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

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From	Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH] xen: do not re-use pirq number cached in pci device msi msg data
Date	Fri, 13 Jan 2017 23:40:02 +0100
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X-Original-Cc	Stefano Stabellini <sstabellini@kernel.org>, jgross@suse.com, Boris Ostrovsky <boris.ostrovsky@oracle.com>, Dan Streetman <dan.streetman@canonical.com>, Bjorn Helgaas <bhelgaas@google.com>, xen-devel@lists.xenproject.org, linux-kernel <linux-kernel@vger.kernel.org>, linux-pci@vger.kernel.org
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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@canonical.com>

Acked-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

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[PATCH] xen: do not re-use pirq number cached in pci device msi msg data Dan Streetman <ddstreet@ieee.org> - 2017-01-13 21:10 +0100
  Re: [PATCH] xen: do not re-use pirq number cached in pci device msi  msg data Stefano Stabellini <sstabellini@kernel.org> - 2017-01-13 22:00 +0100
  Re: [PATCH] xen: do not re-use pirq number cached in pci device msi  msg data Boris Ostrovsky <boris.ostrovsky@oracle.com> - 2017-01-13 22:50 +0100
  Re: [PATCH] xen: do not re-use pirq number cached in pci device msi  msg data Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> - 2017-01-13 23:40 +0100

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