linux-kernel - Re: [PATCH 4/4] x86/speculation: Add PSF mitigation kernel parameters

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Date:   Wed, 21 Apr 2021 14:32:13 -0400
From:   Bandan Das <bsd@...hat.com>
To:     Randy Dunlap <rdunlap@...radead.org>
Cc:     Ramakrishna Saripalli <rsaripal@....com>,
        linux-kernel@...r.kernel.org, x86@...nel.org, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, Jonathan Corbet <corbet@....net>
Subject: Re: [PATCH 4/4] x86/speculation: Add PSF mitigation kernel parameters

Randy Dunlap <rdunlap@...radead.org> writes:

> Hi,
>
> On 4/21/21 2:01 AM, Ramakrishna Saripalli wrote:
>> From: Ramakrishna Saripalli <rk.saripalli@....com>
>> 
>> PSF mitigation introduces a new kernel parameter called
>> 	predict_store_fwd.
>> 
>> Signed-off-by: Ramakrishna Saripalli<rk.saripalli@....com>
>> ---
>>  Documentation/admin-guide/kernel-parameters.txt | 5 +++++
>>  1 file changed, 5 insertions(+)
>> 
>> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
>> index 04545725f187..58f6bd02385b 100644
>> --- a/Documentation/admin-guide/kernel-parameters.txt
>> +++ b/Documentation/admin-guide/kernel-parameters.txt
>> @@ -3940,6 +3940,11 @@
>>  			Format: {"off"}
>>  			Disable Hardware Transactional Memory
>>  
>> +	predict_store_fwd	[X86] This option controls PSF mitigation
>> +			off - Turns on PSF mitigation.
>> +			on  - Turns off PSF mitigation.
>> +			default : on.
>
> This should be formatted more like:
>
> +	predict_store_fwd=	[X86] This option controls PSF mitigation
> +			off - Turns on PSF mitigation.
> +			on  - Turns off PSF mitigation.
> +			default: on.
>
> But why does "off" turn it on and "on" turn it off?
>
Maybe, rename the parameter to something like psfd_disable, then off -> disables mitigation and on -> enables it.
Or just rewriting this to off -> turns off predictive store forwarding is probably ok too.

Bandan

>
>> +
>>  	preempt=	[KNL]
>>  			Select preemption mode if you have CONFIG_PREEMPT_DYNAMIC
>>  			none - Limited to cond_resched() calls
>> 
>
> thanks.