[PATCH 3/3] arm64: Add software workaround for Falkor erratum 1041

[Shanker Donthineni <shankerd@codeaurora.org>]

The ARM architecture defines the memory locations that are permitted
to be accessed as the result of a speculative instruction fetch from
an exception level for which all stages of translation are disabled.
Specifically, the core is permitted to speculatively fetch from the
4KB region containing the current program counter and next 4KB.

When translation is changed from enabled to disabled for the running
exception level (SCTLR_ELn[M] changed from a value of 1 to 0), the
Falkor core may errantly speculatively access memory locations outside
of the 4KB region permitted by the architecture. The errant memory
access may lead to one of the following unexpected behaviors.

1) A System Error Interrupt (SEI) being raised by the Falkor core due
   to the errant memory access attempting to access a region of memory
   that is protected by a slave-side memory protection unit.
2) Unpredictable device behavior due to a speculative read from device
   memory. This behavior may only occur if the instruction cache is
   disabled prior to or coincident with translation being changed from
   enabled to disabled.

To avoid the errant behavior, software must execute an ISB immediately
prior to executing the MSR that will change SCTLR_ELn[M] from 1 to 0.

Signed-off-by: Shanker Donthineni <shankerd@codeaurora.org>
---
 Documentation/arm64/silicon-errata.txt |  1 +
 arch/arm64/Kconfig                     | 10 ++++++++++
 arch/arm64/include/asm/assembler.h     | 17 +++++++++++++++++
 arch/arm64/include/asm/cpucaps.h       |  3 ++-
 arch/arm64/kernel/cpu_errata.c         | 16 ++++++++++++++++
 arch/arm64/kernel/efi-entry.S          |  4 ++--
 arch/arm64/kernel/head.S               |  4 ++--
 7 files changed, 50 insertions(+), 5 deletions(-)

diff --git a/Documentation/arm64/silicon-errata.txt b/Documentation/arm64/silicon-errata.txt
index 66e8ce1..704770c0 100644
--- a/Documentation/arm64/silicon-errata.txt
+++ b/Documentation/arm64/silicon-errata.txt
@@ -74,3 +74,4 @@ stable kernels.
 | Qualcomm Tech. | Falkor v1       | E1003           | QCOM_FALKOR_ERRATUM_1003    |
 | Qualcomm Tech. | Falkor v1       | E1009           | QCOM_FALKOR_ERRATUM_1009    |
 | Qualcomm Tech. | QDF2400 ITS     | E0065           | QCOM_QDF2400_ERRATUM_0065   |
+| Qualcomm Tech. | Falkor v{1,2}   | E1041           | QCOM_FALKOR_ERRATUM_1041    |
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 0df64a6..7e933fb 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -539,6 +539,16 @@ config QCOM_QDF2400_ERRATUM_0065
 
 	  If unsure, say Y.
 
+config QCOM_FALKOR_ERRATUM_1041
+	bool "Falkor E1041: Speculative instruction fetches might cause errant memory access"
+	default y
+	help
+	  Falkor CPU may speculatively fetch instructions from an improper
+	  memory location when MMU translation is changed from SCTLR_ELn[M]=1
+	  to SCTLR_ELn[M]=0. Prefix an ISB instruction to fix the problem.
+
+	  If unsure, say Y.
+
 endmenu
 
 
diff --git a/arch/arm64/include/asm/assembler.h b/arch/arm64/include/asm/assembler.h
index b6dfb4f..4c91efb 100644
--- a/arch/arm64/include/asm/assembler.h
+++ b/arch/arm64/include/asm/assembler.h
@@ -30,6 +30,7 @@
 #include <asm/pgtable-hwdef.h>
 #include <asm/ptrace.h>
 #include <asm/thread_info.h>
+#include <asm/alternative.h>
 
