linux-kernel - Re: [PATCH v10 6/6] x86/split_lock: Enable split lock detection by kernel parameter

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Message-ID: <CALCETrUBomb2_2xyX-tZUD84smtDWH6e16zSN1qupkv-DWu5kw@mail.gmail.com>
Date:   Fri, 22 Nov 2019 13:25:45 -0800
From:   Andy Lutomirski <luto@...nel.org>
To:     Fenghua Yu <fenghua.yu@...el.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        "Luck, Tony" <tony.luck@...el.com>, Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        H Peter Anvin <hpa@...or.com>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "Shankar, Ravi V" <ravi.v.shankar@...el.com>,
        linux-kernel <linux-kernel@...r.kernel.org>, x86 <x86@...nel.org>
Subject: Re: [PATCH v10 6/6] x86/split_lock: Enable split lock detection by
 kernel parameter

On Fri, Nov 22, 2019 at 12:29 PM Fenghua Yu <fenghua.yu@...el.com> wrote:
>
> On Fri, Nov 22, 2019 at 09:23:45PM +0100, Peter Zijlstra wrote:
> > On Fri, Nov 22, 2019 at 06:02:04PM +0000, Luck, Tony wrote:
> > > > it requires we get the kernel and firmware clean, but only warns about
> > > > dodgy userspace, which I really don't think there is much of.
> > > >
> > > > getting the kernel clean should be pretty simple.
> > >
> > > Fenghua has a half dozen additional patches (I think they were
> > > all posted in previous iterations of the patch) that were found by
> > > code inspection, rather than by actually hitting them.
> >
> > I thought we merged at least some of that, but maybe my recollection is
> > faulty.
>
> At least 2 key fixes are in TIP tree:
> https://lore.kernel.org/lkml/157384597983.12247.8995835529288193538.tip-bot2@tip-bot2/
> https://lore.kernel.org/lkml/157384597947.12247.7200239597382357556.tip-bot2@tip-bot2/

I do not like these patches at all.  I would *much* rather see the
bitops fixed and those patches reverted.

Is there any Linux architecture that doesn't have 32-bit atomic
operations?  If all architectures can support them, then we should add
set_bit_u32(), etc and/or make x86's set_bit() work for a
4-byte-aligned pointer.

--Andy