From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx104.postini.com [74.125.245.104]) by kanga.kvack.org (Postfix) with SMTP id 7F3656B0069 for ; Tue, 15 Jan 2013 13:38:18 -0500 (EST) Message-ID: <50F5A215.5020708@redhat.com> Date: Tue, 15 Jan 2013 13:38:13 -0500 From: Rik van Riel MIME-Version: 1.0 Subject: Re: [RFCv3][PATCH 2/3] fix kvm's use of __pa() on percpu areas References: <20130109185904.DD641DCE@kernel.stglabs.ibm.com> <20130109185905.0DCFC236@kernel.stglabs.ibm.com> In-Reply-To: <20130109185905.0DCFC236@kernel.stglabs.ibm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Dave Hansen Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Gleb Natapov , Ingo Molnar , "H. Peter Anvin" , x86@kernel.org, Marcelo Tosatti On 01/09/2013 01:59 PM, Dave Hansen wrote: > In short, it is illegal to call __pa() on an address holding > a percpu variable. The times when this actually matters are > pretty obscure (certain 32-bit NUMA systems), but it _does_ > happen. It is important to keep KVM guests working on these > systems because the real hardware is getting harder and > harder to find. > > This bug manifested first by me seeing a plain hang at boot > after this message: > > CPU 0 irqstacks, hard=f3018000 soft=f301a000 > > or, sometimes, it would actually make it out to the console: > > [ 0.000000] BUG: unable to handle kernel paging request at ffffffff > > I eventually traced it down to the KVM async pagefault code. > This can be worked around by disabling that code either at > compile-time, or on the kernel command-line. Acked-by: Rik van Riel -- All rights reversed -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org