From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753984AbbJ0Cd7 (ORCPT ); Mon, 26 Oct 2015 22:33:59 -0400 Received: from mail-io0-f181.google.com ([209.85.223.181]:34787 "EHLO mail-io0-f181.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751871AbbJ0Cd4 (ORCPT ); Mon, 26 Oct 2015 22:33:56 -0400 MIME-Version: 1.0 In-Reply-To: <20151026210235.GA3526@codeblueprint.co.uk> References: <1445593826-4578-1-git-send-email-izumi.taku@jp.fujitsu.com> <20151026210235.GA3526@codeblueprint.co.uk> Date: Tue, 27 Oct 2015 11:33:55 +0900 Message-ID: Subject: Re: [PATCH v2] efi: Fix warning of int-to-pointer-cast on x86 32-bit builds From: Ard Biesheuvel To: Matt Fleming Cc: Taku Izumi , Ingo Molnar , "linux-kernel@vger.kernel.org" , kamezawa.hiroyu@jp.fujitsu.com, "linux-efi@vger.kernel.org" Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 27 October 2015 at 06:02, Matt Fleming wrote: > On Fri, 23 Oct, at 10:37:46AM, Ard Biesheuvel wrote: >> >> After looking at the original (already merged) patch 11/11 again, I >> realize this is still not right: the problem is that efi_memory_map's >> phys_map member uses a void* type to hold a physical address, which >> happens to be correct in the normal case even when phys_addr_t is >> larger than void* (like on ARM with LPAE enabled) since the address it >> holds is the address of an allocation performed by the firmware, which >> only uses 1:1 addressable memory. >> >> However, overwriting memmap.phys_map with a value produced my >> memblock_alloc() is problematic, since the allocation may be above 4 >> GB on 32-bit (L)PAE platforms. So the correct way to do this would be >> to set the memblock limit to 4GB before memblock_alloc() on 32-bit >> platforms, and restore it afterwards. This is a bit of a kludge, >> though, and it would be more correct to change the type of >> efi_memory_map::phys_map to phys_addr_t, although I don't know what >> the potential fallout of that change is. Matt? > > I think that should be fine. The only potentially tricky situation we > could encounter is where 32-bit x86 firmware uses PAE but the kernel > is built without support. > > But that's not something I've ever seen enabled in the firmware and > there's a bunch of assumptions in the kernel already that would break > in that case. > Does UEFI even allow that? Even if it can describe memory over 4 GB, it uses a flat mapping so allocations done by the stub (which retrieves the memory map) should never reside at addresses over 4 GB. -- Ard.