Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933751AbeAKWrk (ORCPT + 1 other); Thu, 11 Jan 2018 17:47:40 -0500 Received: from Galois.linutronix.de ([146.0.238.70]:60263 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933287AbeAKWrj (ORCPT ); Thu, 11 Jan 2018 17:47:39 -0500 Date: Thu, 11 Jan 2018 23:47:23 +0100 (CET) From: Thomas Gleixner To: Steven Sistare cc: Linus Torvalds , Pavel Tatashin , Greg Kroah-Hartman , Andy Lutomirski , Hugh Dickins , Thomas Voegtle , Linux Kernel Mailing List , Andrew Morton , Guenter Roeck , Shuah Khan , patches@kernelci.org, Ben Hutchings , lkft-triage@lists.linaro.org, stable , Matt Fleming , Borislav Petkov Subject: Re: [PATCH 4.4 00/37] 4.4.110-stable review In-Reply-To: <9a74cb17-fdb7-d8c7-cb3a-c7efb436cc81@oracle.com> Message-ID: References: <20180105175229.GA29834@kroah.com> <20180105204557.GA8839@kroah.com> <20180107104540.GB14783@kroah.com> <20180108074645.GA24062@kroah.com> <9a74cb17-fdb7-d8c7-cb3a-c7efb436cc81@oracle.com> User-Agent: Alpine 2.20 (DEB 67 2015-01-07) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Return-Path: On Thu, 11 Jan 2018, Steven Sistare wrote: > On 1/11/2018 5:30 PM, Thomas Gleixner wrote: > > On Thu, 11 Jan 2018, Thomas Gleixner wrote: > >> On Thu, 11 Jan 2018, Linus Torvalds wrote: > >> > >>> On Thu, Jan 11, 2018 at 12:37 PM, Thomas Gleixner wrote: > >>>> > >>>> 67a9108ed431 ("x86/efi: Build our own page table structures") > >>>> > >>>> got rid of EFI depending on real_mode_header->trampoline_pgd > >>> > >>> So I think it only got rid of by default - the codepath is still > >>> there, the allocation is still there, it's just that it's not actually > >>> used unless somebody does that "efi=old_mmap" thing. > >> > >> Yes, the trampoline_pgd is still around, but I can't figure out how it > >> would be used after boot. Confused, digging more. > > > > So coming back to the same commit. From the changelog: > > > > This is caused by mapping EFI regions with RWX permissions. > > There isn't much we can do to restrict the permissions for these > > regions due to the way the firmware toolchains mix code and > > data, but we can at least isolate these mappings so that they do > > not appear in the regular kernel page tables. > > > > In commit d2f7cbe7b26a ("x86/efi: Runtime services virtual > > mapping") we started using 'trampoline_pgd' to map the EFI > > regions because there was an existing identity mapping there > > which we use during the SetVirtualAddressMap() call and for > > broken firmware that accesses those addresses. > > > > So this very commit gets rid of the (ab)use of trampoline_pgd and allocates > > efi_pgd, which we made use the proper size. > > > > trampoline_pgd is since then only used to get into long mode in > > realmode/rm/trampoline_64.S and for reboot in machine_real_restart(). > > > > The runtime services stuff does not use it in kernel versions >= 4.6 > > > > Thanks, > > > > tglx > > Yes, and addressing Linus' concern about EFI_OLD_MEMMAP, those paths are > independent of it. When EFI_OLD_MMAP is enabled, the efi pgd is not > used, and the bug will not bite. We have a fix queued in tip/x86/pti which addresses a missing NX clear, but that's a different story. Thanks, tglx