From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752810AbbJBOdj (ORCPT ); Fri, 2 Oct 2015 10:33:39 -0400 Received: from smtp02.citrix.com ([66.165.176.63]:2925 "EHLO SMTP02.CITRIX.COM" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752040AbbJBOdi (ORCPT ); Fri, 2 Oct 2015 10:33:38 -0400 X-IronPort-AV: E=Sophos;i="5.17,623,1437436800"; d="scan'208";a="307686210" Message-ID: <560E9551.6020105@citrix.com> Date: Fri, 2 Oct 2015 15:31:45 +0100 From: Julien Grall User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Icedove/31.8.0 MIME-Version: 1.0 To: David Vrabel , CC: Wei Liu , , "Konrad Rzeszutek Wilk" , , , Boris Ostrovsky , Subject: Re: [PATCH v5 12/22] xen/balloon: Don't rely on the page granularity is the same for Xen and Linux References: <1443609937-25278-1-git-send-email-julien.grall@citrix.com> <1443609937-25278-13-git-send-email-julien.grall@citrix.com> <560E9004.8030604@citrix.com> In-Reply-To: <560E9004.8030604@citrix.com> Content-Type: text/plain; charset="windows-1252" Content-Transfer-Encoding: 7bit X-DLP: MIA2 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi David, On 02/10/15 15:09, David Vrabel wrote: > On 30/09/15 11:45, Julien Grall wrote: >> For ARM64 guests, Linux is able to support either 64K or 4K page >> granularity. Although, the hypercall interface is always based on 4K >> page granularity. >> >> With 64K page granularity, a single page will be spread over multiple >> Xen frame. >> >> To avoid splitting the page into 4K frame, take advantage of the >> extent_order field to directly allocate/free chunk of the Linux page >> size. >> >> Note that PVMMU is only used for PV guest (which is x86) and the page >> granularity is always 4KB. Some BUILD_BUG_ON has been added to ensure >> that because the code has not been modified. > > This causes a BUG() in x86 PV guests when decreasing the reservation. > > Xen says: > > (XEN) d0v2 Error pfn 0: rd=0 od=32753 caf=8000000000000001 > taf=7400000000000001 > (XEN) memory.c:250:d0v2 Bad page free for domain 0 > > And Linux BUGs with: > > [ 82.032654] kernel BUG at > /anfs/drall/scratch/davidvr/x86/linux/drivers/xen/balloon.c:540! > > Which is a non-zero return value from the decrease_reservation hypercall. > > The frame_list[] has been incorrectly populated. The below patch fixes > it for me. Please test as well. Sorry for the breakage, I think I haven't spot the bug on my board because most the PV drivers are allocating one balloon page at the time by default. This patch looks valid to me. i was resetting and incremented for each loop on an early version. Although I dropped it by mistake when I use a different way to decrease the reservation. Regards, -- Julien Grall