[PATCH v3 2/2] arm64: Add software workaround for Falkor erratum 1041

From: Shanker Donthineni
Date: Sun Nov 12 2017 - 20:42:53 EST

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 4K and next 4K.

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.

The conditions leading to this erratum will not occur when either of the
following occur:
1) A higher exception level disables translation of a lower exception level
(e.g. EL2 changing SCTLR_EL1[M] from a value of 1 to 0).
2) An exception level disabling its stage-1 translation if its stage-2
translation is enabled (e.g. EL1 changing SCTLR_EL1[M] from a value of 1
to 0 when HCR_EL2[VM] has a value of 1).

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@xxxxxxxxxxxxxx>
---
Changes since v1:
Apply the workaround where it's required.
Changes since v2:
Repost the corrected patches.

Documentation/arm64/silicon-errata.txt | 1 +
arch/arm64/Kconfig | 10 ++++++++++
arch/arm64/include/asm/assembler.h | 19 +++++++++++++++++++
arch/arm64/include/asm/cpucaps.h | 3 ++-
arch/arm64/kernel/cpu-reset.S | 1 +
arch/arm64/kernel/cpu_errata.c | 16 ++++++++++++++++
arch/arm64/kernel/efi-entry.S | 2 ++
arch/arm64/kernel/head.S | 1 +
arch/arm64/kernel/relocate_kernel.S | 1 +
arch/arm64/kvm/hyp-init.S | 1 +
10 files changed, 54 insertions(+), 1 deletion(-)

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..8f73eac 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_E1041
+ 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 d58a625..dd9cec5 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.
@@ -499,4 +500,22 @@
#endif
.endm

+/**
+ * Errata workaround prior to disable MMU. Insert an ISB immediately prior
+ * to executing the MSR that will change SCTLR_ELn[M] from a value of 1 to 0.
+ */
+ .macro pre_disable_mmu_workaround
+#ifdef CONFIG_QCOM_FALKOR_ERRATUM_E1041
+alternative_if ARM64_WORKAROUND_QCOM_FALKOR_E1041
+ isb
+alternative_else_nop_endif
+#endif
+ .endm
+
+ .macro pre_disable_mmu_early_workaround
+#ifdef CONFIG_QCOM_FALKOR_ERRATUM_E1041
+ isb
+#endif
+ .endm
+
#endif /* __ASM_ASSEMBLER_H */
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-reset.S b/arch/arm64/kernel/cpu-reset.S
index 65f42d2..2a752cb 100644
--- a/arch/arm64/kernel/cpu-reset.S
+++ b/arch/arm64/kernel/cpu-reset.S
@@ -37,6 +37,7 @@ ENTRY(__cpu_soft_restart)
mrs x12, sctlr_el1
ldr x13, =SCTLR_ELx_FLAGS
bic x12, x12, x13
+ pre_disable_mmu_workaround
msr sctlr_el1, x12
isb

diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c
index 0e27f86..2fd1938 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_E1041
+ {
+ .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 4e6ad35..dc675ba 100644
--- a/arch/arm64/kernel/efi-entry.S
+++ b/arch/arm64/kernel/efi-entry.S
@@ -96,6 +96,7 @@ ENTRY(entry)
mrs x0, sctlr_el2
bic x0, x0, #1 << 0 // clear SCTLR.M
bic x0, x0, #1 << 2 // clear SCTLR.C
+ pre_disable_mmu_early_workaround
msr sctlr_el2, x0
isb
b 2f
@@ -103,6 +104,7 @@ ENTRY(entry)
mrs x0, sctlr_el1
bic x0, x0, #1 << 0 // clear SCTLR.M
bic x0, x0, #1 << 2 // clear SCTLR.C
+ pre_disable_mmu_early_workaround
msr sctlr_el1, x0
isb
2:
diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
index 0b243ec..a807fca 100644
--- a/arch/arm64/kernel/head.S
+++ b/arch/arm64/kernel/head.S
@@ -732,6 +732,7 @@ __primary_switch:
* to take into account by discarding the current kernel mapping and
* creating a new one.
*/
+ pre_disable_mmu_early_workaround
msr sctlr_el1, x20 // disable the MMU
isb
bl __create_page_tables // recreate kernel mapping
diff --git a/arch/arm64/kernel/relocate_kernel.S b/arch/arm64/kernel/relocate_kernel.S
index ce704a4..f407e42 100644
--- a/arch/arm64/kernel/relocate_kernel.S
+++ b/arch/arm64/kernel/relocate_kernel.S
@@ -45,6 +45,7 @@ ENTRY(arm64_relocate_new_kernel)
mrs x0, sctlr_el2
ldr x1, =SCTLR_ELx_FLAGS
bic x0, x0, x1
+ pre_disable_mmu_workaround
msr sctlr_el2, x0
isb
1:
diff --git a/arch/arm64/kvm/hyp-init.S b/arch/arm64/kvm/hyp-init.S
index 3f96155..870828c 100644
--- a/arch/arm64/kvm/hyp-init.S
+++ b/arch/arm64/kvm/hyp-init.S
@@ -151,6 +151,7 @@ reset:
mrs x5, sctlr_el2
ldr x6, =SCTLR_ELx_FLAGS
bic x5, x5, x6 // Clear SCTL_M and etc
+ pre_disable_mmu_workaround
msr sctlr_el2, x5
isb

--
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