From: Mans Rullgard <mans@mansr.com>
Date: Wed, 30 Jul 2008 08:25:51 +0000 (+0100)
Subject: ARM: NEON L1 cache bug workaround (erratum 451034)
X-Git-Url: http://git.mansr.com/?p=linux-omap;a=commitdiff_plain;h=26023493baf13e0a67fd6cf08d87be5ff6f7c56d

ARM: NEON L1 cache bug workaround (erratum 451034)

On Cortex-A8 r1p0 and r1p1, executing a NEON store with an integer
store in the store buffer, can cause a processor deadlock under
certain conditions.

Executing a DMB instruction before saving NEON/VFP registers and before
return to userspace makes it safe to run code which includes similar
counter-measures.  Userspace code can still trigger the deadlock, so
a different workaround is required to safely run untrusted code.

See ARM Cortex-A8 Errata Notice (PR120-PRDC-008070) for full details.
---

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 8c75840..1172e14 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -1071,6 +1071,22 @@ config NEON
 	  Say Y to include support code for NEON, the ARMv7 Advanced SIMD
 	  Extension.
 
+config NEON_CACHE_BUG
+	bool "NEON L1 cache bug workaround (erratum 451034)"
+	depends on VFPv3
+	help
+          On Cortex-A8 r1p0 and r1p1, executing a NEON store with an integer
+          store in the store buffer, can cause a processor deadlock under
+          certain conditions.
+
+          See ARM Cortex-A8 Errata Notice (PR120-PRDC-008070) for full details.
+
+	  Say Y to include a workaround.
+
+          WARNING: Even with this option enabled, userspace code can trigger
+          the deadlock.  To safely run untrusted code, a different fix is
+          required.
+
 endmenu
 
 menu "Userspace binary formats"
diff --git a/arch/arm/kernel/entry-common.S b/arch/arm/kernel/entry-common.S
index 597ed00..e50094e 100644
--- a/arch/arm/kernel/entry-common.S
+++ b/arch/arm/kernel/entry-common.S
@@ -68,6 +68,10 @@ no_work_pending:
 	/* perform architecture specific actions before user return */
 	arch_ret_to_user r1, lr
 
+#ifdef CONFIG_NEON_CACHE_BUG
+	dmb
+#endif
+
 	@ slow_restore_user_regs
 	ldr	r1, [sp, #S_PSR]		@ get calling cpsr
 	ldr	lr, [sp, #S_PC]!		@ get pc
diff --git a/arch/arm/include/asm/vfpmacros.h b/arch/arm/include/asm/vfpmacros.h
index cccb389..c9d2976 100644
--- a/arch/arm/include/asm/vfpmacros.h
+++ b/arch/arm/include/asm/vfpmacros.h
@@ -32,6 +32,9 @@
 
 	@ write all the working registers out of the VFP
 	.macro	VFPFSTMIA, base, tmp
+#ifdef CONFIG_NEON_CACHE_BUG
+	dmb
+#endif
 #if __LINUX_ARM_ARCH__ < 6
 	STC	p11, cr0, [\base],#33*4		    @ FSTMIAX \base!, {d0-d15}
 #else