From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dave Hansen Subject: Re: [PATCH 1/2] x86/efi: Unmap efi boot services code/data regions from efi_pgd Date: Mon, 22 Oct 2018 07:12:25 -0700 Message-ID: References: <1540172145-17134-1-git-send-email-sai.praneeth.prakhya@intel.com> <1540172145-17134-2-git-send-email-sai.praneeth.prakhya@intel.com> <20181022015738.GB24095@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Return-path: In-Reply-To: <20181022015738.GB24095@gmail.com> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org To: Ingo Molnar , Sai Praneeth Prakhya Cc: linux-efi@vger.kernel.org, linux-kernel@vger.kernel.org, x86@kernel.org, Borislav Petkov , Andy Lutomirski , Bhupesh Sharma , Thomas Gleixner , Peter Zijlstra , Ard Biesheuvel , Peter Zijlstra List-Id: linux-efi@vger.kernel.org On 10/21/2018 06:57 PM, Ingo Molnar wrote: > Does the CPU _ever_ look look at the PFN if the page is !_PAGE_PRESENT, > for example speculatively? If yes then what is the recommended value for > the pfn - zero perhaps? I'll never say never. :) For L1TF[1], we know the CPU did exactly this; it ignored the _PAGE_PRESENT bit when fetching data from the L1. That's what is worked around with the gunk in arch/x86/include/asm/pgtable-invert.h. I think Andi plugged the code in here at a low enough level in the page table manipulation that pageattr.c should inherit it without doing anything explicit. But, Sai, you might want to double-check this. 1. https://www.intel.com/content/www/us/en/architecture-and-technology/l1tf.html