From 247ab79234631b66283c47029eb895a8e3663e70 Mon Sep 17 00:00:00 2001 From: Konrad Rzeszutek Wilk Date: Fri, 27 Mar 2015 13:31:11 -0400 Subject: [PATCH 1/2] xen/pciback: Don't disable PCI_COMMAND on PCI device reset. There is no need for this at all. Worst it means that if the guest tries to write to BARs it could lead (on certain platforms) to PCI SERR errors. Please note that with af6fc858a35b90e89ea7a7ee58e66628c55c776b "xen-pciback: limit guest control of command register" a guest is still allowed to enable those control bits (safely), but is not allowed to disable them and that therefore a well behaved frontend which enables things before using them will still function correctly. This is done via an write to the configuration register 0x4 which triggers on the backend side: command_write \- pci_enable_device \- pci_enable_device_flags \- do_pci_enable_device \- pcibios_enable_device \-pci_enable_resourcess [which enables the PCI_COMMAND_MEMORY|PCI_COMMAND_IO] However guests (and drivers) which don't do this could cause problems, including the security issues which XSA-120 sought to address. Reported-by: Jan Beulich Signed-off-by: Konrad Rzeszutek Wilk --- drivers/xen/xen-pciback/pciback_ops.c | 2 -- 1 file changed, 2 deletions(-) diff --git a/drivers/xen/xen-pciback/pciback_ops.c b/drivers/xen/xen-pciback/pciback_ops.c index c4a0666..26e6513 100644 --- a/drivers/xen/xen-pciback/pciback_ops.c +++ b/drivers/xen/xen-pciback/pciback_ops.c @@ -119,8 +119,6 @@ void xen_pcibk_reset_device(struct pci_dev *dev) if (pci_is_enabled(dev)) pci_disable_device(dev); - pci_write_config_word(dev, PCI_COMMAND, 0); - dev->is_busmaster = 0; } else { pci_read_config_word(dev, PCI_COMMAND, &cmd); -- 2.1.0