PCI: Probe bridge window attributes once at enumeration-time

mainline inclusion
from mainline-5.1
commit: <not-yet-available>
category: bugfix
bugzilla: 5473
CVE: NA

----------------------------------------

pci_bridge_check_ranges() determines whether a bridge supports the optional
I/O and prefetchable memory windows and sets the flag bits in the bridge
resources.  This could be done once during enumeration except that the
resource allocation code completely clears the flag bits, e.g., in the
pci_assign_unassigned_bridge_resources() path.

The problem was that in some cases pci_bridge_check_ranges() *changes* the
window registers to determine whether they're writable, and this may break
concurrent accesses to devices behind the bridge.

Add a new pci_read_bridge_windows() to determine whether a bridge supports
the optional windows, call it once during enumeration, remember the
results, and change pci_bridge_check_ranges() to set the flag bits based on
those remembered results.

Link: https://lore.kernel.org/linux-pci/1506151482-113560-1-git-send-email-wangzhou1@hisilicon.com
Link: https://lists.gnu.org/archive/html/qemu-devel/2018-12/msg02082.html


Reported-by: xuyandong <xuyandong2@huawei.com>
Cc: Sagi Grimberg <sagi@grimberg.me>
Cc: Ofer Hayut <ofer@lightbitslabs.com>
Cc: Roy Shterman <roys@lightbitslabs.com>
Cc: Keith Busch <keith.busch@intel.com>
Cc: Zhou Wang <wangzhou1@hisilicon.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Reviewed-by: Xiongfeng Wang <wangxiongfeng2@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>