[PATCH v2 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 | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/xen/drivers/vpci/header.c b/xen/drivers/vpci/header.c
index 99f9c37dfb00..b2829b9d206b 100644
--- a/xen/drivers/vpci/header.c
+++ b/xen/drivers/vpci/header.c
@@ -452,8 +452,7 @@ 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. */
 
@@ -468,14 +467,20 @@ static void guest_cmd_write(const struct pci_dev *pdev, unsigned int reg,
             cmd |= PCI_COMMAND_INTX_DISABLE;
         else
         {
-            uint16_t current_cmd = pci_conf_read16(pdev->sbdf, reg);
+            uint16_t current_cmd = pci_conf_read16(pdev->sbdf, PCI_COMMAND);
 
             if ( current_cmd & PCI_COMMAND_INTX_DISABLE )
                 cmd |= PCI_COMMAND_INTX_DISABLE;
         }
     }
 
-    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,
@@ -794,6 +799,10 @@ int vpci_bar_add_handlers(const struct domain *d, const struct pci_dev *pdev)
         gdprintk(XENLOG_ERR,
                  "%pp: failed to add BAR handlers for dom%pd: %d\n",
                  &pdev->sbdf, d, rc);
+
+    /* Reset the command register with respect to host settings. */
+    pci_conf_write16(pdev->sbdf, PCI_COMMAND, emulate_cmd_reg(pdev, 0));
+
     return rc;
 }
 
-- 
2.25.1