From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ob0-f178.google.com (mail-ob0-f178.google.com [209.85.214.178]) by kanga.kvack.org (Postfix) with ESMTP id 2B29F6B0253 for ; Mon, 25 Jan 2016 12:46:58 -0500 (EST) Received: by mail-ob0-f178.google.com with SMTP id zv1so20907633obb.2 for ; Mon, 25 Jan 2016 09:46:58 -0800 (PST) Received: from mail-ob0-x235.google.com (mail-ob0-x235.google.com. [2607:f8b0:4003:c01::235]) by mx.google.com with ESMTPS id ol1si18450319obc.17.2016.01.25.09.46.57 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 25 Jan 2016 09:46:57 -0800 (PST) Received: by mail-ob0-x235.google.com with SMTP id vt7so122245605obb.1 for ; Mon, 25 Jan 2016 09:46:57 -0800 (PST) MIME-Version: 1.0 In-Reply-To: References: <1453742717-10326-1-git-send-email-matthew.r.wilcox@intel.com> <1453742717-10326-2-git-send-email-matthew.r.wilcox@intel.com> From: Andy Lutomirski Date: Mon, 25 Jan 2016 09:46:37 -0800 Message-ID: Subject: Re: [PATCH 1/3] x86: Honour passed pgprot in track_pfn_insert() and track_pfn_remap() Content-Type: text/plain; charset=UTF-8 Sender: owner-linux-mm@kvack.org List-ID: To: Matthew Wilcox Cc: Ingo Molnar , Matthew Wilcox , Kees Cook , Andrew Morton , "linux-kernel@vger.kernel.org" , "linux-mm@kvack.org" On Mon, Jan 25, 2016 at 9:33 AM, Andy Lutomirski wrote: > On Mon, Jan 25, 2016 at 9:25 AM, Matthew Wilcox > wrote: >> From: Matthew Wilcox >> >> track_pfn_insert() overwrites the pgprot that is passed in with a value >> based on the VMA's page_prot. This is a problem for people trying to >> do clever things with the new vm_insert_pfn_prot() as it will simply >> overwrite the passed protection flags. If we use the current value of >> the pgprot as the base, then it will behave as people are expecting. >> >> Also fix track_pfn_remap() in the same way. > > Well that's embarrassing. Presumably it worked for me because I only > overrode the cacheability bits and lookup_memtype did the right thing. > > But shouldn't the PAT code change the memtype if vm_insert_pfn_prot > requests it? Or are there no callers that actually need that? (HPET > doesn't, because there's a plain old ioremapped mapping.) > Looking a bit further, track_pfn_remap does this, while track_pfn_insert does not. I don't know why I'm also a bit confused as to how any of this works. There doesn't seem to be any reference counting of memtypes, so I don't understand why, say, remapping the same range twice and then freeing them in FIFO order doesn't break the memtype code. (There's VM_PAT, but that seems likely to be extremely fragile.) --Andy -- 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