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Subject: Re: [PATCH 0/3] arm64: cpufeature: Add filter function to control
To:     Marc Zyngier <maz@kernel.org>
Cc:     catalin.marinas@arm.com, will@kernel.org, pajay@qti.qualcomm.com,
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References: <1610152163-16554-1-git-send-email-sramana@codeaurora.org>
 <6dfdf691b5ed57df81c4c61422949af5@misterjones.org>
From:   Srinivas Ramana <sramana@codeaurora.org>
Message-ID: <c028d65d-27c3-826a-b16c-407e9cf48aac@codeaurora.org>
Date:   Wed, 13 Jan 2021 23:15:47 -0800
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Hi Marc,

On 1/11/2021 5:40 AM, Marc Zyngier wrote:
> Hi Srinivas,
>
> On 2021-01-09 00:29, Srinivas Ramana wrote:
>> This patchset adds a control function for cpufeature framework
>> so that the feature can be controlled at runtime.
>>
>> Defer PAC on boot core and use the filter function added to disable
>> PAC from command line. This will help toggling the feature on systems
>> that do not support PAC or where PAC needs to be disabled at runtime,
>> without modifying the core kernel.
>>
>> The idea of adding the filter function for cpufeature is taken from
>> https://lore.kernel.org/linux-arm-kernel/20200515171612.1020-25-catalin.marinas@arm.com/ 
>>
>> https://lore.kernel.org/linux-arm-kernel/20200515171612.1020-24-catalin.marinas@arm.com/ 
>>
>>
>> Srinivas Ramana (3):
>>   arm64: Defer enabling pointer authentication on boot core
>>   arm64: cpufeature: Add a filter function to cpufeature
>>   arm64: Enable control of pointer authentication using early param
>>
>>  Documentation/admin-guide/kernel-parameters.txt |  6 +++
>>  arch/arm64/include/asm/cpufeature.h             |  8 +++-
>>  arch/arm64/include/asm/pointer_auth.h           | 10 +++++
>>  arch/arm64/include/asm/stackprotector.h         |  1 +
>>  arch/arm64/kernel/cpufeature.c                  | 53 
>> +++++++++++++++++++------
>>  arch/arm64/kernel/head.S                        |  4 --
>>  6 files changed, 64 insertions(+), 18 deletions(-)
>
> I've been working for some time on a similar series to allow a feature
> set to be disabled during the early boot phase, initially to prevent
> booting a kernel with VHE, but the mechanism is generic enough to
> deal with most architectural features.
>
> I took the liberty to lift your first patch and to add it to my 
> series[1],
> further allowing PAuth to be disabled at boot time on top of BTI and VHE.
>
> I'd appreciate your comments on this.
Thanks for sending this series. It seems to be more flexible compared 
you what we did.
Following your discussion on allowing EXACT ftr_reg values.


Btw, do you have plan to add MTE in similar lines to control the feature?
We may be needing this on some systems.
>
> Thanks,
>
>         M.
>
> [1] https://lore.kernel.org/r/20210111132811.2455113-1-maz@kernel.org


Thanks,

-- Srinivas R