From patchwork Wed Jun 22 11:19:26 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: David Vrabel X-Patchwork-Id: 9192455 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id 029A5601C0 for ; Wed, 22 Jun 2016 11:20:51 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id E620F1FEDE for ; Wed, 22 Jun 2016 11:20:50 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id DAF60283F7; Wed, 22 Jun 2016 11:20:50 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-4.2 required=2.0 tests=BAYES_00, RCVD_IN_DNSWL_MED autolearn=ham version=3.3.1 Received: from lists.xenproject.org (lists.xenproject.org [192.237.175.120]) (using TLSv1.2 with cipher AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.wl.linuxfoundation.org (Postfix) with ESMTPS id 767E11FEDE for ; Wed, 22 Jun 2016 11:20:49 +0000 (UTC) Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.84_2) (envelope-from ) id 1bFgBy-0004Jl-Ar; Wed, 22 Jun 2016 11:19:34 +0000 Received: from mail6.bemta3.messagelabs.com ([195.245.230.39]) by lists.xenproject.org with esmtp (Exim 4.84_2) (envelope-from ) id 1bFgBw-0004JE-AI for xen-devel@lists.xenproject.org; Wed, 22 Jun 2016 11:19:32 +0000 Received: from [85.158.137.68] by server-13.bemta-3.messagelabs.com id 23/15-20705-3447A675; Wed, 22 Jun 2016 11:19:31 +0000 X-Brightmail-Tracker: H4sIAAAAAAAAA+NgFlrKIsWRWlGSWpSXmKPExsXitHRDpK5TSVa 4weRL5hbft0xmcmD0OPzhCksAYxRrZl5SfkUCa8bLzX4F94wrzm5sZG1gbNLuYuTkkBDwlzh4 cy8LiC0skCzx7uhTRhBbRKBaYs6/X6xdjFwcQgItjBIf/n4HSnBwMAsoS2x4IA1SwyagI/F4y Qx2EJtXQFNi1dpdbCAlLAKqEp+uqoKERQWCJe5ceM4GUSIocXLmE7BVnAJaEg8bVkJN1JRYv0 sfJMwsIC+x/e0cZhBbSEBF4uPaVawQV3JL3D49lXkCI/8sJJNmIXTPQtK9gJF5FaNGcWpRWWq RrqGxXlJRZnpGSW5iZo6uoYGxXm5qcXFiempOYlKxXnJ+7iZGYPAxAMEOxm3bPQ8xSnIwKYny yitnhQvxJeWnVGYkFmfEF5XmpBYfYpTh4FCS4O0vAsoJFqWmp1akZeYA4wAmLcHBoyTCa1wMl OYtLkjMLc5Mh0idYlSUEuf9B9InAJLIKM2Da4PF3iVGWSlhXkagQ4R4ClKLcjNLUOVfMYpzMC oJ854FmcKTmVcCN/0V0GImoMXL+tNBFpckIqSkGhhVb8TNjjQ4dyBF+dEO+08n9rz66xB8Lr7 2ytKTBsFOEz4XW4Un9VY83fTR51CrsVX97GZZndRTq9ijeJa80J0quHxOU5fHUbcggcR1B802 WJ9hWqqp8WU9347eE1zRWfL1N9/43T+jGPnFf5OWR7rBpbgDx6YV7DP7cPFtcQL/leCi2IBt/ sFKLMUZiYZazEXFiQAS1WeQuAIAAA== X-Env-Sender: prvs=9743e3323=david.vrabel@citrix.com X-Msg-Ref: server-2.tower-31.messagelabs.com!1466594369!46586631!1 X-Originating-IP: [66.165.176.89] X-SpamReason: No, hits=0.0 required=7.0 tests=sa_preprocessor: VHJ1c3RlZCBJUDogNjYuMTY1LjE3Ni44OSA9PiAyMDMwMDc=\n, received_headers: No Received headers X-StarScan-Received: X-StarScan-Version: 8.46; banners=-,-,- X-VirusChecked: Checked Received: (qmail 25627 invoked from network); 22 Jun 2016 11:19:30 -0000 Received: from smtp.citrix.com (HELO SMTP.CITRIX.COM) (66.165.176.89) by server-2.tower-31.messagelabs.com with RC4-SHA encrypted SMTP; 22 Jun 2016 11:19:30 -0000 X-IronPort-AV: E=Sophos;i="5.26,509,1459814400"; d="scan'208";a="362050964" To: David Vrabel , Boris Ostrovsky , References: <1466525353-27751-1-git-send-email-david.vrabel@citrix.com> <57699624.4060500@oracle.com> <576A6E6A.8030502@citrix.com> From: David Vrabel Message-ID: <576A743E.8070006@citrix.com> Date: Wed, 22 Jun 2016 12:19:26 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Icedove/38.5.0 MIME-Version: 1.0 In-Reply-To: <576A6E6A.8030502@citrix.com> X-DLP: MIA2 Cc: Juergen Gross Subject: Re: [Xen-devel] [PATCHv2] x86/xen: avoid m2p lookup when setting