[PATCH v4 09/11] 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>
---
Since v1:
 - do not write 0 to the command register, but respect host settings.
---
 xen/drivers/vpci/header.c | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/xen/drivers/vpci/header.c b/xen/drivers/vpci/header.c
index 64cfc268c341..680319b3a63f 100644
--- a/xen/drivers/vpci/header.c
+++ b/xen/drivers/vpci/header.c
@@ -459,8 +459,7 @@ static void cmd_write(const struct pci_dev *pdev, unsigned int reg,
         pci_conf_write16(pdev->sbdf, reg, cmd);
 }
 
-static void guest_cmd_write(const struct pci_dev *pdev, unsigned int reg,
-                            uint32_t cmd, void *data)
+static uint32_t emulate_cmd_reg(const struct pci_dev *pdev, uint32_t cmd)
 {
     /* TODO: Add proper emulation for all bits of the command register. */
 
@@ -472,7 +471,13 @@ static void guest_cmd_write(const struct pci_dev *pdev, unsigned int reg,
     }
 #endif
 
-    cmd_write(pdev, reg, cmd, data);
+    return cmd;
+}
+
+static void guest_cmd_write(const struct pci_dev *pdev, unsigned int reg,
+                            uint32_t cmd, void *data)
+{
+    cmd_write(pdev, reg, emulate_cmd_reg(pdev, cmd), data);
 }
 
 static void bar_write(const struct pci_dev *pdev, unsigned int reg,
@@ -646,6 +651,10 @@ static int init_bars(struct pci_dev *pdev)
         return -EOPNOTSUPP;
     }
 
+    /* Reset the command register for the guest. */
+    if ( !is_hwdom )
+        pci_conf_write16(pdev->sbdf, PCI_COMMAND, emulate_cmd_reg(pdev, 0));
+
     /* Setup a handler for the command register. */
     rc = vpci_add_register(pdev->vpci, vpci_hw_read16,
                            is_hwdom ? cmd_write : guest_cmd_write,
-- 
2.25.1