From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752428AbdHPQPG (ORCPT ); Wed, 16 Aug 2017 12:15:06 -0400 Received: from mail.kernel.org ([198.145.29.99]:57900 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751692AbdHPQPD (ORCPT ); Wed, 16 Aug 2017 12:15:03 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 73B7D22BE3 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=luto@kernel.org MIME-Version: 1.0 In-Reply-To: <20170816125715.GB3384@codeblueprint.co.uk> References: <1502824706-30762-1-git-send-email-sai.praneeth.prakhya@intel.com> <1502824706-30762-4-git-send-email-sai.praneeth.prakhya@intel.com> <20170816095338.GB17270@leverpostej> <20170816100709.GG12845@arm.com> <20170816110321.GC17270@leverpostej> <20170816125715.GB3384@codeblueprint.co.uk> From: Andy Lutomirski Date: Wed, 16 Aug 2017 09:14:41 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH 3/3] x86/efi: Use efi_switch_mm() rather than manually twiddling with cr3 To: Matt Fleming Cc: Mark Rutland , Will Deacon , Ard Biesheuvel , Andy Lutomirski , Sai Praneeth Prakhya , Peter Zijlstra , "linux-efi@vger.kernel.org" , "linux-kernel@vger.kernel.org" , joeyli , Borislav Petkov , "Michael S. Tsirkin" , "Neri, Ricardo" , "Ravi V. Shankar" 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 Wed, Aug 16, 2017 at 5:57 AM, Matt Fleming wrote: > On Wed, 16 Aug, at 12:03:22PM, Mark Rutland wrote: >> >> I'd expect we'd abort at a higher level, not taking any sample. i.e. >> we'd have the core overflow handler check in_funny_mm(), and if so, skip >> the sample, as with the skid case. > > FYI, this is my preferred solution for x86 too. One option for the "funny mm" flag would be literally the condition current->mm != current->active_mm. I *think* this gets all the cases right as long as efi_switch_mm is careful with its ordering and that the arch switch_mm() code can handle the resulting ordering. (x86's can now, I think, or at least will be able to in 4.14 -- not sure about other arches). That being said, there's a totally different solution: run EFI callbacks in a kernel thread. This has other benefits: we could run those callbacks in user mode some day, and doing *that* in a user thread seems like a mistake. --Andy