PCI/MSI: Skip masking MSI-X on Xen PV

stable inclusion
from linux-4.19.207
commit 34b23fc32c05f14fd21caa32544f3720e1527a8d

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

commit 1a519dc7 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: 7d5ec3d3 ("PCI/MSI: Mask all unused MSI-X entries")
Signed-off-by: NMarek Marczykowski-Górecki <marmarek@invisiblethingslab.com>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>
Acked-by: NBjorn Helgaas <bhelgaas@google.com>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20210826170342.135172-1-marmarek@invisiblethingslab.comSigned-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

drivers/pci/msi.c

@@ -765,6 +765,9 @@ static void msix_mask_all(void __iomem *base, int tsize)
 	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);
 }