From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754977Ab3HAMEt (ORCPT ); Thu, 1 Aug 2013 08:04:49 -0400 Received: from smtp.citrix.com ([66.165.176.89]:57457 "EHLO SMTP.CITRIX.COM" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754862Ab3HAMEr (ORCPT ); Thu, 1 Aug 2013 08:04:47 -0400 X-IronPort-AV: E=Sophos;i="4.89,793,1367971200"; d="scan'208";a="40727496" Message-ID: <51FA4EDD.4040509@citrix.com> Date: Thu, 1 Aug 2013 13:04:45 +0100 From: David Vrabel User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.16) Gecko/20121215 Iceowl/1.0b1 Icedove/3.0.11 MIME-Version: 1.0 To: Andres Lagar-Cavilla CC: "linux-kernel@vger.kernel.org" , "xen-devel@lists.xen.org" , Konrad Rzeszutek Wilk , Andres Lagar-Cavilla , Subject: Re: [PATCH] Xen: Fix retry calls into PRIVCMD_MMAPBATCH*. References: <1375203632-23854-1-git-send-email-andres@lagarcavilla.org> <2BE2F119-7375-4C8D-933D-9BCD5A9B7552@gridcentric.ca> <51FA4547.7080408@citrix.com> <5373EBB3-5CF1-4A2F-B821-1DD788877F75@gridcentric.ca> In-Reply-To: <5373EBB3-5CF1-4A2F-B821-1DD788877F75@gridcentric.ca> Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.80.2.76] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 01/08/13 12:49, Andres Lagar-Cavilla wrote: > On Aug 1, 2013, at 7:23 AM, David Vrabel wrote: > >> On 01/08/13 04:30, Andres Lagar-Cavilla wrote: >>> -- Resend as I haven't seen this hit the lists. Maybe some smtp misconfig. Apologies. Also expanded cc -- >>> >>> When a foreign mapper attempts to map guest frames that are paged out, >>> the mapper receives an ENOENT response and will have to try again >>> while a helper process pages the target frame back in. >>> >>> Gating checks on PRIVCMD_MMAPBATCH* ioctl args were preventing retries >>> of mapping calls. >> >> This breaks the auto_translated_physmap case as will allocate another >> set of empty pages and leak the previous set. > > David, > not able to follow you here. Under what circumstances will another > set of empty pages be allocated? And where? are we talking page table pages? .... vma = find_vma(mm, m.addr); if (!vma || vma->vm_ops != &privcmd_vm_ops || (m.addr != vma->vm_start) || ((m.addr + (nr_pages << PAGE_SHIFT)) != vma->vm_end) || !privcmd_enforce_singleshot_mapping(vma)) { up_write(&mm->mmap_sem); ret = -EINVAL; goto out; } if (xen_feature(XENFEAT_auto_translated_physmap)) { ret = alloc_empty_pages(vma, m.num); Here. if (ret < 0) { up_write(&mm->mmap_sem); goto out; } } >> This privcmd_enforce_singleshot_mapping() stuff seems very odd anyway. >> Does anyone know what it was for originally? It would be preferrable if >> we could update the mappings with a new set of foreign MFNs without >> having to tear down the VMA and recreate a new VMA. > > I believe it's mostly historical. I agree with you on principle, but recreating VMAs is super-cheap. Tearing them down is not cheap as each page requires a trap-and-emulate to clear the PTE (see ptep_get_and_clear_full() in zap_pte_range()). David