linux-kernel - Re: __schedule #DF splat

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Message-ID: <20140629140104.GB12528@pd.tnic>
Date:	Sun, 29 Jun 2014 16:01:04 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Gleb Natapov <gleb@...nel.org>
Cc:	Jan Kiszka <jan.kiszka@....de>,
	Paolo Bonzini <pbonzini@...hat.com>,
	lkml <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>, x86-ml <x86@...nel.org>,
	kvm@...r.kernel.org, Jörg Rödel <joro@...tes.org>
Subject: Re: __schedule #DF splat

On Sun, Jun 29, 2014 at 04:42:47PM +0300, Gleb Natapov wrote:
> Please do so and let us know.

Yep, just did. Reverting ae9fedc793 fixes the issue.

> reinj:1 means that previous injection failed due to another #PF that
> happened during the event injection itself This may happen if GDT or fist
> instruction of a fault handler is not mapped by shadow pages, but here
> it says that the new page fault is at the same address as the previous
> one as if GDT is or #PF handler is mapped there. Strange. Especially
> since #DF is injected successfully, so GDT should be fine. May be wrong
> cpl makes svm crazy?

Well, I'm not going to even pretend to know kvm to know *when* we're
saving VMCB state but if we're saving the wrong CPL and then doing the
pagetable walk, I can very well imagine if the walker gets confused. One
possible issue could be U/S bit (bit 2) in the PTE bits which allows
access to supervisor pages only when CPL < 3. I.e., CPL has effect on
pagetable walk and a wrong CPL level could break it.

All a conjecture though...

-- 
Regards/Gruss,
    Boris.

Sent from a fat crate under my desk. Formatting is fine.
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