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From:   Thomas Gleixner <tglx@linutronix.de>
To:     "Singh\, Balbir" <sblbir@amazon.com>,
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Subject: Re:  [PATCH v6 5/6] Optionally flush L1D on context switch
In-Reply-To: <c51109f10f6572f5cf60d2693f84ff8e65c7804a.camel@amazon.com>
References: <20200510014803.12190-1-sblbir@amazon.com> <20200510014803.12190-6-sblbir@amazon.com> <875zcz3j47.fsf@nanos.tec.linutronix.de> <c51109f10f6572f5cf60d2693f84ff8e65c7804a.camel@amazon.com>
Date:   Thu, 14 May 2020 13:33:02 +0200
Message-ID: <87pnb6zr81.fsf@nanos.tec.linutronix.de>
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Balbir,

"Singh, Balbir" <sblbir@amazon.com> writes:
> On Wed, 2020-05-13 at 18:16 +0200, Thomas Gleixner wrote:
>> Balbir Singh <sblbir@amazon.com> writes:
>> But looking at this deeper (yes I should have noticed earlier):
>> 
>>     Why do we need yet another PRCTL?
>> 
>> We already have PR_SET_SPECULATION_CTRL/PR_GET_SPECULATION_CTRL. That
>> L1D flush thingy fits into this category, right?
>
> It does, I thought about it for a while when I was changing the code and
> left it aside because, looking at the definition
>
> 1    PR_SPEC_ENABLE         The speculation feature is enabled,
> mitigation is disabled.
> 2    PR_SPEC_DISABLE        The speculation feature is disabled,
> mitigation is enabled.
>
> With L1D flush, there is no overriding of the feature as such (as in
> enable when the mitigation is disabled and vice-versa). I am happy to
> reconsider my initial thought though.

L1D is always enabled as L1D will be a source of trouble forever :)

Thanks,

        tglx