ARM: ensure C page table setup code follows assembly code

Fix a long standing bug where, for ARMv6+, we don't fully ensure that
the C code sets the same cache policy as the assembly code.  This was
introduced partially by commit 11179d8ca28d ([ARM] 4497/1: Only allow
safe cache configurations on ARMv6 and later) and also by adding SMP
support.

This patch sets the default cache policy based on the flags used by the
assembly code, and then ensures that when a cache policy command line
argument is used, we verify that on ARMv6, it matches the initial setup.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

1 files changed, 47 insertions, 16 deletions

diff --git a/arch/arm/mm/mmu.c b/arch/arm/mm/mmu.c
index 9c8fec02c274..92df149c88a8 100644
--- a/arch/arm/mm/mmu.c
+++ b/arch/arm/mm/mmu.c
@@ -118,27 +118,49 @@ static struct cachepolicy cache_policies[] __initdata = {
 
 #ifdef CONFIG_CPU_CP15
 /*
- * These are useful for identifying cache coherency
- * problems by allowing the cache or the cache and
- * writebuffer to be turned off.  (Note: the write
- * buffer should not be on and the cache off).
+ * Initialise the cache_policy variable with the initial state specified
+ * via the "pmd" value.  This is used to ensure that on ARMv6 and later,
+ * the C code sets the page tables up with the same policy as the head
+ * assembly code, which avoids an illegal state where the TLBs can get
+ * confused.  See comments in early_cachepolicy() for more information.
  */
-static int __init early_cachepolicy(char *p)
+void __init init_default_cache_policy(unsigned long pmd)
 {
-	unsigned long cr = get_cr();
 	int i;
 
+	pmd &= PMD_SECT_TEX(1) | PMD_SECT_BUFFERABLE | PMD_SECT_CACHEABLE;
+
+	for (i = 0; i < ARRAY_SIZE(cache_policies); i++)
+		if (cache_policies[i].pmd == pmd) {
+			cachepolicy = i;
+			break;
+		}
+
+	if (i == ARRAY_SIZE(cache_policies))
+		pr_err("ERROR: could not find cache policy\n");
+}
+
+/*
+ * These are useful for identifying cache coherency problems by allowing
+ * the cache or the cache and writebuffer to be turned off.  (Note: the
+ * write buffer should not be on and the cache off).
+ */
+static int __init early_cachepolicy(char *p)
+{
+	int i, selected = -1;
+
 	for (i = 0; i < ARRAY_SIZE(cache_policies); i++) {
 		int len = strlen(cache_policies[i].policy);
 
 		if (memcmp(p, cache_policies[i].policy, len) == 0) {
-			cachepolicy = i;
-			cr = __clear_cr(cache_policies[i].cr_mask);
+			selected = i;
 			break;
 		}
 	}
-	if (i == ARRAY_SIZE(cache_policies))
-		printk(KERN_ERR "ERROR: unknown or unsupported cache policy\n");
+
+	if (selected == -1)
+		pr_err("ERROR: unknown or unsupported cache policy\n");
+
 	/*
 	 * This restriction is partly to do with the way we boot; it is
 	 * unpredictable to have memory mapped using two different sets of
@@ -146,12 +168,18 @@ static int __init early_cachepolicy(char *p)
 	 * change these attributes once the initial assembly has setup the
 	 * page tables.
 	 */
-	if (cpu_architecture() >= CPU_ARCH_ARMv6) {
-		printk(KERN_WARNING "Only cachepolicy=writeback supported on ARMv6 and later\n");
-		cachepolicy = CPOLICY_WRITEBACK;
+	if (cpu_architecture() >= CPU_ARCH_ARMv6 && selected != cachepolicy) {
+		pr_warn("Only cachepolicy=%s supported on ARMv6 and later\n",
+			cache_policies[cachepolicy].policy);
+		return 0;
+	}
+
+	if (selected != cachepolicy) {
+		unsigned long cr = __clear_cr(cache_policies[selected].cr_mask);
+		cachepolicy = selected;
+		flush_cache_all();
+		set_cr(cr);
 	}
-	flush_cache_all();
-	set_cr(cr);
 	return 0;
 }
 early_param("cachepolicy", early_cachepolicy);
@@ -385,8 +413,11 @@ static void __init build_mem_type_table(void)
 			cachepolicy = CPOLICY_WRITEBACK;
 		ecc_mask = 0;
 	}
-	if (is_smp())
+
+	if (is_smp() && cachepolicy != CPOLICY_WRITEALLOC) {
+		pr_warn("Forcing write-allocate cache policy for SMP\n");
 		cachepolicy = CPOLICY_WRITEALLOC;
+	}
 
 	/*
 	 * Strip out features not present on earlier architectures.