From 523184972b282cd9ca17a76f6ca4742394856818 Mon Sep 17 00:00:00 2001
From: Alex Williamson <alex.williamson@redhat.com>
Date: Mon, 2 Oct 2017 12:39:09 -0600
Subject: [PATCH] vfio/pci: Virtualize Maximum Payload Size
Git-commit: 523184972b282cd9ca17a76f6ca4742394856818
Patch-mainline: v4.15-rc1
References: bsc#1051510
With virtual PCI-Express chipsets, we now see userspace/guest drivers
trying to match the physical MPS setting to a virtual downstream port.
Of course a lone physical device surrounded by virtual interconnects
cannot make a correct decision for a proper MPS setting. Instead,
let's virtualize the MPS control register so that writes through to
hardware are disallowed. Userspace drivers like QEMU assume they can
write anything to the device and we'll filter out anything dangerous.
Since mismatched MPS can lead to AER and other faults, let's add it
to the kernel side rather than relying on userspace virtualization to
handle it.
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Acked-by: Takashi Iwai <tiwai@suse.de>
---
drivers/vfio/pci/vfio_pci_config.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/drivers/vfio/pci/vfio_pci_config.c b/drivers/vfio/pci/vfio_pci_config.c
index 5628fe114347..91335e6de88a 100644
--- a/drivers/vfio/pci/vfio_pci_config.c
+++ b/drivers/vfio/pci/vfio_pci_config.c
@@ -849,11 +849,13 @@ static int __init init_pci_cap_exp_perm(struct perm_bits *perm)
/*
* Allow writes to device control fields, except devctl_phantom,
- * which could confuse IOMMU, and the ARI bit in devctl2, which
+ * which could confuse IOMMU, MPS, which can break communication
+ * with other physical devices, and the ARI bit in devctl2, which
* is set at probe time. FLR gets virtualized via our writefn.
*/
p_setw(perm, PCI_EXP_DEVCTL,
- PCI_EXP_DEVCTL_BCR_FLR, ~PCI_EXP_DEVCTL_PHANTOM);
+ PCI_EXP_DEVCTL_BCR_FLR | PCI_EXP_DEVCTL_PAYLOAD,
+ ~PCI_EXP_DEVCTL_PHANTOM);
p_setw(perm, PCI_EXP_DEVCTL2, NO_VIRT, ~PCI_EXP_DEVCTL2_ARI);
return 0;
}
--
2.18.0