[PATCHv2] device-assignment: don't touch real command register

["Michael S. Tsirkin" <mst@redhat.com>]

Real command register is under kernel control:
it includes bits for triggering SERR, marking
BARs as invalid and such which are under host
kernel control. Don't touch any except bus master
which is ok to put under guest control and intx
mask which kvm interrupt sharing machinery
explicitly allows.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

---
Compiled only, don't have a setup for assignment
testing ATM. Is anyone interested enough to test
and report?

Changes from v1:
- fix intx mask handling

 hw/device-assignment.c |   24 ++++++++----------------
 1 files changed, 8 insertions(+), 16 deletions(-)

diff --git a/hw/device-assignment.c b/hw/device-assignment.c
index 89823f1..6cdcc17 100644
--- a/hw/device-assignment.c
+++ b/hw/device-assignment.c
@@ -501,7 +501,6 @@ static int get_real_device(AssignedDevice *pci_dev, uint16_t r_seg,
     FILE *f;
     unsigned long long start, end, size, flags;
     uint16_t id;
-    struct stat statbuf;
     PCIRegion *rp;
     PCIDevRegions *dev = &pci_dev->real_device;
 
@@ -610,12 +609,9 @@ again:
     pci_dev->dev.config[2] = id & 0xff;
     pci_dev->dev.config[3] = (id & 0xff00) >> 8;
 
-    /* dealing with virtual function device */
-    snprintf(name, sizeof(name), "%sphysfn/", dir);
-    if (!stat(name, &statbuf)) {
-        /* always provide the written value on readout */
-        assigned_dev_emulate_config_read(pci_dev, PCI_COMMAND, 2);
-    }
+    /* Pass bus master writes to device. */
+    pci_dev->emulate_config_write[PCI_COMMAND] &= ~PCI_COMMAND_MASTER;
+    pci_dev->emulate_config_write[PCI_COMMAND + 1] &= ~(PCI_COMMAND_INTX_DISABLE >> 8);
 
     dev->region_number = r;
     return 0;
@@ -782,13 +778,10 @@ static int assign_device(AssignedDevice *dev)
                 "cause host memory corruption if the device issues DMA write "
                 "requests!\n");
     }
-    if (dev->features & ASSIGNED_DEVICE_SHARE_INTX_MASK &&
-        kvm_has_intx_set_mask()) {
-        assigned_dev_data.flags |= KVM_DEV_ASSIGN_PCI_2_3;
 
-        /* hide host-side INTx masking from the guest */
-        dev->emulate_config_read[PCI_COMMAND + 1] |=
-            PCI_COMMAND_INTX_DISABLE >> 8;
+    if (dev->features & ASSIGNED_DEVICE_SHARE_INTX_MASK &&
+	kvm_has_intx_set_mask()) {
+	    assigned_dev_data.flags |= KVM_DEV_ASSIGN_PCI_2_3;
     }
 
     r = kvm_assign_pci_device(kvm_state, &assigned_dev_data);
@@ -1631,10 +1624,10 @@ static void reset_assigned_device(DeviceState *dev)
     }
 
     /*
-     * When a 0 is written to the command register, the device is logically
+     * When a 0 is written to the bus master register, the device is logically
      * disconnected from the PCI bus. This avoids further DMA transfers.
      */
-    assigned_dev_pci_write_config(pci_dev, PCI_COMMAND, 0, 2);
+    assigned_dev_pci_write_config(pci_dev, PCI_COMMAND, 0, 1);
 }
 
 static int assigned_initfn(struct PCIDevice *pci_dev)
@@ -1658,7 +1651,6 @@ static int assigned_initfn(struct PCIDevice *pci_dev)
      * device initialization.
      */
     assigned_dev_emulate_config_read(dev, 0, PCI_CONFIG_SPACE_SIZE);
-    assigned_dev_direct_config_read(dev, PCI_COMMAND, 2);
     assigned_dev_direct_config_read(dev, PCI_STATUS, 2);
     assigned_dev_direct_config_read(dev, PCI_REVISION_ID, 1);
     assigned_dev_direct_config_read(dev, PCI_CLASS_PROG, 3);
-- 
1.7.9.111.gf3fb0