Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754071AbbGFJao (ORCPT ); Mon, 6 Jul 2015 05:30:44 -0400 Received: from mail-la0-f45.google.com ([209.85.215.45]:35659 "EHLO mail-la0-f45.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751467AbbGFJa0 (ORCPT ); Mon, 6 Jul 2015 05:30:26 -0400 Date: Mon, 6 Jul 2015 11:30:26 +0200 From: Christoffer Dall To: Andre Przywara Cc: Pavel Fedin , "'Eric Auger'" , "eric.auger@st.com" , "linux-arm-kernel@lists.infradead.org" , Marc Zyngier , "kvmarm@lists.cs.columbia.edu" , "kvm@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "pbonzini@redhat.com" Subject: Re: [PATCH 1/7] KVM: api: add kvm_irq_routing_extended_msi Message-ID: <20150706093026.GA11590@cbox> References: <1435592237-17924-1-git-send-email-eric.auger@linaro.org> <1435592237-17924-2-git-send-email-eric.auger@linaro.org> <011f01d0b498$6a17aeb0$3e470c10$@samsung.com> <5596503E.6040902@arm.com> <00fd01d0b7b6$f6cf3550$e46d9ff0$@samsung.com> <559A3C9C.6050302@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <559A3C9C.6050302@arm.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1982 Lines: 42 On Mon, Jul 06, 2015 at 09:30:20AM +0100, Andre Przywara wrote: > Hi Pavel, > > On 06/07/15 07:42, Pavel Fedin wrote: > > Hello! > > > >> I like this approach, but it runs into problems: > >> As you read above the current documentation says that the flags field > >> must be zero and the current KVM_SET_GSI_ROUTING handler bails out if it > >> isn't. So userland would need to know whether it's safe to set that > >> field. > > > > This problem does not exist because: > > a) Older platforms do not need this flag, so they expect to get zero. > > b) ARM64 + GICv3 platform cannot work without this flag. > > > > This is perfectly OK combination IMO. Userland just knows, whether it needs to supply device ID or > > not. For example, my modified qemu now has kvm_msi_flags global variable which defaults to 0. ITS > > code, then, if activated, changes it to KVM_MSI_VALID_DEVID, and qemu starts supplying device IDs to > > the related calls. > > Well, I had this solution before in kvmtool: If ARM && ITS then set the > flag. But I wasn't really happy with this, as the IRQ routing, setup and > injection code is rather architecture agnostic (implementing the generic > KVM interface), so spraying in some architecture hacks sounded not very > elegant. > Also as the flag describes a rather generic feature (provide an unique > device ID), I'd rather avoid to make this an ARM hack. > > That being said this is not a show stopper for me, so if the others are > happy with this, I will go down your road. > There must be some way for userspace to discover if it's valid to set the flag or not; either through a well-defined error-code probing mechanism for KVM_SET_GSI_ROUTING or through advertising a capability. -Christoffer -- 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/