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    Subject[PATCH 4.19 122/293] PCI/MSI: Skip masking MSI-X on Xen PV
    Date
    From: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>

    commit 1a519dc7a73c977547d8b5108d98c6e769c89f4b upstream.

    When running as Xen PV guest, masking MSI-X is a responsibility of the
    hypervisor. The guest has no write access to the relevant BAR at all - when
    it tries to, it results in a crash like this:

    BUG: unable to handle page fault for address: ffffc9004069100c
    #PF: supervisor write access in kernel mode
    #PF: error_code(0x0003) - permissions violation
    RIP: e030:__pci_enable_msix_range.part.0+0x26b/0x5f0
    e1000e_set_interrupt_capability+0xbf/0xd0 [e1000e]
    e1000_probe+0x41f/0xdb0 [e1000e]
    local_pci_probe+0x42/0x80
    (...)

    The recently introduced function msix_mask_all() does not check the global
    variable pci_msi_ignore_mask which is set by XEN PV to bypass the masking
    of MSI[-X] interrupts.

    Add the check to make this function XEN PV compatible.

    Fixes: 7d5ec3d36123 ("PCI/MSI: Mask all unused MSI-X entries")
    Signed-off-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>
    Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
    Acked-by: Bjorn Helgaas <bhelgaas@google.com>
    Cc: stable@vger.kernel.org
    Link: https://lore.kernel.org/r/20210826170342.135172-1-marmarek@invisiblethingslab.com
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    drivers/pci/msi.c | 3 +++
    1 file changed, 3 insertions(+)

    --- a/drivers/pci/msi.c
    +++ b/drivers/pci/msi.c
    @@ -754,6 +754,9 @@ static void msix_mask_all(void __iomem *
    u32 ctrl = PCI_MSIX_ENTRY_CTRL_MASKBIT;
    int i;

    + if (pci_msi_ignore_mask)
    + return;
    +
    for (i = 0; i < tsize; i++, base += PCI_MSIX_ENTRY_SIZE)
    writel(ctrl, base + PCI_MSIX_ENTRY_VECTOR_CTRL);
    }

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