From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755591AbdERP7W (ORCPT ); Thu, 18 May 2017 11:59:22 -0400 Received: from mx2.suse.de ([195.135.220.15]:33181 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1755402AbdERP7T (ORCPT ); Thu, 18 May 2017 11:59:19 -0400 Date: Thu, 18 May 2017 17:59:14 +0200 From: Michal Hocko To: "Kirill A. Shutemov" Cc: "Kirill A. Shutemov" , x86@kernel.org, Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , Andi Kleen , Dave Hansen , Andy Lutomirski , Dan Williams , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-api@vger.kernel.org Subject: Re: [PATCHv5, REBASED 9/9] x86/mm: Allow to have userspace mappings above 47-bits Message-ID: <20170518155914.GC18333@dhcp22.suse.cz> References: <20170515121218.27610-1-kirill.shutemov@linux.intel.com> <20170515121218.27610-10-kirill.shutemov@linux.intel.com> <20170518114359.GB25471@dhcp22.suse.cz> <20170518151952.jzvz6aeelgx7ifmm@node.shutemov.name> <20170518152736.GA18333@dhcp22.suse.cz> <20170518154135.zekuqls6almevrjt@node.shutemov.name> <20170518155003.GB18333@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170518155003.GB18333@dhcp22.suse.cz> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu 18-05-17 17:50:03, Michal Hocko wrote: > On Thu 18-05-17 18:41:35, Kirill A. Shutemov wrote: > > On Thu, May 18, 2017 at 05:27:36PM +0200, Michal Hocko wrote: > > > On Thu 18-05-17 18:19:52, Kirill A. Shutemov wrote: > > > > On Thu, May 18, 2017 at 01:43:59PM +0200, Michal Hocko wrote: > > > > > On Mon 15-05-17 15:12:18, Kirill A. Shutemov wrote: > > > > > [...] > > > > > > @@ -195,6 +207,16 @@ arch_get_unmapped_area_topdown(struct file *filp, const unsigned long addr0, > > > > > > info.length = len; > > > > > > info.low_limit = PAGE_SIZE; > > > > > > info.high_limit = get_mmap_base(0); > > > > > > + > > > > > > + /* > > > > > > + * If hint address is above DEFAULT_MAP_WINDOW, look for unmapped area > > > > > > + * in the full address space. > > > > > > + * > > > > > > + * !in_compat_syscall() check to avoid high addresses for x32. > > > > > > + */ > > > > > > + if (addr > DEFAULT_MAP_WINDOW && !in_compat_syscall()) > > > > > > + info.high_limit += TASK_SIZE_MAX - DEFAULT_MAP_WINDOW; > > > > > > + > > > > > > info.align_mask = 0; > > > > > > info.align_offset = pgoff << PAGE_SHIFT; > > > > > > if (filp) { > > > > > > > > > > I have two questions/concerns here. The above assumes that any address above > > > > > 1<<47 will use the _whole_ address space. Is this what we want? > > > > > > > > Yes, I believe so. > > > > > > > > > What if somebody does mmap(1<<52, ...) because he wants to (ab)use 53+ > > > > > bits for some other purpose? Shouldn't we cap the high_limit by the > > > > > given address? > > > > > > > > This would screw existing semantics of hint address -- "map here if > > > > free, please". > > > > > > Well, the given address is just _hint_. We are still allowed to map to a > > > different place. And it is not specified whether the resulting mapping > > > is above or below that address. So I do not think it would screw the > > > existing semantic. Or do I miss something? > > > > You are right, that this behaviour is not fixed by any standard or written > > down in documentation, but it's de-facto policy of Linux mmap(2) the > > beginning. > > > > And we need to be very careful when messing with this. > > I am sorry but I still do not understand. You already touch this > semantic. mmap(-1UL,...) will already returns basically arbitrary > address. All I am asking for is that mmap doesn't return higher address > than the given one whent address > 1<<47. We do not have any such users > currently so it won't be a change in behavior while it would allow > different sized address spaces naturally. I basically mean something like the following --- diff --git a/arch/x86/kernel/sys_x86_64.c b/arch/x86/kernel/sys_x86_64.c index 74d1587b181d..d6f66ff02d0a 100644 --- a/arch/x86/kernel/sys_x86_64.c +++ b/arch/x86/kernel/sys_x86_64.c @@ -195,7 +195,7 @@ arch_get_unmapped_area_topdown(struct file *filp, const unsigned long addr0, goto bottomup; /* requesting a specific address */ - if (addr) { + if (addr && addr <= DEFAULT_MAP_WINDOW) { addr = PAGE_ALIGN(addr); vma = find_vma(mm, addr); if (TASK_SIZE - len >= addr && @@ -215,7 +215,7 @@ arch_get_unmapped_area_topdown(struct file *filp, const unsigned long addr0, * !in_compat_syscall() check to avoid high addresses for x32. */ if (addr > DEFAULT_MAP_WINDOW && !in_compat_syscall()) - info.high_limit += TASK_SIZE_MAX - DEFAULT_MAP_WINDOW; + info.high_limit += min(TASK_SIZE_MAX, address) - DEFAULT_MAP_WINDOW; info.align_mask = 0; info.align_offset = pgoff << PAGE_SHIFT; -- Michal Hocko SUSE Labs