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Date:   Tue, 23 Jan 2018 09:51:01 +0000
From:   Will Deacon <will.deacon@arm.com>
To:     Jon Masters <jcm@jonmasters.org>
Cc:     Jayachandran C <jnair@caviumnetworks.com>, marc.zyngier@arm.com,
        linux-arm-kernel@lists.infradead.org, lorenzo.pieralisi@arm.com,
        ard.biesheuvel@linaro.org, catalin.marinas@arm.com,
        linux-kernel@vger.kernel.org, labbott@redhat.com,
        christoffer.dall@linaro.org
Subject: Re: [PATCH v3 1/2] arm64: Branch predictor hardening for Cavium
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On Mon, Jan 22, 2018 at 02:00:59PM -0500, Jon Masters wrote:
> 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.

AFAIK, there's already an SMCCC/PSCI proposal doing the rounds that is
discoverable and does what we need. Have you seen it? We should be posting
code this week.

Will