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From: Gleb Natapov <gleb@kernel.org>
To: Borislav Petkov <bp@alien8.de>
Cc: "Paolo Bonzini" <pbonzini@redhat.com>,
	lkml <linux-kernel@vger.kernel.org>,
	"Peter Zijlstra" <peterz@infradead.org>,
	"Steven Rostedt" <rostedt@goodmis.org>, x86-ml <x86@kernel.org>,
	kvm@vger.kernel.org, "Jörg Rödel" <joro@8bytes.org>
Subject: Re: __schedule #DF splat
Date: Sun, 29 Jun 2014 09:46:27 +0300	[thread overview]
Message-ID: <20140629064626.GD18167@minantech.com> (raw)
In-Reply-To: <20140628114431.GB4373@pd.tnic>

On Sat, Jun 28, 2014 at 01:44:31PM +0200, Borislav Petkov wrote:
>  qemu-system-x86-20240 [006] ...1  9406.484134: kvm_page_fault: address 7fffb62ba318 error_code 2
>  qemu-system-x86-20240 [006] ...1  9406.484136: kvm_inj_exception: #PF (0x2)a
> 
> kvm injects the #PF into the guest.
> 
>  qemu-system-x86-20240 [006] d..2  9406.484136: kvm_entry: vcpu 1
>  qemu-system-x86-20240 [006] d..2  9406.484137: kvm_exit: reason PF excp rip 0xffffffff8161130f info 2 7fffb62ba318
>  qemu-system-x86-20240 [006] ...1  9406.484138: kvm_page_fault: address 7fffb62ba318 error_code 2
>  qemu-system-x86-20240 [006] ...1  9406.484141: kvm_inj_exception: #DF (0x0)
> 
> Second #PF at the same address and kvm injects the #DF.
> 
> BUT(!), why?
> 
> I probably am missing something but WTH are we pagefaulting at a
> user address in context_switch() while doing a lockdep call, i.e.
> spin_release? We're not touching any userspace gunk there AFAICT.
> 
> Is this an async pagefault or so which kvm is doing so that the guest
> rip is actually pointing at the wrong place?
> 
There is nothing in the trace that point to async pagefault as far as I see.

> Or something else I'm missing, most probably...
> 
Strange indeed. Can you also enable kvmmmu tracing? You can also instrument
kvm_multiple_exception() to see which two exception are combined into #DF.

--
			Gleb.

  reply	other threads:[~2014-06-29  6:46 UTC|newest]

Thread overview: 30+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-06-25 15:32 __schedule #DF splat Borislav Petkov
2014-06-25 20:26 ` Borislav Petkov
2014-06-27 10:18   ` Borislav Petkov
2014-06-27 11:41     ` Paolo Bonzini
2014-06-27 11:55       ` Borislav Petkov
2014-06-27 12:01         ` Paolo Bonzini
2014-06-27 12:10           ` Borislav Petkov
2014-06-28 11:44             ` Borislav Petkov
2014-06-29  6:46               ` Gleb Natapov [this message]
2014-06-29  9:56                 ` Jan Kiszka
2014-06-29 10:24                   ` Gleb Natapov
2014-06-29 10:31                     ` Jan Kiszka
2014-06-29 10:53                       ` Gleb Natapov
2014-06-29 10:59                         ` Jan Kiszka
2014-06-29 11:51                           ` Borislav Petkov
2014-06-29 12:22                             ` Jan Kiszka
2014-06-29 13:14                               ` Borislav Petkov
2014-06-29 13:42                                 ` Gleb Natapov
2014-06-29 14:01                                   ` Borislav Petkov
2014-06-29 14:27                                     ` Gleb Natapov
2014-06-29 14:32                                       ` Jan Kiszka
2014-06-29 14:51                                         ` Jan Kiszka
2014-06-29 15:12                                           ` [PATCH] KVM: SVM: Fix CPL export via SS.DPL Jan Kiszka
2014-06-29 18:00                                             ` Borislav Petkov
2014-06-30 15:01                                             ` Paolo Bonzini
2014-06-30 15:03                                               ` Jan Kiszka
2014-06-30 15:15                                                 ` Borislav Petkov
2014-06-30 15:25                                                   ` Gleb Natapov
2014-06-30 15:26                                                 ` Paolo Bonzini
2014-06-29 13:46                                 ` __schedule #DF splat Borislav Petkov

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