[PATCH 8/9] vpci/header: Reset the command register when adding devices

[Oleksandr Andrushchenko <andr2000@gmail.com>]

From: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>

Reset the command register when passing through a PCI device:
it is possible that when passing through a PCI device its memory
decoding bits in the command register are already set. Thus, a
guest OS may not write to the command register to update memory
decoding, so guest mappings (guest's view of the BARs) are
left not updated.

Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
---
 xen/drivers/vpci/header.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/xen/drivers/vpci/header.c b/xen/drivers/vpci/header.c
index 7416ef1e1e06..dac973368b1e 100644
--- a/xen/drivers/vpci/header.c
+++ b/xen/drivers/vpci/header.c
@@ -811,6 +811,16 @@ int vpci_bar_add_handlers(const struct domain *d, struct pci_dev *pdev)
         gprintk(XENLOG_ERR,
             "%pp: failed to add BAR handlers for dom%d\n", &pdev->sbdf,
             d->domain_id);
+
+    /*
+     * Reset the command register: it is possible that when passing
+     * through a PCI device its memory decoding bits in the command
+     * register are already set. Thus, a guest OS may not write to the
+     * command register to update memory decoding, so guest mappings
+     * (guest's view of the BARs) are left not updated.
+     */
+    pci_conf_write16(pdev->sbdf, PCI_COMMAND, 0);
+
     return rc;
 }
 
-- 
2.25.1