Re: [Qemu-devel] [PATCH v6 4/7] hw/pci-bridge: disable hotplug in PXB

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

On Wed, Jun 17, 2015 at 02:45:02PM +0200, Laszlo Ersek wrote:
> OVMF downloads the ACPI linker/loader script from QEMU when the edk2 PCI
> Bus driver globally signals the firmware that PCI enumeration and resource
> allocation have completed. At this point QEMU regenerates the ACPI payload
> in an fw_cfg read callback, and this is when the PXB's _CRS gets
> populated.
> 
> Unfortunately, when this happens, the PCI_COMMAND_MEMORY bit is clear in
> the root bus's command register, *unlike* under SeaBIOS. The consequences
> unfold as follows:
> 
> - When build_crs() fetches dev->io_regions[i].addr, it is all-bits-one,
>   because pci_update_mappings() --> pci_bar_address() calculated it as
>   PCI_BAR_UNMAPPED, due to the PCI_COMMAND_MEMORY bit being clear.
> 
> - Consequently, the SHPC MMIO BAR (bar 0) of the bridge is not added to
>   the _CRS, *despite* having been programmed in PCI config space.
> 
> - Similarly, the SHPC MMIO BAR of the PXB is not removed from the main
>   root bus's DWordMemory descriptor.
> 
> - Guest OSes (Linux and Windows alike) notice the pre-programmed SHPC BAR
>   within the PXB's config space, and notice that it conflicts with the
>   main root bus's memory resource descriptors. Linux reports
> 
>   pci 0000:04:00.0: BAR 0: can't assign mem (size 0x100)
>   pci 0000:04:00.0: BAR 0: trying firmware assignment [mem
>                            0x88200000-0x882000ff 64bit]
>   pci 0000:04:00.0: BAR 0: [mem 0x88200000-0x882000ff 64bit] conflicts
>                            with PCI Bus 0000:00 [mem
>                            0x88200000-0xfebfffff]
> 
>   While Windows Server 2012 R2 reports
> 
>     https://technet.microsoft.com/en-us/library/cc732199%28v=ws.10%29.aspx
> 
>     This device cannot find enough free resources that it can use. If you
>     want to use this device, you will need to disable one of the other
>     devices on this system. (Code 12)
> 
> This issue was apparently encountered earlier, see the "hack" in:
> 
>   https://lists.nongnu.org/archive/html/qemu-devel/2015-01/msg02983.html
> 
> and the current hole-punching logic in build_crs() and build_ssdt() is
> probably supposed to remedy exactly that problem -- however, for OVMF they
> don't work, because at the end of the PCI enumeration and resource
> allocation, which cues the ACPI linker/loader client, the command register
> is clear.
> 
> The "hotplug" property of "pci-bridge", introduced in the previous
> patches, enables us to disable the standard hotplug controller cleanly,
> eliminating the SHPC bar and the conflict.
> 
> Cc: Michael S. Tsirkin <mst@redhat.com>
> Cc: Marcel Apfelbaum <marcel@redhat.com>
> Signed-off-by: Laszlo Ersek <lersek@redhat.com>
> ---
> 
> Notes:
>     v6:
>     - new in v6 (replaces "hw/pci-bridge: create interrupt-less,
>       hotplug-less bridge for PXB" from v5) [Michael]
> 
>  hw/pci-bridge/pci_expander_bridge.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/hw/pci-bridge/pci_expander_bridge.c b/hw/pci-bridge/pci_expander_bridge.c
> index ec2bb45..4398d98 100644
> --- a/hw/pci-bridge/pci_expander_bridge.c
> +++ b/hw/pci-bridge/pci_expander_bridge.c
> @@ -176,6 +176,7 @@ static int pxb_dev_initfn(PCIDevice *dev)
>      bds = qdev_create(BUS(bus), "pci-bridge");
>      bds->id = dev_name;
>      qdev_prop_set_uint8(bds, "chassis_nr", pxb->bus_nr);

BTW this is a bug: it will conflict with chassis_nr
on another bridge if user set it. Not related to this
patch of course.

> +    qdev_prop_set_bit(bds, "hotplug", false);
>  
>      PCI_HOST_BRIDGE(ds)->bus = bus;
>  
> -- 
> 1.8.3.1
>