From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752978AbbBRKvr (ORCPT ); Wed, 18 Feb 2015 05:51:47 -0500 Received: from smtp02.citrix.com ([66.165.176.63]:48259 "EHLO SMTP02.CITRIX.COM" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751472AbbBRKvo (ORCPT ); Wed, 18 Feb 2015 05:51:44 -0500 X-IronPort-AV: E=Sophos;i="5.09,600,1418083200"; d="scan'208";a="228068378" Message-ID: <54E46EBE.9090109@citrix.com> Date: Wed, 18 Feb 2015 10:51:42 +0000 From: David Vrabel User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Icedove/31.4.0 MIME-Version: 1.0 To: Juergen Gross , David Vrabel , , , , Subject: Re: [Xen-devel] [PATCH 02/13] xen: anchor linear p2m list in shared info structure References: <1424242326-26611-1-git-send-email-jgross@suse.com> <1424242326-26611-3-git-send-email-jgross@suse.com> <54E46A33.9030401@citrix.com> <54E46CB1.5010702@suse.com> In-Reply-To: <54E46CB1.5010702@suse.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 On 18/02/15 10:42, Juergen Gross wrote: > On 02/18/2015 11:32 AM, David Vrabel wrote: >> On 18/02/15 06:51, Juergen Gross wrote: >>> The linear p2m list should be anchored in the shared info structure >> >> I'm not really sure what you mean by "anchored". > > Bad wording? What about: > > The virtual address of the linear p2m list should be stored in the > shared info structure. This is better. >>> read by the Xen tools to be able to support 64 bit pv-domains larger >>> than 512 MB. Additionally the linear p2m list interface includes a >>> generation count which is changed prior to and after each mapping >>> change of the p2m list. Reading the generation count the Xen tools can >>> detect changes of the mappings and re-read the p2m list eventually. >> [...] >>> --- a/arch/x86/xen/p2m.c >>> +++ b/arch/x86/xen/p2m.c >>> @@ -256,6 +256,10 @@ void xen_setup_mfn_list_list(void) >>> HYPERVISOR_shared_info->arch.pfn_to_mfn_frame_list_list = >>> virt_to_mfn(p2m_top_mfn); >>> HYPERVISOR_shared_info->arch.max_pfn = xen_max_p2m_pfn; >>> + HYPERVISOR_shared_info->arch.p2m_generation = 0; >>> + HYPERVISOR_shared_info->arch.p2m_vaddr = (unsigned >>> long)xen_p2m_addr; >>> + HYPERVISOR_shared_info->arch.p2m_cr3 = >>> + xen_pfn_to_cr3(virt_to_mfn(swapper_pg_dir)); >>> } >>> >>> /* Set up p2m_top to point to the domain-builder provided p2m pages */ >>> @@ -469,8 +473,10 @@ static pte_t *alloc_p2m_pmd(unsigned long addr, >>> pte_t *pte_pg) >>> >>> ptechk = lookup_address(vaddr, &level); >>> if (ptechk == pte_pg) { >>> + HYPERVISOR_shared_info->arch.p2m_generation++; >>> set_pmd(pmdp, >>> __pmd(__pa(pte_newpg[i]) | _KERNPG_TABLE)); >>> + HYPERVISOR_shared_info->arch.p2m_generation++; >> >> Do these increments of p2m_generation need to be atomic? > > Hmm, they are done under lock. Ok, atomic isn't necessary. > I don't think the compiler is allowed to > reorder the writes to p2m_generation across set_pmd(). Ok. but I think you also need to prevent the processor reordering the writes so I think some write barriers are needed here. (The toolstack would then need the corresponding read barriers when checking the p2m_generation.) David