linux-kernel - Re: [PATCH] xen: do not re-use pirq number cached in pci device msi msg data

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Message-ID: <20170222142810.GA28359@bhelgaas-glaptop.roam.corp.google.com>
Date:   Wed, 22 Feb 2017 08:28:10 -0600
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Boris Ostrovsky <boris.ostrovsky@...cle.com>
Cc:     Juergen Gross <jgross@...e.com>, Dan Streetman <ddstreet@...e.org>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Dan Streetman <dan.streetman@...onical.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        xen-devel@...ts.xenproject.org,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-pci@...r.kernel.org
Subject: Re: [PATCH] xen: do not re-use pirq number cached in pci device msi
 msg data

On Tue, Feb 21, 2017 at 10:58:39AM -0500, Boris Ostrovsky wrote:
> On 02/21/2017 10:45 AM, Juergen Gross wrote:
> > On 21/02/17 16:31, Dan Streetman wrote:
> >> On Fri, Jan 13, 2017 at 5:30 PM, Konrad Rzeszutek Wilk
> >> <konrad.wilk@...cle.com> wrote:
> >>> On Fri, Jan 13, 2017 at 03:07:51PM -0500, Dan Streetman wrote:
> >>>> Revert the main part of commit:
> >>>> af42b8d12f8a ("xen: fix MSI setup and teardown for PV on HVM guests")
> >>>>
> >>>> That commit introduced reading the pci device's msi message data to see
> >>>> if a pirq was previously configured for the device's msi/msix, and re-use
> >>>> that pirq.  At the time, that was the correct behavior.  However, a
> >>>> later change to Qemu caused it to call into the Xen hypervisor to unmap
> >>>> all pirqs for a pci device, when the pci device disables its MSI/MSIX
> >>>> vectors; specifically the Qemu commit:
> >>>> c976437c7dba9c7444fb41df45468968aaa326ad
> >>>> ("qemu-xen: free all the pirqs for msi/msix when driver unload")
> >>>>
> >>>> Once Qemu added this pirq unmapping, it was no longer correct for the
> >>>> kernel to re-use the pirq number cached in the pci device msi message
> >>>> data.  All Qemu releases since 2.1.0 contain the patch that unmaps the
> >>>> pirqs when the pci device disables its MSI/MSIX vectors.
> >>>>
> >>>> This bug is causing failures to initialize multiple NVMe controllers
> >>>> under Xen, because the NVMe driver sets up a single MSIX vector for
> >>>> each controller (concurrently), and then after using that to talk to
> >>>> the controller for some configuration data, it disables the single MSIX
> >>>> vector and re-configures all the MSIX vectors it needs.  So the MSIX
> >>>> setup code tries to re-use the cached pirq from the first vector
> >>>> for each controller, but the hypervisor has already given away that
> >>>> pirq to another controller, and its initialization fails.
> >>>>
> >>>> This is discussed in more detail at:
> >>>> https://lists.xen.org/archives/html/xen-devel/2017-01/msg00447.html
> >>>>
> >>>> Fixes: af42b8d12f8a ("xen: fix MSI setup and teardown for PV on HVM guests")
> >>>> Signed-off-by: Dan Streetman <dan.streetman@...onical.com>
> >>> Acked-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
> >> This doesn't seem to be applied yet, is it still waiting on another
> >> ack?  Or maybe I'm looking at the wrong git tree...
> > Am I wrong or shouldn't this go through the PCI tree? Konrad?
> 
> Konrad is away this week but since pull request for Xen tree just went
> out we should probably wait until rc1 anyway (unless something big comes
> up before that).

I assume this should go via the Xen or x86 tree, since that's how most
arch/x86/pci/xen.c patches have been handled, including af42b8d12f8a.
If you think otherwise, let me know.