From mboxrd@z Thu Jan 1 00:00:00 1970 Received: with ECARTIS (v1.0.0; list linux-mips); Fri, 04 Jul 2014 11:53:46 +0200 (CEST) Received: from mx1.redhat.com ([209.132.183.28]:61618 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by eddie.linux-mips.org with ESMTP id S6816005AbaGDJxnt1U9s (ORCPT ); Fri, 4 Jul 2014 11:53:43 +0200 Received: from int-mx14.intmail.prod.int.phx2.redhat.com (int-mx14.intmail.prod.int.phx2.redhat.com [10.5.11.27]) by mx1.redhat.com (8.14.4/8.14.4) with ESMTP id s649rZDT019439 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Fri, 4 Jul 2014 05:53:35 -0400 Received: from dhcp-26-207.brq.redhat.com (dhcp-26-192.brq.redhat.com [10.34.26.192]) by int-mx14.intmail.prod.int.phx2.redhat.com (8.14.4/8.14.4) with ESMTP id s649rU3i013233 (version=TLSv1/SSLv3 cipher=AES256-SHA bits=256 verify=NO); Fri, 4 Jul 2014 05:53:32 -0400 Date: Fri, 4 Jul 2014 11:54:34 +0200 From: Alexander Gordeev To: David Laight Cc: "'Bjorn Helgaas'" , "linux-mips@linux-mips.org" , "linux-s390@vger.kernel.org" , "linux-pci@vger.kernel.org" , "x86@kernel.org" , "linux-doc@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "linux-ide@vger.kernel.org" , "iommu@lists.linux-foundation.org" , "xen-devel@lists.xenproject.org" , "linuxppc-dev@lists.ozlabs.org" Subject: Re: [PATCH 1/3] PCI/MSI: Add pci_enable_msi_partial() Message-ID: <20140704095434.GC12247@dhcp-26-207.brq.redhat.com> References: <4fef62a2e647a7c38e9f2a1ea4244b3506a85e2b.1402405331.git.agordeev@redhat.com> <20140702202201.GA28852@google.com> <063D6719AE5E284EB5DD2968C1650D6D1726BF4E@AcuExch.aculab.com> <20140704085816.GB12247@dhcp-26-207.brq.redhat.com> <063D6719AE5E284EB5DD2968C1650D6D1726C717@AcuExch.aculab.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <063D6719AE5E284EB5DD2968C1650D6D1726C717@AcuExch.aculab.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-Scanned-By: MIMEDefang 2.68 on 10.5.11.27 Return-Path: X-Envelope-To: <"|/home/ecartis/ecartis -s linux-mips"> (uid 0) X-Orcpt: rfc822;linux-mips@linux-mips.org Original-Recipient: rfc822;linux-mips@linux-mips.org X-archive-position: 41021 X-ecartis-version: Ecartis v1.0.0 Sender: linux-mips-bounce@linux-mips.org Errors-to: linux-mips-bounce@linux-mips.org X-original-sender: agordeev@redhat.com Precedence: bulk List-help: List-unsubscribe: List-software: Ecartis version 1.0.0 List-Id: linux-mips X-List-ID: linux-mips List-subscribe: List-owner: List-post: List-archive: X-list: linux-mips On Fri, Jul 04, 2014 at 09:11:50AM +0000, David Laight wrote: > > I might be missing something, but we are talking of MSI address space > > here, aren't we? I am not getting how we could end up with a 'write' > > to a random kernel location when a unclaimed MSI vector sent. We could > > only expect a spurious interrupt at worst, which is handled and reported. > > > > Anyway, as I described in my reply to Bjorn, this is not a concern IMO. > > I'm thinking of the following - which might be MSI-X ? > 1) Hardware requests some interrupts and tells the host the BAR (and offset) > where the 'vectors' should be written. > 2) To raise an interrupt the hardware uses the 'vector' as the address > of a normal PCIe write cycle. > > So if the hardware requests 4 interrupts, but the driver (believing it > will only use 3) only write 3 vectors, and then the hardware uses the > 4th vector it can write to a random location. > > Debugging that would be hard! MSI base address is kind of hardcoded for a platform. A combination of MSI base address, PCI function number and MSI vector makes a PCI host to raise interrupt on a CPU. I might be inaccurate in details, but the scenario you described is impossible AFAICT. > David > > > -- Regards, Alexander Gordeev agordeev@redhat.com