linux-kernel - Re: [PATCH v3] x86/speculation/l1tf: Add KConfig for setting the L1D cache flush mode

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Date:   Thu, 2 Jul 2020 23:43:47 -0700
From:   Abhishek Bhardwaj <abhishekbh@...gle.com>
To:     Anthony Steinhauser <asteinhauser@...gle.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Waiman Long <longman@...hat.com>,
        Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Mark Gross <mgross@...ux.intel.com>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Tony Luck <tony.luck@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>, kvm@...r.kernel.org,
        x86 <x86@...nel.org>, Doug Anderson <dianders@...gle.com>
Subject: Re: [PATCH v3] x86/speculation/l1tf: Add KConfig for setting the L1D
 cache flush mode

We have tried to steer away from kernel command line args for a few reasons.

I am paraphrasing my colleague Doug's argument here (CC'ed him as well) -

- The command line args are getting unwieldy. Kernel command line
parameters are not a scalable way to set kernel config. It's intended
as a super limited way for the bootloader to pass info to the kernel
and also as a way for end users who are not compiling the kernel
themselves to tweak kernel behavior.

- Also, we know we want this setting from the start. This is a
definite smell that it deserves to be a compile time thing rather than
adding extra code + whatever miniscule time at runtime to pass an
extra arg.

I think this was what CONFIGS were intended for. I'm happy to add all
this to the commit message once it's approved in spirit by the
maintainers.

On Thu, Jul 2, 2020 at 8:18 PM Anthony Steinhauser
<asteinhauser@...gle.com> wrote:
>
> Yes, this probably requires an explanation why the change is necessary
> or useful. Without that it is difficult to give some meaningful
> feedback.



-- 
Abhishek