[PATCH] arm: add check for global exclusive monitor

[Vladimir Murzin]

Since ARMv6 new atomic instructions have been introduced:
ldrex/strex. Several implementation are possible based on (1) global
and local exclusive monitors and (2) local exclusive monitor and snoop
unit.

In case of the 2nd option exclusive store operation on uncached
region may be faulty.

Check for availability of the global monitor to provide some hint about
possible issues.

Signed-off-by: Vladimir Murzin <murzin.v at gmail.com>
---
 arch/arm/include/asm/bugs.h |   14 ++++++++++++--
 arch/arm/mm/fault-armv.c    |   43 +++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 55 insertions(+), 2 deletions(-)

diff --git a/arch/arm/include/asm/bugs.h b/arch/arm/include/asm/bugs.h
index a97f1ea..230432e 100644
--- a/arch/arm/include/asm/bugs.h
+++ b/arch/arm/include/asm/bugs.h
@@ -13,9 +13,19 @@
 #ifdef CONFIG_MMU
 extern void check_writebuffer_bugs(void);
 
-#define check_bugs() check_writebuffer_bugs()
+#if  __LINUX_ARM_ARCH__ < 6
+static void check_gmonitor_bugs(void) {};
 #else
-#define check_bugs() do { } while (0)
+extern void check_gmonitor_bugs(void);
+#endif
+
+static inline void check_bugs(void)
+{
+	check_writebuffer_bugs();
+	check_gmonitor_bugs();
+}
+#else
+static inline void check_bugs(void) { }
 #endif
 
 #endif
diff --git a/arch/arm/mm/fault-armv.c b/arch/arm/mm/fault-armv.c
index 7599e26..c12846b 100644
--- a/arch/arm/mm/fault-armv.c
+++ b/arch/arm/mm/fault-armv.c
@@ -206,6 +206,49 @@ void update_mmu_cache(struct vm_area_struct *vma, unsigned long addr,
 			__flush_icache_all();
 	}
 }
+#else
+void __init check_gmonitor_bugs(void)
+{
+	struct page *page;
+	const char *reason;
+	unsigned long res = 1;
+
+	printk(KERN_INFO "CPU: Testing for global monitor: ");
+
+	page = alloc_page(GFP_KERNEL);
+	if (page) {
+		unsigned long *p;
+		pgprot_t prot = __pgprot_modify(PAGE_KERNEL,
+					L_PTE_MT_MASK, L_PTE_MT_UNCACHED);
+
+		p = vmap(&page, 1, VM_IOREMAP, prot);
+
+		if (p) {
+			int temp;
+
+			__asm__ __volatile__(			\
+				"ldrex   %1, [%2]\n"		\
+				"strex   %0, %1, [%2]"		\
+				: "=&r" (res), "=&r" (temp)     \
+				: "r" (p)			\
+				: "cc", "memory");
+
+				reason = "n\\a (atomic ops may be faulty)";
+		} else {
+			reason = "unable to map memory\n";
+		}
+
+		vunmap(p);
+		put_page(page);
+	} else {
+		reason = "unable to grab page\n";
+	}
+
+	if (res)
+		printk("failed, %s\n", reason);
+	else
+		printk("ok\n");
+}
 #endif	/* __LINUX_ARM_ARCH__ < 6 */
 
 /*
-- 
1.7.8.6