Re: [PATCH v2] kvm: Disable MSI/MSI-X in assigned device reset path

[Alex Williamson <alex.williamson@redhat.com>]

On Mon, 2012-04-16 at 18:06 +0300, Michael S. Tsirkin wrote:
> On Mon, Apr 16, 2012 at 08:03:17AM -0600, Alex Williamson wrote:
> > The discussion on this patch seems to have fizzled, with no clear short
> > term solution.
> 
> I think we are in concensus, it's just that there are
> multiple bugs still left to fix.
> 
> First, we need to prevent guest from touching command
> register except for the bus master bit. Something like
> the below? Compiled only.
> 
> device-assignment: don't touch pci command register
> 
> 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.
> 
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> 
> ---
> diff --git a/hw/device-assignment.c b/hw/device-assignment.c
> index 89823f1..9ebce49 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 +609,8 @@ 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;
>  
>      dev->region_number = r;
>      return 0;
> @@ -782,14 +777,6 @@ 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;

This doesn't look right ^^^, we'll never make use of host side INTx
disable support that way.  Thanks,

Alex

> -
> -        /* hide host-side INTx masking from the guest */
> -        dev->emulate_config_read[PCI_COMMAND + 1] |=
> -            PCI_COMMAND_INTX_DISABLE >> 8;
> -    }
>  
>      r = kvm_assign_pci_device(kvm_state, &assigned_dev_data);
>      if (r < 0) {
> @@ -1631,10 +1618,10 @@ 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 +1645,6 @@ 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);