Re: [3/3] arm64: Add software workaround for Falkor erratum 1041
From: Manoj Iyer
Date: Wed Nov 08 2017 - 14:06:08 EST
On Thu, 2 Nov 2017, Shanker Donthineni wrote:
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@xxxxxxxxxxxxxx>
---
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
I applied the 3 patches to Ubuntu 4.13.0-16-generic (Artful) kernel and
ran stress-ng cpu tests on QDF2400 server as follows:
sudo ./stress-ng --pathological -v --cpu 100 --cpu-load 80 --cpu-method
all --cpu-online 500 --matrix 100 --matrix-method all --matrix-size 8192
--vm 10 --vm-hang 10 --vm-method all --switch 100 --numa 100
Where stress-ng would spawn N workers and test cpu offline/online, perform
matrix operations, do rapid context switchs, and anonymous mmaps. Although
I was not able to reproduce the erratum on the stock 4.13 kernel using the
same test case, the patched kernel did not seem to introduce any
regressions either. I ran the stress-ng tests for over 8hrs found the
system to be stable.
Tested-by: Manoj Iyer <manoj.iyer@xxxxxxxxxxxxx>
Regards
--
============================
Manoj Iyer
Ubuntu/Canonical
ARM Servers - Cloud
============================