s390/mm: implement software referenced bits
The last remaining use for the storage key of the s390 architecture
is reference counting. The alternative is to make page table entries
invalid while they are old. On access the fault handler marks the
pte/pmd as young which makes the pte/pmd valid if the access rights
allow read access. The pte/pmd invalidations required for software
managed reference bits cost a bit of performance, on the other hand
the RRBE/RRBM instructions to read and reset the referenced bits are
quite expensive as well.
Reviewed-by: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
diff --git a/arch/s390/mm/hugetlbpage.c b/arch/s390/mm/hugetlbpage.c
index b0bd0ae..248445f 100644
--- a/arch/s390/mm/hugetlbpage.c
+++ b/arch/s390/mm/hugetlbpage.c
@@ -10,19 +10,25 @@
static inline pmd_t __pte_to_pmd(pte_t pte)
{
- int none, prot;
+ int none, young, prot;
pmd_t pmd;
/*
- * Convert encoding pte bits pmd bits
- * .IR.....wdtp ..R...I.....
- * empty .10.....0000 -> ..0...1.....
- * prot-none, clean .11.....0001 -> ..1...1.....
- * prot-none, dirty .10.....0101 -> ..1...1.....
- * read-only, clean .01.....0001 -> ..1...0.....
- * read-only, dirty .01.....0101 -> ..1...0.....
- * read-write, clean .01.....1001 -> ..0...0.....
- * read-write, dirty .00.....1101 -> ..0...0.....
+ * Convert encoding pte bits pmd bits
+ * .IR...wrdytp ..R...I...y.
+ * empty .10...000000 -> ..0...1...0.
+ * prot-none, clean, old .11...000001 -> ..0...1...1.
+ * prot-none, clean, young .11...000101 -> ..1...1...1.
+ * prot-none, dirty, old .10...001001 -> ..0...1...1.
+ * prot-none, dirty, young .10...001101 -> ..1...1...1.
+ * read-only, clean, old .11...010001 -> ..1...1...0.
+ * read-only, clean, young .01...010101 -> ..1...0...1.
+ * read-only, dirty, old .11...011001 -> ..1...1...0.
+ * read-only, dirty, young .01...011101 -> ..1...0...1.
+ * read-write, clean, old .11...110001 -> ..0...1...0.
+ * read-write, clean, young .01...110101 -> ..0...0...1.
+ * read-write, dirty, old .10...111001 -> ..0...1...0.
+ * read-write, dirty, young .00...111101 -> ..0...0...1.
* Huge ptes are dirty by definition, a clean pte is made dirty
* by the conversion.
*/
@@ -31,9 +37,14 @@
if (pte_val(pte) & _PAGE_INVALID)
pmd_val(pmd) |= _SEGMENT_ENTRY_INVALID;
none = (pte_val(pte) & _PAGE_PRESENT) &&
- (pte_val(pte) & _PAGE_INVALID);
- prot = (pte_val(pte) & _PAGE_PROTECT);
- if (prot || none)
+ !(pte_val(pte) & _PAGE_READ) &&
+ !(pte_val(pte) & _PAGE_WRITE);
+ prot = (pte_val(pte) & _PAGE_PROTECT) &&
+ !(pte_val(pte) & _PAGE_WRITE);
+ young = pte_val(pte) & _PAGE_YOUNG;
+ if (none || young)
+ pmd_val(pmd) |= _SEGMENT_ENTRY_YOUNG;
+ if (prot || (none && young))
pmd_val(pmd) |= _SEGMENT_ENTRY_PROTECT;
} else
pmd_val(pmd) = _SEGMENT_ENTRY_INVALID;
@@ -46,11 +57,14 @@
/*
* Convert encoding pmd bits pte bits
- * ..R...I..... .IR.....wdtp
- * empty ..0...1..... -> .10.....0000
- * prot-none, young ..1...1..... -> .10.....0101
- * read-only, young ..1...0..... -> .01.....0101
- * read-write, young ..0...0..... -> .00.....1101
+ * ..R...I...y. .IR...wrdytp
+ * empty ..0...1...0. -> .10...000000
+ * prot-none, old ..0...1...1. -> .10...001001
+ * prot-none, young ..1...1...1. -> .10...001101
+ * read-only, old ..1...1...0. -> .11...011001
+ * read-only, young ..1...0...1. -> .01...011101
+ * read-write, old ..0...1...0. -> .10...111001
+ * read-write, young ..0...0...1. -> .00...111101
* Huge ptes are dirty by definition
*/
if (pmd_present(pmd)) {
@@ -58,11 +72,17 @@
(pmd_val(pmd) & PAGE_MASK);
if (pmd_val(pmd) & _SEGMENT_ENTRY_INVALID)
pte_val(pte) |= _PAGE_INVALID;
- else {
+ if (pmd_prot_none(pmd)) {
+ if (pmd_val(pmd) & _SEGMENT_ENTRY_PROTECT)
+ pte_val(pte) |= _PAGE_YOUNG;
+ } else {
+ pte_val(pte) |= _PAGE_READ;
if (pmd_val(pmd) & _SEGMENT_ENTRY_PROTECT)
pte_val(pte) |= _PAGE_PROTECT;
else
pte_val(pte) |= _PAGE_WRITE;
+ if (pmd_val(pmd) & _SEGMENT_ENTRY_YOUNG)
+ pte_val(pte) |= _PAGE_YOUNG;
}
} else
pte_val(pte) = _PAGE_INVALID;