On Fri, Dec 13, 2019 at 05:05:05PM +1100, Alexey Kardashevskiy wrote: > 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,
Depends on the platform. E.g. on x86, when using cf8/cfc pair, if guest doesn't have a lock around programming the pair of registers, then one access can conflict with another one. When using express it's MMIO so shouldn't be a problem. > > [ 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