From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756557AbcBCLdQ (ORCPT ); Wed, 3 Feb 2016 06:33:16 -0500 Received: from mail-ig0-f170.google.com ([209.85.213.170]:37472 "EHLO mail-ig0-f170.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756406AbcBCLdM (ORCPT ); Wed, 3 Feb 2016 06:33:12 -0500 MIME-Version: 1.0 In-Reply-To: <20160203105851.GA22159@gmail.com> References: <1454364428-494-1-git-send-email-matt@codeblueprint.co.uk> <1454364428-494-8-git-send-email-matt@codeblueprint.co.uk> <20160203094340.GA15890@gmail.com> <20160203105851.GA22159@gmail.com> Date: Wed, 3 Feb 2016 12:33:10 +0100 Message-ID: Subject: Re: [PATCH 07/14] efi: runtime-wrappers: Run UEFI Runtime Services with interrupts enabled From: Ard Biesheuvel To: Ingo Molnar Cc: Matt Fleming , "H . Peter Anvin" , Thomas Gleixner , "linux-efi@vger.kernel.org" , "linux-kernel@vger.kernel.org" , Linus Torvalds , Andy Lutomirski , Peter Zijlstra 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 3 February 2016 at 11:58, Ingo Molnar wrote: > > * Ard Biesheuvel wrote: > >> > More fundamentally, this makes me nervous: >> > >> > > The UEFI spec allows Runtime Services to be invoked with interrupts >> > > enabled. [...] >> > >> > So what really matters is not what the spec says, but how Windows executes >> > UEFI firmware code in practice. >> > >> > If major versions of Windows calls UEFI firmware with interrupts disabled, >> > then frankly I don't think we should interrupt them under Linux either, >> > regardless of what the spec says ... >> > >> > Random firmware code getting interrupted by the OS changes timings and might >> > have other side effects the firmware code might not expect - so the question >> > is, does Windows already de facto allow the IRQ preemption of firmware calls? >> > >> >> Good question. I will try to find out. > > Note that if there's a reasonable (but not 100%) case in favor of keeping irqs > enabled, we can try your patch, with the possibility that we might have to revert > it, should it cause problems. > I think this might have been the reason Matt wanted this in -next early, but I will let him confirm whether that was the case. > In practice we probably already interrupt EFI services with NMI interrupts, which > can be pretty heavy as well if they for example generate printks. > > So I'm not against this change in a strong fashion - I'm just a bit cautious and > it would be nice to know how Windows behaves here. > I am not sure how yet, but I am going to try and figure out what Windows does. I suppose hacking OVMF to record some IRQ mask information when RT services are being invoked should be sufficient, but I am going to need some help from someone that understands OVMF and x86 (Matt?)