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    Subject[PATCH 3.4 097/125] xen/pciback: Return error on XEN_PCI_OP_enable_msi when device has MSI or MSI-X enabled
    Date
    From: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

    3.4.113-rc1 review patch. If anyone has any objections, please let me know.

    ------------------


    commit 56441f3c8e5bd45aab10dd9f8c505dd4bec03b0d upstream.

    The guest sequence of:

    a) XEN_PCI_OP_enable_msi
    b) XEN_PCI_OP_enable_msi
    c) XEN_PCI_OP_disable_msi

    results in hitting an BUG_ON condition in the msi.c code.

    The MSI code uses an dev->msi_list to which it adds MSI entries.
    Under the above conditions an BUG_ON() can be hit. The device
    passed in the guest MUST have MSI capability.

    The a) adds the entry to the dev->msi_list and sets msi_enabled.
    The b) adds a second entry but adding in to SysFS fails (duplicate entry)
    and deletes all of the entries from msi_list and returns (with msi_enabled
    is still set). c) pci_disable_msi passes the msi_enabled checks and hits:

    BUG_ON(list_empty(dev_to_msi_list(&dev->dev)));

    and blows up.

    The patch adds a simple check in the XEN_PCI_OP_enable_msi to guard
    against that. The check for msix_enabled is not stricly neccessary.

    This is part of XSA-157.

    Reviewed-by: David Vrabel <david.vrabel@citrix.com>
    Reviewed-by: Jan Beulich <jbeulich@suse.com>
    Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
    Signed-off-by: Zefan Li <lizefan@huawei.com>
    ---
    drivers/xen/xen-pciback/pciback_ops.c | 7 ++++++-
    1 file changed, 6 insertions(+), 1 deletion(-)

    diff --git a/drivers/xen/xen-pciback/pciback_ops.c b/drivers/xen/xen-pciback/pciback_ops.c
    index a751a66..1ab998c 100644
    --- a/drivers/xen/xen-pciback/pciback_ops.c
    +++ b/drivers/xen/xen-pciback/pciback_ops.c
    @@ -143,7 +143,12 @@ int xen_pcibk_enable_msi(struct xen_pcibk_device *pdev,
    if (unlikely(verbose_request))
    printk(KERN_DEBUG DRV_NAME ": %s: enable MSI\n", pci_name(dev));

    - status = pci_enable_msi(dev);
    + if (dev->msi_enabled)
    + status = -EALREADY;
    + else if (dev->msix_enabled)
    + status = -ENXIO;
    + else
    + status = pci_enable_msi(dev);

    if (status) {
    pr_warn_ratelimited(DRV_NAME ": %s: error enabling MSI for guest %u: err %d\n",
    --
    1.9.1
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