early page table entries X-BeenThere: xen-devel@lists.xen.org X-Mailman-Version: 2.1.18 Precedence: list List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xen.org Sender: "Xen-devel" X-Virus-Scanned: ClamAV using ClamSMTP On 22/06/16 11:54, David Vrabel wrote: > On 21/06/16 20:31, Boris Ostrovsky wrote: >> On 06/21/2016 12:09 PM, David Vrabel wrote: >>> When page tables entries are set using xen_set_pte_init() during early >>> boot there is no page fault handler that could handle a fault when >>> performing an M2P lookup. >>> >>> In 64 guest (usually dom0) early_ioremap() would fault in >>> xen_set_pte_init() because an M2P lookup faults because the MFN is in >>> MMIO space and not mapped in the M2P. This lookup is done to see if >>> the PFN in in the range used for the initial page table pages, so that >>> the PTE may be set as read-only. >>> >>> The M2P lookup can be avoided by moving the check (and clear of RW) >>> earlier when the PFN is still available. > [...] >>> --- a/arch/x86/xen/mmu.c >>> +++ b/arch/x86/xen/mmu.c >>> @@ -1562,7 +1562,7 @@ static pte_t __init mask_rw_pte(pte_t *ptep, pte_t pte) >>> return pte; >>> } >>> #else /* CONFIG_X86_64 */ >>> -static pte_t __init mask_rw_pte(pte_t *ptep, pte_t pte) >>> +static pteval_t __init mask_rw_pte(pteval_t pte) >>> { >>> unsigned long pfn; >>> >>> @@ -1577,10 +1577,10 @@ static pte_t __init mask_rw_pte(pte_t *ptep, pte_t pte) >>> * page tables for mapping the p2m list, too, and page tables MUST be >>> * mapped read-only. >>> */ >>> - pfn = pte_pfn(pte); >>> + pfn = (pte & PTE_PFN_MASK) >> PAGE_SHIFT; >> >> Is it obvious that we are holding valid PFN at this point? It wasn't >> immediately obvious to me so I wonder whether a comment stating this >> would be useful here (yes, you mention it in the commit messages). > > I don't understand what you mean by a "valid PFN"? > > This is only called from xen_make_pte_init() which is for converting > ptevals containing PFNs to MFNs. Did that answer your question? > > Would it be clearer if I just inlined the two functions like so: It would help if I included the right diff. 8<--------------------- x86/xen: avoid m2p lookup when setting early page table entries When page tables entries are set using xen_set_pte_init() during early boot there is no page fault handler that could handle a fault when performing an M2P lookup. In 64 guest (usually dom0) early_ioremap() would fault in xen_set_pte_init() because an M2P lookup faults because the MFN is in MMIO space and not mapped in the M2P. This lookup is done to see if the PFN in in the range used for the initial page table pages, so that the PTE may be set as read-only. The M2P lookup can be avoided by moving the check (and clear of RW) earlier when the PFN is still available. Signed-off-by: David Vrabel Tested-by: Keven Moraga --- v3: - fold mask_rw_pte()/mask_rw_pteval() into their callers. v2: - Remove __init annotation from xen_make_pte_init() since PV_CALLEE_SAVE_REGS_THUNK always puts the thunk in .text. - mask_rw_pte() -> mask_rw_pteval() for x86-64. --- arch/x86/xen/mmu.c | 76 +++++++++++++++++++++++++----------------------------- 1 file changed, 35 insertions(+), 41 deletions(-) * doesn't allow RO page table pages to be remapped RW. @@ -1600,13 +1565,41 @@ static pte_t __init mask_rw_pte(pte_t *ptep, pte_t pte) * so