[XTENSA] Add support for cache-aliasing

Add support for processors that have cache-aliasing issues, such as
the Stretch S5000 processor. Cache-aliasing means that the size of
the cache (for one way) is larger than the page size, thus, a page
can end up in several places in cache depending on the virtual to
physical translation. The method used here is to map a user page
temporarily through the auto-refill way 0 and of of the DTLB.
We probably will want to revisit this issue and use a better
approach with kmap/kunmap.

Signed-off-by: Chris Zankel <chris@zankel.net>

1 files changed, 71 insertions, 4 deletions

diff --git a/arch/xtensa/kernel/entry.S b/arch/xtensa/kernel/entry.S
index 65741e3..91a689e 100644
--- a/arch/xtensa/kernel/entry.S
+++ b/arch/xtensa/kernel/entry.S
@@ -7,7 +7,7 @@
  * License.  See the file "COPYING" in the main directory of this archive
  * for more details.
  *
- * Copyright (C) 2004-2005 by Tensilica Inc.
+ * Copyright (C) 2004-2007 by Tensilica Inc.
  *
  * Chris Zankel <chris@zankel.net>
  *
@@ -169,7 +169,7 @@ _user_exception:
 	 * We have to save all registers up to the first '1' from
 	 * the right, except the current frame (bit 0).
 	 * Assume a2 is:  001001000110001
-	 * All regiser frames starting from the top fiel to the marked '1'
+	 * All register frames starting from the top field to the marked '1'
 	 * must be saved.
 	 */
 
@@ -1590,7 +1590,7 @@ ENTRY(fast_second_level_miss)
 	 * The messy computation for 'pteval' above really simplifies
 	 * into the following:
 	 *
-	 * pteval = ((pmdval - PAGE_OFFSET) & PAGE_MASK) | PAGE_KERNEL
+	 * pteval = ((pmdval - PAGE_OFFSET) & PAGE_MASK) | PAGE_DIRECTORY
 	 */
 
 	movi	a1, -PAGE_OFFSET
@@ -1602,7 +1602,7 @@ ENTRY(fast_second_level_miss)
 	or	a0, a0, a1		# ... | PAGE_DIRECTORY
 
 	/*
-	 * We utilize all three wired-ways (7-9( to hold pmd translations.
+	 * We utilize all three wired-ways (7-9) to hold pmd translations.
 	 * Memory regions are mapped to the DTLBs according to bits 28 and 29.
 	 * This allows to map the three most common regions to three different
 	 * DTLBs:
@@ -1652,6 +1652,73 @@ ENTRY(fast_second_level_miss)
 9:	l32i	a0, a1, TASK_ACTIVE_MM	# unlikely case mm == 0
 	j	8b
 
+#if (DCACHE_WAY_SIZE > PAGE_SIZE)
+
+2:	/* Special case for cache aliasing.
+	 * We (should) only get here if a clear_user_page, copy_user_page
+	 * or the aliased cache flush functions got preemptively interrupted 
+	 * by another task. Re-establish temporary mapping to the 
+	 * TLBTEMP_BASE areas.
+	 */
+
+	/* We shouldn't be in a double exception */
+
+	l32i	a0, a2, PT_DEPC
+	bgeui	a0, VALID_DOUBLE_EXCEPTION_ADDRESS, 2f
+
+	/* Make sure the exception originated in the special functions */
+
+	movi	a0, __tlbtemp_mapping_start
+	rsr	a3, EPC_1
+	bltu	a3, a0, 2f
+	movi	a0, __tlbtemp_mapping_end
+	bgeu	a3, a0, 2f
+
+	/* Check if excvaddr was in one of the TLBTEMP_BASE areas. */
+
+	movi	a3, TLBTEMP_BASE_1
+	rsr	a0, EXCVADDR
+	bltu	a0, a3, 2f
+
+	addi	a1, a0, -(2 << (DCACHE_ALIAS_ORDER + PAGE_SHIFT))
+	bgeu	a1, a3, 2f
+
+	/* Check if we have to restore an ITLB mapping. */
+
+	movi	a1, __tlbtemp_mapping_itlb
+	rsr	a3, EPC_1
+	sub	a3, a3, a1
+
+	/* Calculate VPN */
+
+	movi	a1, PAGE_MASK
+	and	a1, a1, a0
+
+	/* Jump for ITLB entry */
+
+	bgez	a3, 1f
+
+	/* We can use up to two TLBTEMP areas, one for src and one for dst. */
+
+	extui	a3, a0, PAGE_SHIFT + DCACHE_ALIAS_ORDER, 1
+	add	a1, a3, a1
+
+	/* PPN is in a6 for the first TLBTEMP area and in a7 for the second. */
+
+	mov	a0, a6
+	movnez	a0, a7, a3
+	j	3b
+
+	/* ITLB entry. We only use dst in a6. */
+
+1:	witlb	a6, a1
+	isync
+	j	4b
+
+
+#endif	// DCACHE_WAY_SIZE > PAGE_SIZE
+
+
 2:	/* Invalid PGD, default exception handling */
 
 	movi	a3, exc_table