[PATCH] pci: avoid bridge feature re-probing on hotplug

From: Michael S. Tsirkin
Date: Mon Dec 10 2018 - 21:18:44 EST

commit 1f82de10d6 ("PCI/x86: don't assume prefetchable ranges are
64bit") added probing of bridge support for 64 bit memory
each time bridge is re-enumerated.

Unfortunately this probing is destructive if any device behind
the bridge is in use at this time.

There's no real need to re-probe the bridge features as the
regiters in question never change - detect that using
the memory flag being set and skip the probing.
Avoiding repeated calls to pci_bridge_check_ranges might be even nicer
would be a bigger patch and probably not appropriate on stable.

Reported-by: xuyandong <xuyandong2@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Cc: Yinghai Lu <yinghai@xxxxxxxxxx>
Cc: Jesse Barnes <jbarnes@xxxxxxxxxxxxxxxx>
Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>

This issue has been reported on upstream Linux and Centos.

drivers/pci/setup-bus.c | 7 +++++++
1 file changed, 7 insertions(+)

diff --git a/drivers/pci/setup-bus.c b/drivers/pci/setup-bus.c
index ed960436df5e..7ab42f76579e 100644
--- a/drivers/pci/setup-bus.c
+++ b/drivers/pci/setup-bus.c
@@ -741,6 +741,13 @@ static void pci_bridge_check_ranges(struct pci_bus *bus)
struct resource *b_res;

b_res = &bridge->resource[PCI_BRIDGE_RESOURCES];
+ /* Don't re-check after this was called once already:
+ * important since bridge might be in use.
+ */
+ if (b_res[1].flags & IORESOURCE_MEM)
+ return;
b_res[1].flags |= IORESOURCE_MEM;

pci_read_config_word(bridge, PCI_IO_BASE, &io);