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>

1 files changed, 39 insertions, 19 deletions

diff --git a/arch/s390/mm/hugetlbpage.c b/arch/s390/mm/hugetlbpage.c
index b0bd0ae17796..248445f92604 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 @@ static inline pmd_t __pte_to_pmd(pte_t pte)
 		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 @@ static inline pte_t __pmd_to_pte(pmd_t pmd)
 
 	/*
 	 * 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 @@ static inline pte_t __pmd_to_pte(pmd_t pmd)
 			(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;