[PATCH 5.10 011/306] PCI/MSI: Skip masking MSI-X on Xen PV

[Greg Kroah-Hartman]

From: Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>

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@xxxxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Acked-by: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Link: https://lore.kernel.org/r/20210826170342.135172-1-marmarek@xxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 drivers/pci/msi.c |    3 +++
 1 file changed, 3 insertions(+)

--- a/drivers/pci/msi.c
+++ b/drivers/pci/msi.c
@@ -783,6 +783,9 @@ 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);
 }