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

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Fri, 13 Jan 2017, 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@xxxxxxxxxxxxx>

Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>


> ---
>  arch/x86/pci/xen.c | 23 +++++++----------------
>  1 file changed, 7 insertions(+), 16 deletions(-)
> 
> diff --git a/arch/x86/pci/xen.c b/arch/x86/pci/xen.c
> index bedfab9..a00a6c0 100644
> --- a/arch/x86/pci/xen.c
> +++ b/arch/x86/pci/xen.c
> @@ -234,23 +234,14 @@ static int xen_hvm_setup_msi_irqs(struct pci_dev *dev, 
> int nvec, int type)
>               return 1;
>  
>       for_each_pci_msi_entry(msidesc, dev) {
> -             __pci_read_msi_msg(msidesc, &msg);
> -             pirq = MSI_ADDR_EXT_DEST_ID(msg.address_hi) |
> -                     ((msg.address_lo >> MSI_ADDR_DEST_ID_SHIFT) & 0xff);
> -             if (msg.data != XEN_PIRQ_MSI_DATA ||
> -                 xen_irq_from_pirq(pirq) < 0) {
> -                     pirq = xen_allocate_pirq_msi(dev, msidesc);
> -                     if (pirq < 0) {
> -                             irq = -ENODEV;
> -                             goto error;
> -                     }
> -                     xen_msi_compose_msg(dev, pirq, &msg);
> -                     __pci_write_msi_msg(msidesc, &msg);
> -                     dev_dbg(&dev->dev, "xen: msi bound to pirq=%d\n", pirq);
> -             } else {
> -                     dev_dbg(&dev->dev,
> -                             "xen: msi already bound to pirq=%d\n", pirq);
> +             pirq = xen_allocate_pirq_msi(dev, msidesc);
> +             if (pirq < 0) {
> +                     irq = -ENODEV;
> +                     goto error;
>               }
> +             xen_msi_compose_msg(dev, pirq, &msg);
> +             __pci_write_msi_msg(msidesc, &msg);
> +             dev_dbg(&dev->dev, "xen: msi bound to pirq=%d\n", pirq);
>               irq = xen_bind_pirq_msi_to_irq(dev, msidesc, pirq,
>                                              (type == PCI_CAP_ID_MSI) ? nvec 
> : 1,
>                                              (type == PCI_CAP_ID_MSIX) ?
> -- 
> 2.9.3
> 

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