linux-kernel - Re: [PATCH RFC] x86/bus_lock: Enable bus lock detection

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Message-ID: <20200729232808.GP27751@linux.intel.com>
Date:   Wed, 29 Jul 2020 16:28:08 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Fenghua Yu <fenghua.yu@...el.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>, Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        "Shanbhogue, Vedvyas" <vedvyas.shanbhogue@...el.com>,
        "Luck, Tony" <tony.luck@...el.com>, H Peter Anvin <hpa@...or.com>,
        Andy Lutomirski <luto@...nel.org>,
        "Shankar, Ravi V" <ravi.v.shankar@...el.com>,
        "Li, Xiaoyao" <xiaoyao.li@...el.com>, x86 <x86@...nel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RFC] x86/bus_lock: Enable bus lock detection

On Wed, Jul 29, 2020 at 10:07:14PM +0000, Fenghua Yu wrote:
> Hi, Sean,
> 
> On Wed, Jul 29, 2020 at 01:39:05PM -0700, Sean Christopherson wrote:
> > On Wed, Jul 29, 2020 at 08:35:57PM +0000, Fenghua Yu wrote:
> > > If sld=fatal and bld=ratelimit (both sld and bld are enabled in hw),
> > > a split lock always generates #AC and kills the app and bld will never have
> > > a chance to trigger #DB for split lock. So effectively the combination makes
> > > the kernel to take two different actions after detecting a bus lock: if the
> > > bus lock comes from a split lock, fatal (sld); if the bus lock comes from
> > > lock to non-WB memory, ratelimit (bld). Seems this is not a useful combination
> > > and is not what the user really wants to do because the user wants ratelimit
> > > for BLD, right?
> > 
> > I understood all off that.  And as I user I want to run sld=fatal and
> > bld=ratelimit to provide maximum protection, i.e. disallow split locks at
> > all times, and ratelimit the crud SLD #AC can't catch.
> 
> Then this will expand the current usages and do need two options. Let me work
> on adding a new "bus_lock_detect=" option as you suggested.

I'd wait for feedback from others before spending too much effort rewriting
everything, I'm just one person with an opinion.