From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ed1-f70.google.com (mail-ed1-f70.google.com [209.85.208.70]) by kanga.kvack.org (Postfix) with ESMTP id 46D0A6B582A for ; Fri, 30 Nov 2018 07:19:43 -0500 (EST) Received: by mail-ed1-f70.google.com with SMTP id c53so2795419edc.9 for ; Fri, 30 Nov 2018 04:19:43 -0800 (PST) Received: from mx1.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id a19si2295499edt.34.2018.11.30.04.19.41 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 30 Nov 2018 04:19:42 -0800 (PST) Subject: Re: [PATCH 1/2] x86/mm: Fix guard hole handling References: <20181130115758.4425-1-kirill.shutemov@linux.intel.com> <20181130115758.4425-2-kirill.shutemov@linux.intel.com> <76b8ca15-405a-055f-41b3-532b116c3a8b@suse.com> <20181130121131.g3xvlvixv7mvlr7b@black.fi.intel.com> From: Juergen Gross Message-ID: Date: Fri, 30 Nov 2018 13:19:40 +0100 MIME-Version: 1.0 In-Reply-To: <20181130121131.g3xvlvixv7mvlr7b@black.fi.intel.com> Content-Type: text/plain; charset=utf-8 Content-Language: de-DE Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: "Kirill A. Shutemov" Cc: tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, hpa@zytor.com, dave.hansen@linux.intel.com, luto@kernel.org, peterz@infradead.org, boris.ostrovsky@oracle.com, bhe@redhat.com, x86@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org On 30/11/2018 13:11, Kirill A. Shutemov wrote: > On Fri, Nov 30, 2018 at 12:03:33PM +0000, Juergen Gross wrote: >> On 30/11/2018 12:57, Kirill A. Shutemov wrote: >>> There is a guard hole at the beginning of kernel address space, also >>> used by hypervisors. It occupies 16 PGD entries. >>> >>> We do not state the reserved range directly, but calculate it relative >>> to other entities: direct mapping and user space ranges. >>> >>> The calculation got broken by recent change in kernel memory layout: LDT >>> remap range is now mapped before direct mapping and makes the calculation >>> invalid. >>> >>> The breakage leads to crash on Xen dom0 boot[1]. >>> >>> State the reserved range directly. It's part of kernel ABI (hypervisors >>> expect it to be stable) and must not depend on changes in the rest of >>> kernel memory layout. >>> >>> [1] https://lists.xenproject.org/archives/html/xen-devel/2018-11/msg03313.html >>> >>> Signed-off-by: Kirill A. Shutemov >>> Reported-by: Hans van Kranenburg >>> Fixes: d52888aa2753 ("x86/mm: Move LDT remap out of KASLR region on 5-level paging") >>> --- >>> arch/x86/include/asm/pgtable_64_types.h | 5 +++++ >>> arch/x86/mm/dump_pagetables.c | 8 ++++---- >>> arch/x86/xen/mmu_pv.c | 11 ++++++----- >>> 3 files changed, 15 insertions(+), 9 deletions(-) >>> >>> diff --git a/arch/x86/include/asm/pgtable_64_types.h b/arch/x86/include/asm/pgtable_64_types.h >>> index 84bd9bdc1987..13aef22cee18 100644 >>> --- a/arch/x86/include/asm/pgtable_64_types.h >>> +++ b/arch/x86/include/asm/pgtable_64_types.h >>> @@ -111,6 +111,11 @@ extern unsigned int ptrs_per_p4d; >>> */ >>> #define MAXMEM (1UL << MAX_PHYSMEM_BITS) >>> >>> +#define GUARD_HOLE_PGD_ENTRY -256UL >>> +#define GUARD_HOLE_SIZE (16UL << PGDIR_SHIFT) >>> +#define GUARD_HOLE_BASE_ADDR (LDT_PGD_ENTRY << PGDIR_SHIFT) >> >> s/LDT_PGD_ENTRY/GUARD_HOLE_PGD_ENTRY/ > > Ughh.. > >>>>From 4308d560cc2874a9f596512bcb4c601b2450653d Mon Sep 17 00:00:00 2001 > From: "Kirill A. Shutemov" > Date: Fri, 30 Nov 2018 14:29:42 +0300 > Subject: [PATCH 1/2] x86/mm: Fix guard hole handling > > There is a guard hole at the beginning of kernel address space, also > used by hypervisors. It occupies 16 PGD entries. > > We do not state the reserved range directly, but calculate it relative > to other entities: direct mapping and user space ranges. > > The calculation got broken by recent change in kernel memory layout: LDT > remap range is now mapped before direct mapping and makes the calculation > invalid. > > The breakage leads to crash on Xen dom0 boot[1]. > > State the reserved range directly. It's part of kernel ABI (hypervisors > expect it to be stable) and must not depend on changes in the rest of > kernel memory layout. > > [1] https://lists.xenproject.org/archives/html/xen-devel/2018-11/msg03313.html > > Signed-off-by: Kirill A. Shutemov > Reported-by: Hans van Kranenburg > Fixes: d52888aa2753 ("x86/mm: Move LDT remap out of KASLR region on 5-level paging") > Signed-off-by: Kirill A. Shutemov Reviewed-by: Juergen Gross Juergen