From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756111AbbAHQP1 (ORCPT ); Thu, 8 Jan 2015 11:15:27 -0500 Received: from mail-ob0-f178.google.com ([209.85.214.178]:65117 "EHLO mail-ob0-f178.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754104AbbAHQPZ (ORCPT ); Thu, 8 Jan 2015 11:15:25 -0500 Date: Thu, 8 Jan 2015 09:15:21 -0700 From: Bjorn Helgaas To: Alex Williamson Cc: linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org, x86@kernel.org, tglx@linutronix.de, mingo@redhat.com, hpa@zytor.com, joro@8bytes.org, iommu@lists.linux-foundation.org Subject: Re: [PATCH 0/3] PCI/x86: Interface for testing multivector MSI support Message-ID: <20150108161521.GB6575@google.com> References: <20141121213752.31095.30735.stgit@gimli.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20141121213752.31095.30735.stgit@gimli.home> 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 On Fri, Nov 21, 2014 at 03:08:27PM -0700, Alex Williamson wrote: > I'd like to make vfio-pci capable of manipulating the device exposed > to the user such that if the host can only support a single MSI > vector then we hide the fact that the device itself may actually be > able to support more. When we virtualize PCI config space and > interrupt setup there's no PCI protocol for the device failing to > allocate the number of vectors that it said were available. If the > userspace driver is a guest operating system, it certainly doesn't > expect this to fail. I don't think we can ever guarantee that a > multi-vector request will succeed, but we can certainly guarantee > that it will fail if the platform doesn't support it. > > An example device is the Atheros AR93xxx running in a Windows 7 VM. > Both the device and the guest OS support multiple MSI vectors. With > interrupt remapping, such that the host supports multivector, the > device works well in the guest. With interrupt remapping disabled, > the device is far less reliable because of the mismatch in MSI > programming vs driver configuration and often fails. If vfio-pci > can test whether multiple vectors are supported, then we can make it > work reliably in both cases by adjusting the exposed MSI capability, > like in this patch that would follow this series: > > https://github.com/awilliam/linux-vfio/commit/9ace67515680 > > With this series, only x86 w/ interrupt remapping will advertise > support for multiple MSI vectors. In surveying the code, I couldn't > find any other archs that allowed it, but I'll take corrections if > that's untrue. Thanks, Per Thomas' comments and your possible workaround if we don't have pci_msi_supported(), I'm going to ignore these for now. Let me know if you disagree. Bjorn > --- > > Alex Williamson (3): > PCI: Extend and export pci_msi_supported() for multivector MSI > PCI/x86: Add arch_supports_multivector_msi() hook > PCI/MSI: Initial hook for archs to declare multivector MSI support > > > arch/x86/include/asm/x86_init.h | 1 + > arch/x86/kernel/x86_init.c | 6 ++++++ > drivers/iommu/irq_remapping.c | 6 ++++++ > drivers/pci/msi.c | 20 +++++++++++++++++--- > include/linux/msi.h | 1 + > include/linux/pci.h | 3 +++ > 6 files changed, 34 insertions(+), 3 deletions(-)