Re: [lkp-robot] [x86] 69218e4799: BUG:kernel_hang_in_boot_stage

From: Thomas Garnier <thgarnie@google.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: "kernel test robot" <xiaolong.ye@intel.com>,
	"Ingo Molnar" <mingo@kernel.org>,
	"Alexander Potapenko" <glider@google.com>,
	"Andrew Morton" <akpm@linux-foundation.org>,
	"Andrey Ryabinin" <aryabinin@virtuozzo.com>,
	"Andy Lutomirski" <luto@kernel.org>,
	"Ard Biesheuvel" <ard.biesheuvel@linaro.org>,
	"Boris Ostrovsky" <boris.ostrovsky@oracle.com>,
	"Borislav Petkov" <bp@suse.de>,
	"Chris Wilson" <chris@chris-wilson.co.uk>,
	"Christian Borntraeger" <borntraeger@de.ibm.com>,
	"Dmitry Vyukov" <dvyukov@google.com>,
	"Frederic Weisbecker" <fweisbec@gmail.com>,
	"Jiri Kosina" <jikos@kernel.org>,
	"Joerg Roedel" <joro@8bytes.org>,
	"Jonathan Corbet" <corbet@lwn.net>,
	"Josh Poimboeuf" <jpoimboe@redhat.com>,
	"Juergen Gross" <jgross@suse.com>,
	"Kees Cook" <keescook@chromium.org>,
	"Len Brown" <len.brown@intel.com>,
	"Lorenzo Stoakes" <lstoakes@gmail.com>,
	"Luis R . Rodriguez" <mcgrof@kernel.org>,
	"Matt Fleming" <matt@codeblueprint.co.uk>,
	"Michal Hocko" <mhocko@suse.com>,
	"Paolo Bonzini" <pbonzini@redhat.com>,
	"Paul Gortmaker" <paul.gortmaker@windriver.com>,
	"Pavel Machek" <pavel@ucw.cz>,
	"Peter Zijlstra" <peterz@infradead.org>,
	"Radim Krčmář" <rkrcmar@redhat.com>,
	"Rafael J . Wysocki" <rjw@rjwysocki.net>,
	"Rusty Russell" <rusty@rustcorp.com.au>,
	"Stanislaw Gruszka" <sgruszka@redhat.com>,
	"Thomas Gleixner" <tglx@linutronix.de>,
	"Tim Chen" <tim.c.chen@linux.intel.com>,
	"Vitaly Kuznetsov" <vkuznets@redhat.com>,
	zijun_hu <zijun_hu@htc.com>, LKML <linux-kernel@vger.kernel.org>,
	"Stephen Rothwell" <sfr@canb.auug.org.au>, LKP <lkp@01.org>
Subject: Re: [lkp-robot] [x86] 69218e4799: BUG:kernel_hang_in_boot_stage
Date: Tue, 21 Mar 2017 13:25:24 -0700	[thread overview]
Message-ID: <CAJcbSZFuJiJE0=rS-ZGPLCMUgaz+dPzHUm-iMa=J1E4H0qAHFg@mail.gmail.com> (raw)
In-Reply-To: <CAJcbSZHFYz4wpBftvS40Gv9X5Epuk43wLStv9-7axWd3965fcw@mail.gmail.com>

The issue seems to be related to exceptions happening in close pages
to the fixmap GDT remapping.

The original page fault happen in do_test_wp_bit which set a fixmap
entry to test WP flag. If I grow the number of processors supported
increasing the distance between the remapped GDT page and the WP test
page, the error does not reproduce.

I am still looking at the exact distance between repro and no-repro as
well as the exact root cause.

On Tue, Mar 21, 2017 at 12:23 PM, Thomas Garnier <thgarnie@google.com> wrote:
> On Tue, Mar 21, 2017 at 12:20 PM, Linus Torvalds
> <torvalds@linux-foundation.org> wrote:
>>
>> On Tue, Mar 21, 2017 at 11:16 AM, Thomas Garnier <thgarnie@google.com> wrote:
>> > This error happens even with Andy TLS fix on 32-bit (GDT is on fixmap
>> > but not readonly). I am looking into it.
>> >
>> > KVM internal error. Suberror: 3
>> > extra data[0]: 80000b0e
>> > extra data[1]: 31
>>
>> If I read that right, it's extra data[1] 0x31, which EXIT_REASON_EPT_MISCONFIG.
>>
>> I'm not seeing how the A bit in a GDT entry could have anything to do
>> with it. I'm assuming it happens even without Andy's patch?
>
> Correct.
>
>>
>>                   Linus
>
>
>
>
> --
> Thomas

-- 
Thomas