pcie: check that slt ctrl changed before deleting

During boot, linux would sometimes overwrites control of a powered off
slot before powering it on. Unfortunately QEMU interprets that as a
power off request and ejects the device.

For example:

/x86_64-softmmu/qemu-system-x86_64 -enable-kvm -S -machine q35  \
    -device pcie-root-port,id=pcie_root_port_0,slot=2,chassis=2,addr=0x2,bus=pcie.0 \
    -monitor stdio disk.qcow2
(qemu)device_add virtio-balloon-pci,id=balloon,bus=pcie_root_port_0
(qemu)cont

Balloon is deleted during guest boot.

To fix, save control beforehand and check that power
or led state actually change before ejecting.

Note: this is more a hack than a solution, ideally we'd
find a better way to detect ejects, or move away
from ejects completely and instead monitor whether
it's safe to delete device due to e.g. its power state.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Marcel Apfelbaum <marcel.apfelbaum@gmail.com>
Reviewed-by: Igor Mammedov <imammedo@redhat.com>
Tested-by: Igor Mammedov <imammedo@redhat.com>

1 files changed, 4 insertions, 1 deletions

diff --git a/hw/pci-bridge/xio3130_downstream.c b/hw/pci-bridge/xio3130_downstream.c
index 264e37d6a6..899b0fd6c9 100644
--- a/hw/pci-bridge/xio3130_downstream.c
+++ b/hw/pci-bridge/xio3130_downstream.c
@@ -41,9 +41,12 @@
 static void xio3130_downstream_write_config(PCIDevice *d, uint32_t address,
                                          uint32_t val, int len)
 {
+    uint16_t slt_ctl, slt_sta;
+
+    pcie_cap_slot_get(d, &slt_sta, &slt_ctl);
     pci_bridge_write_config(d, address, val, len);
     pcie_cap_flr_write_config(d, address, val, len);
-    pcie_cap_slot_write_config(d, address, val, len);
+    pcie_cap_slot_write_config(d, slt_ctl, slt_sta, address, val, len);
     pcie_aer_write_config(d, address, val, len);
 }