_MAP */
-static inline void
-kernel_map_pages(struct page *page, int numpages, int enable) {}
 static inline void debug_pagealloc_map_pages(struct page *page, int numpages) {}
 static inline void debug_pagealloc_unmap_pages(struct page *page, int numpages) {}
 #ifdef CONFIG_HIBERNATION
diff --git a/kernel/power/snapshot.c b/kernel/power/snapshot.c
index 46b1804c1ddf..d848377dd8dc 100644
--- a/kernel/power/snapshot.c
+++ b/kernel/power/snapshot.c
@@ -76,6 +76,40 @@ static inline void hibernate_restore_protect_page(void *page_address) {}
 static inline void hibernate_restore_unprotect_page(void *page_address) {}
 #endif /* CONFIG_STRICT_KERNEL_RWX  && CONFIG_ARCH_HAS_SET_MEMORY */
 
+
+/*
+ * The calls to set_direct_map_*() should not fail because remapping a page
+ * here means that we only update protection bits in an existing PTE.
+ * It is still worth to have a warning here if something changes and this
+ * will no longer be the case.
+ */
+static inline void hibernate_map_page(struct page *page)
+{
+	if (IS_ENABLED(CONFIG_ARCH_HAS_SET_DIRECT_MAP)) {
+		int ret = set_direct_map_default_noflush(page);
+
+		if (ret)
+			pr_warn_once("Failed to remap page\n");
+	} else {
+		debug_pagealloc_map_pages(page, 1);
+	}
+}
+
+static inline void hibernate_unmap_page(struct page *page)
+{
+	if (IS_ENABLED(CONFIG_ARCH_HAS_SET_DIRECT_MAP)) {
+		unsigned long addr = (unsigned long)page_address(page);
+		int ret  = set_direct_map_invalid_noflush(page);
+
+		if (ret)
+			pr_warn_once("Failed to remap page\n");
+
+		flush_tlb_kernel_range(addr, addr + PAGE_SIZE);
+	} else {
+		debug_pagealloc_unmap_pages(page, 1);
+	}
+}
+
 static int swsusp_page_is_free(struct page *);
 static void swsusp_set_page_forbidden(struct page *);
 static void swsusp_unset_page_forbidden(struct page *);
@@ -1355,9 +1389,9 @@ static void safe_copy_page(void *dst, struct page *s_page)
 	if (kernel_page_present(s_page)) {
 		do_copy_page(dst, page_address(s_page));
 	} else {
-		kernel_map_pages(s_page, 1, 1);
+		hibernate_map_page(s_page);
 		do_copy_page(dst, page_address(s_page));
-		kernel_map_pages(s_page, 1, 0);
+		hibernate_unmap_page(s_page);
 	}
 }
 
-- 
2.28.0