linux-kernel - Re: WARNING in memtype

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Message-ID: <87wo5l4ecm.fsf@nanos.tec.linutronix.de>
Date:   Sat, 09 May 2020 12:00:57 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Greg KH <gregkh@...uxfoundation.org>,
        syzbot <syzbot+353be47c9ce21b68b7ed@...kaller.appspotmail.com>,
        bp@...en8.de, dave.hansen@...ux.intel.com,
        dmitry.torokhov@...il.com, ebiederm@...ssion.com, hpa@...or.com,
        jeremy.linton@....com, linux-kernel@...r.kernel.org,
        linux-usb@...r.kernel.org, luto@...nel.org, mingo@...hat.com,
        peterz@...radead.org, stern@...land.harvard.edu,
        syzkaller-bugs@...glegroups.com, x86@...nel.org
Subject: Re: WARNING in memtype_reserve

Greg KH <gregkh@...uxfoundation.org> writes:
> On Sat, May 09, 2020 at 12:20:14AM -0700, syzbot wrote:
>> memtype_reserve failed: [mem 0xffffffffff000-0x00008fff], req write-back
>> WARNING: CPU: 1 PID: 7025 at arch/x86/mm/pat/memtype.c:589 memtype_reserve+0x69f/0x820 arch/x86/mm/pat/memtype.c:589
>
> So should memtype_reserve() not do a WARN if given invalid parameters as
> it can be triggered by userspace requests?
>
> A normal "invalid request" debug line is probably all that is needed,
> right?

I disagree. The callsite espcially if user space triggerable should not
attempt to ask for a reservation where start > end:

  >> memtype_reserve failed: [mem 0xffffffffff000-0x00008fff], req write-back

The real question is which part of the call chain is responsible for
this. That needs to be fixed.

Thanks,

        tglx