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SubjectRe: [v3,2/2] arm64: Add software workaround for Falkor erratum 1041
On Sun, 12 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 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@codeaurora.org>
> ---
> 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
>
>

I applied the V3 of errtum 1041 patches to Ubuntu Artful 4.13 kernel and
ran the stress-ng and VM create/stop/restart testing like I did on the
previous version of this patch series. Tests successfully ran on qdf2400
platform, I did not observe any regressions on the Artful 4.13 kernel.

Tested-by: Manoj Iyer <manoj.iyer@canonical.com>

--
============================
Manoj Iyer
Ubuntu/Canonical
ARM Servers - Cloud
============================

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