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

From: Andre Przywara <andre.przywara@arm.com>
To: Jeremy Linton <jeremy.linton@arm.com>,
	linux-arm-kernel@lists.infradead.org
Cc: catalin.marinas@arm.com, will.deacon@arm.com,
	marc.zyngier@arm.com, suzuki.poulose@arm.com,
	Dave.Martin@arm.com, shankerd@codeaurora.org,
	julien.thierry@arm.com, mlangsdo@redhat.com,
	stefan.wahren@i2e.com, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v5 05/10] arm64: Use firmware to detect CPUs that are not affected by Spectre-v2
Date: Fri, 1 Mar 2019 00:58:19 -0600	[thread overview]
Message-ID: <e1df235f-bcdd-62f0-7b2f-e396df6d9bae@foss.arm.com> (raw)
In-Reply-To: <20190227010544.597579-6-jeremy.linton@arm.com>

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:
> 