From 5b6471fc72a42e6110adca54f46fd2c287dc49d4 Mon Sep 17 00:00:00 2001 From: Simon Richter Date: Sun, 8 Mar 2026 02:35:37 +0900 Subject: [PATCH] PCI/VGA: Fail pci_set_vga_state() if VGA decoding not supported PCI bridges are allowed to refuse activating VGA decoding, by simply ignoring attempts to set the bit that enables it, so after setting the bit, read it back to verify. One example of such a bridge is the root bridge in IBM PowerNV, but this is also useful for GPU passthrough into virtual machines, where it is difficult to set up routing for legacy IO through IOMMU. Signed-off-by: Simon Richter [bhelgaas: subject, add comment about VGA Enable writability] Signed-off-by: Bjorn Helgaas Link: https://patch.msgid.link/20260307173538.763188-5-Simon.Richter@hogyros.de --- drivers/pci/pci.c | 12 ++++++++++++ 1 file changed, 12 insertions(+) diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c index 8479c2e1f74f1..52eb3ef0f487c 100644 --- a/drivers/pci/pci.c +++ b/drivers/pci/pci.c @@ -6197,6 +6197,18 @@ int pci_set_vga_state(struct pci_dev *dev, bool decode, cmd &= ~PCI_BRIDGE_CTL_VGA; pci_write_config_word(bridge, PCI_BRIDGE_CONTROL, cmd); + + + /* + * VGA Enable may not be writable if bridge doesn't + * support it. + */ + if (decode) { + pci_read_config_word(bridge, PCI_BRIDGE_CONTROL, + &cmd); + if (!(cmd & PCI_BRIDGE_CTL_VGA)) + return -EIO; + } } bus = bus->parent; } -- 2.47.3