Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756534Ab3DZPyH (ORCPT ); Fri, 26 Apr 2013 11:54:07 -0400 Received: from service87.mimecast.com ([91.220.42.44]:51465 "EHLO service87.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753631Ab3DZPyF convert rfc822-to-8bit (ORCPT ); Fri, 26 Apr 2013 11:54:05 -0400 Message-ID: <517AA319.5070709@arm.com> Date: Fri, 26 Apr 2013 16:54:01 +0100 From: Marc Zyngier User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130330 Thunderbird/17.0.5 MIME-Version: 1.0 To: Arnd Bergmann CC: Anup Patel , Peter Maydell , "linaro-kernel@lists.linaro.org" , "patches@linaro.org" , Alexander Graf , "linux-kernel@vger.kernel.org List" , "kvmarm@lists.cs.columbia.edu" , "linux-arm-kernel@lists.infradead.org" Subject: Re: [PATCH 0/2] Early printk support for virtio console devices. References: <1366974299-17877-1-git-send-email-pranavkumar@linaro.org> <1577576.O1Cm2pf5KD@wuerfel> <201304261703.17798.arnd@arndb.de> In-Reply-To: <201304261703.17798.arnd@arndb.de> X-Enigmail-Version: 1.4.6 X-OriginalArrivalTime: 26 Apr 2013 15:54:01.0890 (UTC) FILETIME=[45808020:01CE4296] X-MC-Unique: 113042616540205501 Content-Type: text/plain; charset=WINDOWS-1252 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1403 Lines: 33 On 26/04/13 16:03, Arnd Bergmann wrote: > On Friday 26 April 2013, Anup Patel wrote: >> I am curious about how smh-based or hypercall-based early prints would >> be handled in following scenario: >> >> "A board is running KVM ARM enabled kernel and linux console on serial >> port. Now a user remotely connects to the board via telnet/ssh and >> launches a VM with smh-based or hypercall-based earlyprintk." >> >> In the above scenario, will smh-based or hypercall-based earlyprints >> appear to user on remote shell or not ? > > The implementation of the console device would still be done by KVM, > as for any other virtual device, so it shows up whereever kvm is > configured to output the console data. Actually, at least in the case of smh-based earlyprintk, the output only appears in the model console, and never reach the rest of the kernel. And any other non-MMIO approach (like a hypercall) will be very hard to feed back to the console, as KVM itself has no idea of what a "console" is. You'd need another side channel to userspace, hoping that it will be able to merge the multiple streams. M. -- Jazz is not dead. It just smells funny... -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/