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Diffstat (limited to 'arch/x86/include/asm/pgtable_64.h')
-rw-r--r--arch/x86/include/asm/pgtable_64.h8
1 files changed, 7 insertions, 1 deletions
diff --git a/arch/x86/include/asm/pgtable_64.h b/arch/x86/include/asm/pgtable_64.h
index 0b6c4042942a..df1373415f11 100644
--- a/arch/x86/include/asm/pgtable_64.h
+++ b/arch/x86/include/asm/pgtable_64.h
@@ -189,7 +189,7 @@ extern void sync_global_pgds(unsigned long start, unsigned long end);
*
* | ... | 11| 10| 9|8|7|6|5| 4| 3|2| 1|0| <- bit number
* | ... |SW3|SW2|SW1|G|L|D|A|CD|WT|U| W|P| <- bit names
- * | TYPE (59-63) | ~OFFSET (9-58) |0|0|X|X| X| X|X|SD|0| <- swp entry
+ * | TYPE (59-63) | ~OFFSET (9-58) |0|0|X|X| X| X|F|SD|0| <- swp entry
*
* G (8) is aliased and used as a PROT_NONE indicator for
* !present ptes. We need to start storing swap entries above
@@ -197,9 +197,15 @@ extern void sync_global_pgds(unsigned long start, unsigned long end);
* erratum where they can be incorrectly set by hardware on
* non-present PTEs.
*
+ * SD Bits 1-4 are not used in non-present format and available for
+ * special use described below:
+ *
* SD (1) in swp entry is used to store soft dirty bit, which helps us
* remember soft dirty over page migration
*
+ * F (2) in swp entry is used to record when a pagetable is
+ * writeprotected by userfaultfd WP support.
+ *
* Bit 7 in swp entry should be 0 because pmd_present checks not only P,
* but also L and G.
*