From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752700AbbJBOJW (ORCPT ); Fri, 2 Oct 2015 10:09:22 -0400 Received: from smtp02.citrix.com ([66.165.176.63]:64367 "EHLO SMTP02.CITRIX.COM" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751841AbbJBOJV (ORCPT ); Fri, 2 Oct 2015 10:09:21 -0400 X-IronPort-AV: E=Sophos;i="5.17,623,1437436800"; d="scan'208";a="307679671" Message-ID: <560E9004.8030604@citrix.com> Date: Fri, 2 Oct 2015 15:09:08 +0100 From: David Vrabel User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Icedove/31.8.0 MIME-Version: 1.0 To: Julien Grall , CC: , , , , "Konrad Rzeszutek Wilk" , Boris Ostrovsky , Wei Liu 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> In-Reply-To: <1443609937-25278-13-git-send-email-julien.grall@citrix.com> Content-Type: text/plain; charset="windows-1252" Content-Transfer-Encoding: 7bit X-DLP: MIA1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. --- a/drivers/xen/balloon.c +++ b/drivers/xen/balloon.c @@ -504,9 +504,10 @@ static enum bp_state decrease_reservation(unsigned long nr_pages, gfp_t gfp) * Setup the frame, update direct mapping, invalidate P2M, * and add to balloon. */ + i = 0; list_for_each_entry_safe(page, tmp, &pages, lru) { /* XENMEM_decrease_reservation requires a GFN */ - frame_list[i] = xen_page_to_gfn(page); + frame_list[i++] = xen_page_to_gfn(page); #ifdef CONFIG_XEN_HAVE_PVMMU /* David