From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg0-f69.google.com (mail-pg0-f69.google.com [74.125.83.69]) by kanga.kvack.org (Postfix) with ESMTP id F0EDF6B0033 for ; Wed, 1 Nov 2017 14:46:33 -0400 (EDT) Received: by mail-pg0-f69.google.com with SMTP id l24so3240077pgu.17 for ; Wed, 01 Nov 2017 11:46:33 -0700 (PDT) Received: from mga07.intel.com (mga07.intel.com. [134.134.136.100]) by mx.google.com with ESMTPS id n10si260368plp.818.2017.11.01.11.46.32 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 01 Nov 2017 11:46:32 -0700 (PDT) Subject: Re: [PATCH 00/23] KAISER: unmap most of the kernel from userspace page tables References: <20171031223146.6B47C861@viggo.jf.intel.com> <9e45a167-3528-8f93-80bf-c333ae6acb71@linux.intel.com> <8bacac66-7d3e-b15d-a73b-92c55c0b1908@linux.intel.com> From: Dave Hansen Message-ID: <5005a38e-4dbf-d302-9a82-97c92d0f8f07@linux.intel.com> Date: Wed, 1 Nov 2017 11:46:31 -0700 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Linus Torvalds Cc: Andy Lutomirski , Linux Kernel Mailing List , linux-mm , Kees Cook , Hugh Dickins On 11/01/2017 11:27 AM, Linus Torvalds wrote: > So I'd like to see not just the comments about this, but I'd like to > see the code itself actually making that very clear. Have *code* that > verifies that nobody ever tries to use this on a user address (because > that would *completely* screw up all coherency), but also I don't see > why the code possibly looks up the old physical address in ther page > table. Is there _any_ possible reason why you'd want to look up a page > from an old page table? As far as I can tell, we should always know > the physical page we are mapping a priori - we've never re-mapping > random virtual addresses or a highmem page or anything like that. > We're mapping the 1:1 kernel mapping only. The vmalloc()'d stacks definitely need the page table walk. That's yet another thing that will get simpler once we stop needing to map the process stacks. I think there was also a need to do this for the fixmap addresses for the GDT. But, I'm totally with you on making this stuff less generic. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org