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Subject: Re: [PATCH v4 19/21] arm64: cpufeatures: Allow disabling of BTI from
 the command-line
To:     Catalin Marinas <catalin.marinas@arm.com>,
        Marc Zyngier <maz@kernel.org>
Cc:     linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu,
        linux-kernel@vger.kernel.org, Will Deacon <will@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        David Brazdil <dbrazdil@google.com>,
        Alexandru Elisei <alexandru.elisei@arm.com>,
        Ard Biesheuvel <ardb@kernel.org>,
        Jing Zhang <jingzhangos@google.com>,
        Ajay Patil <pajay@qti.qualcomm.com>,
        Prasad Sodagudi <psodagud@codeaurora.org>,
        James Morse <james.morse@arm.com>,
        Julien Thierry <julien.thierry.kdev@gmail.com>,
        Suzuki K Poulose <suzuki.poulose@arm.com>,
        kernel-team@android.com
References: <20210118094533.2874082-1-maz@kernel.org>
 <20210118094533.2874082-20-maz@kernel.org>
 <YAwxhuw8L0Fp3cUf@Catalins-MacBook-Air.local>
From:   Srinivas Ramana <sramana@codeaurora.org>
Message-ID: <f78c9df6-1dc1-a2fa-08c9-5b9e890c320e@codeaurora.org>
Date:   Tue, 26 Jan 2021 12:35:05 -0800
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Hi Marc,

On 1/23/2021 6:24 AM, Catalin Marinas wrote:
> On Mon, Jan 18, 2021 at 09:45:31AM +0000, Marc Zyngier wrote:
>> In order to be able to disable BTI at runtime, whether it is
>> for testing purposes, or to work around HW issues, let's add
>> support for overriding the ID_AA64PFR1_EL1.BTI field.
>>
>> This is further mapped on the arm64.nobti command-line alias.
>>
>> Signed-off-by: Marc Zyngier <maz@kernel.org>
> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Verified this Series for BTI as well for command line control.
With arm64.nobti:
BTI is disabled on both primary and secondary cores as expected(verified 
page table entries).
HWCAPs show no BTI support and kernel instructions are being treated as 
NOPs.
We don't have plan to repeat the test on v5 as there are not major 
changes here.

Tested-by: Srinivas Ramana <sramana@codeaurora.org>