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

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Date:   Fri, 13 Jan 2017 17:30:35 -0500
From:   Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:     Dan Streetman <ddstreet@...e.org>
Cc:     Stefano Stabellini <sstabellini@...nel.org>, jgross@...e.com,
        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 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>