Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753881AbeAKXDY (ORCPT + 1 other); Thu, 11 Jan 2018 18:03:24 -0500 Received: from Galois.linutronix.de ([146.0.238.70]:60293 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750782AbeAKXDV (ORCPT ); Thu, 11 Jan 2018 18:03:21 -0500 Date: Fri, 12 Jan 2018 00:03:10 +0100 (CET) From: Thomas Gleixner To: Linus Torvalds cc: 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 , Steve Sistare , Matt Fleming , Borislav Petkov Subject: Re: [PATCH 4.4 00/37] 4.4.110-stable review In-Reply-To: Message-ID: References: <20180105175229.GA29834@kroah.com> <20180105204557.GA8839@kroah.com> <20180107104540.GB14783@kroah.com> <20180108074645.GA24062@kroah.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, 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 But there is one very well hidden user for it after boot: It's used for booting secondary CPUs from real mode So the transition to long mode for secondaries uses the trampoline pgd for long mode transition and then jumping to secondary_startup_64 where CR3 is set to the real kernel page tables. Thanks, tglx