Re: virtio capabilities

[Michael S. Tsirkin]

On Fri, Dec 13, 2019 at 07:29:40PM +1100, Alexey Kardashevskiy wrote:
> 
> 
> On 13/12/2019 18:24, Michael S. Tsirkin wrote:
> > 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
> 
> 
> Is there an easy way to tell if it is this "cf8/cfc" case?
> 
> I have these bars, is any of them related to cf8/cfc? Thanks,
> 
> root@le-dbg:~# (qemu) info mtree -f
> FlatView #0
>  AS "memory", root: system
>  AS "cpu-memory-0", root: system
>  Root memory region: system
>   0000000000000000-00000000ffffffff (prio 0, ram): ppc_spapr.ram kvm
>   0000200080000000-000020008000002f (prio 0, i/o): msix-table
>   0000200080000800-0000200080000807 (prio 0, i/o): msix-pba
>   0000210000000000-0000210000000fff (prio 0, i/o): virtio-pci-common
>   0000210000001000-0000210000001fff (prio 0, i/o): virtio-pci-isr
>   0000210000002000-0000210000002fff (prio 0, i/o): virtio-pci-device
>   0000210000003000-0000210000003fff (prio 0, i/o): virtio-pci-notify
> 


No, you want stuff in hw/ppc/spapr_pci.c

> 
> 
> > 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
> > 
> 
> -- 
> Alexey