linux-kernel - [PATCH V8 33/44] memremap_pages: Introduce pgmap_protection

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Date:   Thu, 27 Jan 2022 09:54:54 -0800
From:   ira.weiny@...el.com
To:     Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Dan Williams <dan.j.williams@...el.com>
Cc:     Ira Weiny <ira.weiny@...el.com>, Fenghua Yu <fenghua.yu@...el.com>,
        Rick Edgecombe <rick.p.edgecombe@...el.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH V8 33/44] memremap_pages: Introduce pgmap_protection_available()

From: Ira Weiny <ira.weiny@...el.com>

Users will need to specify that they want their dev_pagemap pages
protected by specifying a flag in (struct dev_pagemap)->flags.  However,
it is more efficient to know if that protection is available prior to
requesting it and failing the mapping.

Define pgmap_protection_available() for users to check if protection is
available to be used.  The name of pgmap_protection_available() was
specifically chosen to isolate the implementation of the protection from
higher level users.  However, the current implementation simply calls
pks_available() to determine if it can support protection.

It was considered to have users specify the flag and check if the
dev_pagemap object returned was protected or not.  But this was
considered less efficient than a direct check beforehand.

Signed-off-by: Ira Weiny <ira.weiny@...el.com>

---
Changes for V8
	Split this out to it's own patch.
	s/pgmap_protection_enabled/pgmap_protection_available
---
 include/linux/mm.h | 13 +++++++++++++
 mm/memremap.c      | 11 +++++++++++
 2 files changed, 24 insertions(+)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index e1a84b1e6787..2ae99bee6e82 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1143,6 +1143,19 @@ static inline bool is_pci_p2pdma_page(const struct page *page)
 		page->pgmap->type == MEMORY_DEVICE_PCI_P2PDMA;
 }
 
+#ifdef CONFIG_DEVMAP_ACCESS_PROTECTION
+
+bool pgmap_protection_available(void);
+
+#else
+
+static inline bool pgmap_protection_available(void)
+{
+	return false;
+}
+
+#endif /* CONFIG_DEVMAP_ACCESS_PROTECTION */
+
 /* 127: arbitrary random number, small enough to assemble well */
 #define folio_ref_zero_or_close_to_overflow(folio) \
 	((unsigned int) folio_ref_count(folio) + 127u <= 127u)
diff --git a/mm/memremap.c b/mm/memremap.c
index 6aa5f0c2d11f..c13b3b8a0048 100644
--- a/mm/memremap.c
+++ b/mm/memremap.c
@@ -6,6 +6,7 @@
 #include <linux/memory_hotplug.h>
 #include <linux/mm.h>
 #include <linux/pfn_t.h>
+#include <linux/pkeys.h>
 #include <linux/swap.h>
 #include <linux/mmzone.h>
 #include <linux/swapops.h>
@@ -63,6 +64,16 @@ static void devmap_managed_enable_put(struct dev_pagemap *pgmap)
 }
 #endif /* CONFIG_DEV_PAGEMAP_OPS */
 
+#ifdef CONFIG_DEVMAP_ACCESS_PROTECTION
+
+bool pgmap_protection_available(void)
+{
+	return pks_available();
+}
+EXPORT_SYMBOL_GPL(pgmap_protection_available);
+
+#endif /* CONFIG_DEVMAP_ACCESS_PROTECTION */
+
 static void pgmap_array_delete(struct range *range)
 {
 	xa_store_range(&pgmap_array, PHYS_PFN(range->start), PHYS_PFN(range->end),
-- 
2.31.1