From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx172.postini.com [74.125.245.172]) by kanga.kvack.org (Postfix) with SMTP id 83BF26B005D for ; Wed, 3 Oct 2012 01:20:36 -0400 (EDT) Message-ID: <506BC96D.10507@hp.com> Date: Tue, 02 Oct 2012 23:13:17 -0600 From: Thavatchai Makphaibulchoke MIME-Version: 1.0 Subject: Re: [PATCH] Fix devmem_is_allowed for below 1MB accesses for an efi machine References: <1349213536-3436-1-git-send-email-tmac@hp.com> <506B6191.6080605@zytor.com> <20121003043116.GA26241@srcf.ucam.org> <506BC2A0.8060500@zytor.com> <20121003051522.GA27113@srcf.ucam.org> In-Reply-To: <20121003051522.GA27113@srcf.ucam.org> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Matthew Garrett Cc: "H. Peter Anvin" , T Makphaibulchoke , tglx@linutronix.de, mingo@redhat.com, x86@kernel.org, akpm@linux-foundation.org, yinghai@kernel.org, tiwai@suse.de, viro@zeniv.linux.org.uk, aarcange@redhat.com, tony.luck@intel.com, mgorman@suse.de, weiyang@linux.vnet.ibm.com, octavian.purdila@intel.com, paul.gortmaker@windriver.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org Thank you both for the comments. Sounds like a better solution is to allow accesses to only I/O regions presented in the EFI memory map for physical addresses below 1 MB. Do we need to worry about the X checksum in the first MB on an EFI system? Thanks, Mak. On 10/02/2012 11:15 PM, Matthew Garrett wrote: > On Tue, Oct 02, 2012 at 09:44:16PM -0700, H. Peter Anvin wrote: > >> We *always* expose the I/O regions to /dev/mem. That is what /dev/mem >> *does*. The above is an exception (which is really obsolete, too: we >> should simply disallow access to anything which is treated as system >> RAM, which doesn't include the BIOS regions in question; the only reason >> we don't is that some versions of X take a checksum of the RAM in the >> first megabyte as some kind of idiotic random seed.) > > Oh, right, got you. In that case I think we potentially need a > finer-grained check on EFI platforms - the EFI memory map is kind enough > to tell us the difference between unusable regions and io regions, and > we could avoid access to the unusable ones. > -- 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