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    SubjectRe: [PATCH v5 05/10] arm64: Use firmware to detect CPUs that are not affected by Spectre-v2
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    Hi,

    On 2/26/19 7:05 PM, Jeremy Linton wrote:
    > From: Marc Zyngier <marc.zyngier@arm.com>
    >
    > The SMCCC ARCH_WORKAROUND_1 service can indicate that although the
    > firmware knows about the Spectre-v2 mitigation, this particular
    > CPU is not vulnerable, and it is thus not necessary to call
    > the firmware on this CPU.
    >
    > Let's use this information to our benefit.

    Yes, that matches the firmware interface description.

    > Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
    > Signed-off-by: Jeremy Linton <jeremy.linton@arm.com>

    Reviewed-by: Andre Przywara <andre.przywara@arm.com>

    Cheers,
    Andre.

    > ---
    > arch/arm64/kernel/cpu_errata.c | 32 +++++++++++++++++++++++---------
    > 1 file changed, 23 insertions(+), 9 deletions(-)
    >
    > diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c
    > index c8972255b365..77f021e78a28 100644
    > --- a/arch/arm64/kernel/cpu_errata.c
    > +++ b/arch/arm64/kernel/cpu_errata.c
    > @@ -230,22 +230,36 @@ static int detect_harden_bp_fw(void)
    > case PSCI_CONDUIT_HVC:
    > arm_smccc_1_1_hvc(ARM_SMCCC_ARCH_FEATURES_FUNC_ID,
    > ARM_SMCCC_ARCH_WORKAROUND_1, &res);
    > - if ((int)res.a0 < 0)
    > + switch ((int)res.a0) {
    > + case 1:
    > + /* Firmware says we're just fine */
    > + return 0;
    > + case 0:
    > + cb = call_hvc_arch_workaround_1;
    > + /* This is a guest, no need to patch KVM vectors */
    > + smccc_start = NULL;
    > + smccc_end = NULL;
    > + break;
    > + default:
    > return -1;
    > - cb = call_hvc_arch_workaround_1;
    > - /* This is a guest, no need to patch KVM vectors */
    > - smccc_start = NULL;
    > - smccc_end = NULL;
    > + }
    > break;
    >
    > case PSCI_CONDUIT_SMC:
    > arm_smccc_1_1_smc(ARM_SMCCC_ARCH_FEATURES_FUNC_ID,
    > ARM_SMCCC_ARCH_WORKAROUND_1, &res);
    > - if ((int)res.a0 < 0)
    > + switch ((int)res.a0) {
    > + case 1:
    > + /* Firmware says we're just fine */
    > + return 0;
    > + case 0:
    > + cb = call_smc_arch_workaround_1;
    > + smccc_start = __smccc_workaround_1_smc_start;
    > + smccc_end = __smccc_workaround_1_smc_end;
    > + break;
    > + default:
    > return -1;
    > - cb = call_smc_arch_workaround_1;
    > - smccc_start = __smccc_workaround_1_smc_start;
    > - smccc_end = __smccc_workaround_1_smc_end;
    > + }
    > break;
    >
    > default:
    >

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