Re: virtio capabilities

[Alexey Kardashevskiy]

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




> 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