MIPS: Implement Read Inhibit/eXecute Inhibit

The SmartMIPS ASE specifies how Read Inhibit (RI) and eXecute Inhibit
(XI) bits in the page tables work.  The upper two bits of EntryLo{0,1}
are RI and XI when the feature is enabled in the PageGrain register.
SmartMIPS only covers 32-bit systems.  Cavium Octeon+ extends this to
64-bit systems by continuing to place the RI and XI bits in the top of
EntryLo even when EntryLo is 64-bits wide.

Because we need to carry the RI and XI bits in the PTE, the layout of
the PTE is changed.  There is a two instruction overhead in the TLB
refill hot path to get the EntryLo bits into the proper position.
Also the TLB load exception has to probe the TLB to check if RI or XI
caused the exception.

Also of note is that the layout of the PTE bits is done at compile and
runtime rather than statically.  In the 32-bit case this allows for
the same number of PFN bits as before the patch as the _PAGE_HUGE is
not supported in 32-bit kernels (we have _PAGE_NO_EXEC and
_PAGE_NO_READ instead of _PAGE_READ and _PAGE_HUGE).

The patch is tested on Cavium Octeon+, but should also work on 32-bit
systems with the Smart-MIPS ASE.

Signed-off-by: David Daney <ddaney@caviumnetworks.com>
To: linux-mips@linux-mips.org
Patchwork: http://patchwork.linux-mips.org/patch/952/
Patchwork: http://patchwork.linux-mips.org/patch/956/
Patchwork: http://patchwork.linux-mips.org/patch/962/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

1 files changed, 16 insertions, 10 deletions

diff --git a/arch/mips/include/asm/pgtable.h b/arch/mips/include/asm/pgtable.h
index 02335fda9e77..93598ba01355 100644
--- a/arch/mips/include/asm/pgtable.h
+++ b/arch/mips/include/asm/pgtable.h
@@ -22,23 +22,24 @@ struct mm_struct;
 struct vm_area_struct;
 
 #define PAGE_NONE	__pgprot(_PAGE_PRESENT | _CACHE_CACHABLE_NONCOHERENT)
-#define PAGE_SHARED	__pgprot(_PAGE_PRESENT | _PAGE_READ | _PAGE_WRITE | \
+#define PAGE_SHARED	__pgprot(_PAGE_PRESENT | _PAGE_WRITE | (kernel_uses_smartmips_rixi ? 0 : _PAGE_READ) | \
 				 _page_cachable_default)
-#define PAGE_COPY	__pgprot(_PAGE_PRESENT | _PAGE_READ | \
-				 _page_cachable_default)
-#define PAGE_READONLY	__pgprot(_PAGE_PRESENT | _PAGE_READ | \
+#define PAGE_COPY	__pgprot(_PAGE_PRESENT | (kernel_uses_smartmips_rixi ? 0 : _PAGE_READ) | \
+				 (kernel_uses_smartmips_rixi ?  _PAGE_NO_EXEC : 0) | _page_cachable_default)
+#define PAGE_READONLY	__pgprot(_PAGE_PRESENT | (kernel_uses_smartmips_rixi ? 0 : _PAGE_READ) | \
 				 _page_cachable_default)
 #define PAGE_KERNEL	__pgprot(_PAGE_PRESENT | __READABLE | __WRITEABLE | \
 				 _PAGE_GLOBAL | _page_cachable_default)
-#define PAGE_USERIO	__pgprot(_PAGE_PRESENT | _PAGE_READ | _PAGE_WRITE | \
+#define PAGE_USERIO	__pgprot(_PAGE_PRESENT | (kernel_uses_smartmips_rixi ? 0 : _PAGE_READ) | _PAGE_WRITE | \
 				 _page_cachable_default)
 #define PAGE_KERNEL_UNCACHED __pgprot(_PAGE_PRESENT | __READABLE | \
 			__WRITEABLE | _PAGE_GLOBAL | _CACHE_UNCACHED)
 
 /*
- * MIPS can't do page protection for execute, and considers that the same like
- * read. Also, write permissions imply read permissions. This is the closest
- * we can get by reasonable means..
+ * If _PAGE_NO_EXEC is not defined, we can't do page protection for
+ * execute, and consider it to be the same as read. Also, write
+ * permissions imply read permissions. This is the closest we can get
+ * by reasonable means..
  */
 
 /*
@@ -298,8 +299,13 @@ static inline pte_t pte_mkdirty(pte_t pte)
 static inline pte_t pte_mkyoung(pte_t pte)
 {
 	pte_val(pte) |= _PAGE_ACCESSED;
-	if (pte_val(pte) & _PAGE_READ)
-		pte_val(pte) |= _PAGE_SILENT_READ;
+	if (kernel_uses_smartmips_rixi) {
+		if (!(pte_val(pte) & _PAGE_NO_READ))
+			pte_val(pte) |= _PAGE_SILENT_READ;
+	} else {
+		if (pte_val(pte) & _PAGE_READ)
+			pte_val(pte) |= _PAGE_SILENT_READ;
+	}
 	return pte;
 }