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

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Date:   Wed, 21 Apr 2021 13:36:03 -0500
From:   "Saripalli, RK" <rsaripal@....com>
To:     Bandan Das <bsd@...hat.com>, Randy Dunlap <rdunlap@...radead.org>
Cc:     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

Bandan / Randy, this convention was chosen based on review of the earlier patches from Boris.

For now, the functionality will be just on and off.
Later based on interest from community and other factors, I will online the prctl and seccomp variants of the 
mitigation.

Thanks,
RK

On 4/21/2021 1:32 PM, Bandan Das wrote:
> 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.
>