always write the PTE directly and rely on Xen trapping and * emulating any updates as necessary. */ -static void __init xen_set_pte_init(pte_t *ptep, pte_t pte) +__visible pte_t xen_make_pte_init(pteval_t pte) { - if (pte_mfn(pte) != INVALID_P2M_ENTRY) - pte = mask_rw_pte(ptep, pte); - else - pte = __pte_ma(0); +#ifdef CONFIG_X86_64 + unsigned long pfn; + + /* + * Pages belonging to the initial p2m list mapped outside the default + * address range must be mapped read-only. This region contains the + * page tables for mapping the p2m list, too, and page tables MUST be + * mapped read-only. + */ + pfn = (pte & PTE_PFN_MASK) >> PAGE_SHIFT; + if (xen_start_info->mfn_list < __START_KERNEL_map && + pfn >= xen_start_info->first_p2m_pfn && + pfn < xen_start_info->first_p2m_pfn + xen_start_info->nr_p2m_frames) + pte &= ~_PAGE_RW; +#endif + pte = pte_pfn_to_mfn(pte); + if ((pte & PTE_PFN_MASK) >> PAGE_SHIFT == INVALID_P2M_ENTRY) + pte = 0; + + return native_make_pte(pte); +} +PV_CALLEE_SAVE_REGS_THUNK(xen_make_pte_init); + +static void __init xen_set_pte_init(pte_t *ptep, pte_t pte) +{ +#ifdef CONFIG_X86_32 + /* If there's an existing pte, then don't allow _PAGE_RW to be set */ + if (pte_mfn(pte) != INVALID_P2M_ENTRY + && pte_val_ma(*ptep) & _PAGE_PRESENT) + pte = __pte_ma(((pte_val_ma(*ptep) & _PAGE_RW) | ~_PAGE_RW) & + pte_val_ma(pte)); +#endif native_set_pte(ptep, pte); } @@ -2407,6 +2400,7 @@ static void __init xen_post_allocator_init(void) pv_mmu_ops.alloc_pud = xen_alloc_pud; pv_mmu_ops.release_pud = xen_release_pud; #endif + pv_mmu_ops.make_pte = PV_CALLEE_SAVE(xen_make_pte); #ifdef CONFIG_X86_64 pv_mmu_ops.write_cr3 = &xen_write_cr3; @@ -2455,7 +2449,7 @@ static const struct pv_mmu_ops xen_mmu_ops __initconst = { .pte_val = PV_CALLEE_SAVE(xen_pte_val), .pgd_val = PV_CALLEE_SAVE(xen_pgd_val), - .make_pte = PV_CALLEE_SAVE(xen_make_pte), + .make_pte = PV_CALLEE_SAVE(xen_make_pte_init), .make_pgd = PV_CALLEE_SAVE(xen_make_pgd), #ifdef CONFIG_X86_PAE diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c index 478a2de..64d8f0b 100644 --- a/arch/x86/xen/mmu.c +++ b/arch/x86/xen/mmu.c @@ -1551,41 +1551,6 @@ static void xen_pgd_free(struct mm_struct *mm, pgd_t *pgd) #endif } -#ifdef CONFIG_X86_32 -static pte_t __init mask_rw_pte(pte_t *ptep, pte_t pte) -{ - /* If there's an existing pte, then don't allow _PAGE_RW to be set */ - if (pte_val_ma(*ptep) & _PAGE_PRESENT) - pte = __pte_ma(((pte_val_ma(*ptep) & _PAGE_RW) | ~_PAGE_RW) & - pte_val_ma(pte)); - - return pte; -} -#else /* CONFIG_X86_64 */ -static pte_t __init mask_rw_pte(pte_t *ptep, pte_t pte) -{ - unsigned long pfn; - - if (xen_feature(XENFEAT_writable_page_tables) || - xen_feature(XENFEAT_auto_translated_physmap) || - xen_start_info->mfn_list >= __START_KERNEL_map) - return pte; - - /* - * Pages belonging to the initial p2m list mapped outside the default - * address range must be mapped read-only. This region contains the - * page tables for mapping the p2m list, too, and page tables MUST be - * mapped read-only. - */ - pfn = pte_pfn(pte); - if (pfn >= xen_start_info->first_p2m_pfn && - pfn < xen_start_info->first_p2m_pfn + xen_start_info->nr_p2m_frames) - pte = __pte_ma(pte_val_ma(pte) & ~_PAGE_RW); - - return pte; -} -#endif /* CONFIG_X86_64 */ - /* * Init-time set_pte while constructing initial pagetables, which