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

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Date:   Tue, 21 Feb 2017 16:45:20 +0100
From:   Juergen Gross <jgross@...e.com>
To:     Dan Streetman <ddstreet@...e.org>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Cc:     Stefano Stabellini <sstabellini@...nel.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        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 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?


Juergen