virtio capabilities

[Alexey Kardashevskiy]

Hi!

I am having an issue with capabilities (hopefully the chunk formatting
won't break).

The problem is that when virtio_pci_find_capability() reads
pci_find_capability(dev, PCI_CAP_ID_VNDR), 0 is returned; if repeated,
it returns a valid number (0x84). Timing seems to matter. pci_cfg_read
trace shows that that first time read does not reach QEMU but others do
reach QEMU and return what is expected.

How to debug this, any quick ideas? The config space is not a MMIO BAR
or KVM memory slot or anything like this, right? :) Thanks,


[    3.489492] ___K___ (0) virtio_pci_modern_probe 642
[    3.489697] ___K___ (0) virtio_pci_find_capability 492: FIND a cap
[    3.490070] ___K___ (0) virtio_pci_find_capability 494: cap is at 0
[    3.490335] ___K___ (0) virtio_pci_find_capability 492: FIND a cap
10909@1576216763.643271:pci_cfg_read virtio-net-pci 00:0 @0x6 -> 0x10
10909@1576216763.643431:pci_cfg_read virtio-net-pci 00:0 @0x34 -> 0x98
10909@1576216763.643591:pci_cfg_read virtio-net-pci 00:0 @0x98 -> 0x8411
10909@1576216763.643747:pci_cfg_read virtio-net-pci 00:0 @0x84 -> 0x7009
[    3.491264] ___K___ (0) virtio_pci_find_capability 494: cap is at 132
10909@1576216763.644140:pci_cfg_read virtio-net-pci 00:0 @0x87 -> 0x5
10909@1576216763.644287:pci_cfg_read virtio-net-pci 00:0 @0x88 -> 0x0
[    3.491803] ___K___ (0) virtio_pci_find_capability 506: 5 0
10909@1576216763.644632:pci_cfg_read virtio-net-pci 00:0 @0x85 -> 0x70
10909@1576216763.644786:pci_cfg_read virtio-net-pci 00:0 @0x70 -> 0x6009
10909@1576216763.644942:pci_cfg_read virtio-net-pci 00:0 @0x73 -> 0x2
10909@1576216763.645092:pci_cfg_read virtio-net-pci 00:0 @0x74 -> 0x4
[    3.492607] ___K___ (0) virtio_pci_find_capability 506: 2 4





diff --git a/drivers/virtio/virtio_pci_modern.c
b/drivers/virtio/virtio_pci_modern.c
index 7abcc50838b8..85b2a7ce96e9 100644
--- a/drivers/virtio/virtio_pci_modern.c
+++ b/drivers/virtio/virtio_pci_modern.c
@@ -486,9 +486,14 @@ static const struct virtio_config_ops
virtio_pci_config_ops = {
 static inline int virtio_pci_find_capability(struct pci_dev *dev, u8
cfg_type,
                                             u32 ioresource_types, int
*bars)
 {
-       int pos;
+       int pos = 0;// = pci_find_capability(dev, PCI_CAP_ID_VNDR);

-       for (pos = pci_find_capability(dev, PCI_CAP_ID_VNDR);
+       while (!pos) {
+               pr_err("___K___ (%u) %s %u: FIND a cap\n",
smp_processor_id(), __func__, __LINE__);
+               pos = pci_find_capability(dev, PCI_CAP_ID_VNDR);
+               pr_err("___K___ (%u) %s %u: cap is at %d\n",
smp_processor_id(), __func__, __LINE__, pos);
+       }
+       for (;
             pos > 0;
             pos = pci_find_next_capability(dev, pos, PCI_CAP_ID_VNDR)) {
                u8 type, bar;


-- 
Alexey