 /*
  * Enable and disable interrupts.
@@ -514,6 +515,22 @@
  *   reg: the value to be written.
  */
 	.macro	write_sctlr, eln, reg
+#ifdef CONFIG_QCOM_FALKOR_ERRATUM_1041
+alternative_if ARM64_WORKAROUND_QCOM_FALKOR_E1041
+	tbnz    \reg, #0, 8000f          // enable MMU?
+	isb
+8000:
+alternative_else_nop_endif
+#endif
+	msr	sctlr_\eln, \reg
+	.endm
+
+	.macro	early_write_sctlr, eln, reg
+#ifdef CONFIG_QCOM_FALKOR_ERRATUM_1041
+	tbnz    \reg, #0, 8000f          // enable MMU?
+	isb
+8000:
+#endif
 	msr	sctlr_\eln, \reg
 	.endm
 
diff --git a/arch/arm64/include/asm/cpucaps.h b/arch/arm64/include/asm/cpucaps.h
index 8da6216..7f7a59d 100644
--- a/arch/arm64/include/asm/cpucaps.h
+++ b/arch/arm64/include/asm/cpucaps.h
@@ -40,7 +40,8 @@
 #define ARM64_WORKAROUND_858921			19
 #define ARM64_WORKAROUND_CAVIUM_30115		20
 #define ARM64_HAS_DCPOP				21
+#define ARM64_WORKAROUND_QCOM_FALKOR_E1041	22
 
-#define ARM64_NCAPS				22
+#define ARM64_NCAPS				23
 
 #endif /* __ASM_CPUCAPS_H */
diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c
index 0e27f86..27f9a45 100644
--- a/arch/arm64/kernel/cpu_errata.c
+++ b/arch/arm64/kernel/cpu_errata.c
@@ -179,6 +179,22 @@ static int cpu_enable_trap_ctr_access(void *__unused)
 			   MIDR_CPU_VAR_REV(0, 0)),
 	},
 #endif
+#ifdef CONFIG_QCOM_FALKOR_ERRATUM_1041
+	{
+		.desc = "Qualcomm Technologies Falkor erratum 1041",
+		.capability = ARM64_WORKAROUND_QCOM_FALKOR_E1041,
+		MIDR_RANGE(MIDR_QCOM_FALKOR_V1,
+			MIDR_CPU_VAR_REV(0, 0),
+			MIDR_CPU_VAR_REV(0, 0)),
+	},
+	{
+		.desc = "Qualcomm Technologies Falkor erratum 1041",
+		.capability = ARM64_WORKAROUND_QCOM_FALKOR_E1041,
+		MIDR_RANGE(MIDR_QCOM_FALKOR,
+			MIDR_CPU_VAR_REV(0, 1),
+			MIDR_CPU_VAR_REV(0, 2)),
+	},
+#endif
 #ifdef CONFIG_ARM64_ERRATUM_858921
 	{
 	/* Cortex-A73 all versions */
diff --git a/arch/arm64/kernel/efi-entry.S b/arch/arm64/kernel/efi-entry.S
index acae627..c31be1b 100644
--- a/arch/arm64/kernel/efi-entry.S
+++ b/arch/arm64/kernel/efi-entry.S
@@ -96,14 +96,14 @@ ENTRY(entry)
 	read_sctlr el2, x0
 	bic	x0, x0, #1 << 0	// clear SCTLR.M
 	bic	x0, x0, #1 << 2	// clear SCTLR.C
-	write_sctlr el2, x0
+	early_write_sctlr el2, x0
 	isb
 	b	2f
 1:
 	read_sctlr el1, x0
 	bic	x0, x0, #1 << 0	// clear SCTLR.M
 	bic	x0, x0, #1 << 2	// clear SCTLR.C
-	write_sctlr el1, x0
+	early_write_sctlr el1, x0
 	isb
 2:
 	/* Jump to kernel entry point */
diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
index b8d5b73..9512ce7 100644
--- a/arch/arm64/kernel/head.S
+++ b/arch/arm64/kernel/head.S
@@ -511,7 +511,7 @@ install_el2_stub:
 	mov	x0, #0x0800			// Set/clear RES{1,0} bits
 CPU_BE(	movk	x0, #0x33d0, lsl #16	)	// Set EE and E0E on BE systems
 CPU_LE(	movk	x0, #0x30d0, lsl #16	)	// Clear EE and E0E on LE systems
-	write_sctlr el1, x0
+	early_write_sctlr el1, x0
 
 	/* Coprocessor traps. */
 	mov	x0, #0x33ff
@@ -732,7 +732,7 @@ __primary_switch:
 	 * to take into account by discarding the current kernel mapping and
 	 * creating a new one.
 	 */
-	write_sctlr el1, x20			// disable the MMU
+	early_write_sctlr el1, x20		// disable the MMU
 	isb
 	bl	__create_page_tables		// recreate kernel mapping
 
-- 
Qualcomm Datacenter Technologies, Inc. on behalf of the Qualcomm Technologies, Inc.
Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.