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To:     Will Deacon <will.deacon@arm.com>,
        Jayachandran C <jnair@caviumnetworks.com>
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        catalin.marinas@arm.com, linux-kernel@vger.kernel.org,
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From:   Jon Masters <jcm@jonmasters.org>
Organization: World Organi{s,z}ation Of Broken Dreams
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Date:   Mon, 22 Jan 2018 14:00:59 -0500
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Subject: Re: [PATCH v3 1/2] arm64: Branch predictor hardening for Cavium
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On 01/22/2018 06:33 AM, Will Deacon wrote:
> On Fri, Jan 19, 2018 at 04:22:47AM -0800, Jayachandran C wrote:
>> Use PSCI based mitigation for speculative execution attacks targeting
>> the branch predictor. We use the same mechanism as the one used for
>> Cortex-A CPUs, we expect the PSCI version call to have a side effect
>> of clearing the BTBs.
>>
>> Signed-off-by: Jayachandran C <jnair@caviumnetworks.com>
>> ---
>>  arch/arm64/kernel/cpu_errata.c | 10 ++++++++++
>>  1 file changed, 10 insertions(+)
>>
>> diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c
>> index 70e5f18..45ff9a2 100644
>> --- a/arch/arm64/kernel/cpu_errata.c
>> +++ b/arch/arm64/kernel/cpu_errata.c
>> @@ -338,6 +338,16 @@ const struct arm64_cpu_capabilities arm64_errata[] = {
>>  		.capability = ARM64_HARDEN_BP_POST_GUEST_EXIT,
>>  		MIDR_ALL_VERSIONS(MIDR_QCOM_FALKOR_V1),
>>  	},
>> +	{
>> +		.capability = ARM64_HARDEN_BRANCH_PREDICTOR,
>> +		MIDR_ALL_VERSIONS(MIDR_BRCM_VULCAN),
>> +		.enable = enable_psci_bp_hardening,
>> +	},
>> +	{
>> +		.capability = ARM64_HARDEN_BRANCH_PREDICTOR,
>> +		MIDR_ALL_VERSIONS(MIDR_CAVIUM_THUNDERX2),
>> +		.enable = enable_psci_bp_hardening,
>> +	},
>>  #endif
> 
> Thanks.
> 
> Acked-by: Will Deacon <will.deacon@arm.com>

Thanks. I have separately asked for a specification tweak to allow us to
discover whether firmware has been augmented to provide the necessary
support that we need. That applies beyond Cavium.

(for now in RHEL, we've asked the vendors to give us a temporary patch
that we can match DMI or other data later in boot and warn users on)

Jon.