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    SubjectRe: [PATCH 14/18] arm64: erratum: Work around Falkor erratum #E1003 in trampoline code
    On 11/17, Will Deacon wrote:
    > We rely on an atomic swizzling of TTBR1 when transitioning from the entry
    > trampoline to the kernel proper on an exception. We can't rely on this
    > atomicity in the face of Falkor erratum #E1003, so on affected cores we
    > can issue a TLB invalidation prior to jumping into the kernel. There is
    > still the possibility of a TLB conflict here due to conflicting walk
    > cache entries, but this doesn't appear to be the case on these CPUs in
    > practice.
    >
    > Signed-off-by: Will Deacon <will.deacon@arm.com>
    > ---
    > arch/arm64/Kconfig | 17 +++++------------
    > arch/arm64/kernel/entry.S | 8 ++++++++
    > 2 files changed, 13 insertions(+), 12 deletions(-)
    >
    > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
    > index 0df64a6a56d4..f0fcbfc2262e 100644
    > --- a/arch/arm64/Kconfig
    > +++ b/arch/arm64/Kconfig
    > @@ -504,20 +504,13 @@ config CAVIUM_ERRATUM_30115
    > config QCOM_FALKOR_ERRATUM_1003
    > bool "Falkor E1003: Incorrect translation due to ASID change"
    > default y
    > - select ARM64_PAN if ARM64_SW_TTBR0_PAN

    Cool, this sort of complicates the backport of the Kryo MIDR
    update of this errata to stable trees though.

    > diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
    > index a839b94bba05..a600879939ce 100644
    > --- a/arch/arm64/kernel/entry.S
    > +++ b/arch/arm64/kernel/entry.S
    > @@ -941,6 +941,14 @@ __ni_sys_trace:
    > sub \tmp, \tmp, #(SWAPPER_DIR_SIZE + RESERVED_TTBR0_SIZE)
    > bic \tmp, \tmp, #USER_ASID_FLAG
    > msr ttbr1_el1, \tmp
    > +alternative_if ARM64_WORKAROUND_QCOM_FALKOR_E1003

    Shouldn't we put this inside an #ifdef QCOM_FALKOR_ERRATUM_1003
    so that we don't even emit nops in case we have the errata
    disabled? Or did I miss something in the alternatives assembly
    code?

    --
    Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
    a Linux Foundation Collaborative Project

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