Hi Alex,
On 12/02/2018 03:29 AM, Alex Williamson wrote:
> On Sat, 1 Dec 2018 10:52:21 -0800 (PST)
> Dongli Zhang <dongli.zh...@oracle.com> wrote:
>
>> Hi,
>>
>> I obtained below error when assigning an intel 760p 128GB nvme to guest via
>> vfio on my desktop:
>>
>> qemu-system-x86_64: -device vfio-pci,host=0000:01:00.0: vfio 0000:01:00.0:
>> failed to add PCI capability 0x11[0x50]@0xb0: table & pba overlap, or they
>> don't fit in BARs, or don't align
>>
>>
>> This is because the msix table is overlapping with pba. According to below
>> 'lspci -vv' from host, the distance between msix table offset and pba offset
>> is
>> only 0x100, although there are 22 entries supported (22 entries need 0x160).
>> Looks qemu supports at most 0x800.
>>
>> # sudo lspci -vv
>> ... ...
>> 01:00.0 Non-Volatile memory controller: Intel Corporation Device f1a6 (rev
>> 03) (prog-if 02 [NVM Express])
>> Subsystem: Intel Corporation Device 390b
>> ... ...
>> Capabilities: [b0] MSI-X: Enable- Count=22 Masked-
>> Vector table: BAR=0 offset=00002000
>> PBA: BAR=0 offset=00002100
>>
>>
>>
>> A patch below could workaround the issue and passthrough nvme successfully.
>>
>> diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c
>> index 5c7bd96..54fc25e 100644
>> --- a/hw/vfio/pci.c
>> +++ b/hw/vfio/pci.c
>> @@ -1510,6 +1510,11 @@ static void vfio_msix_early_setup(VFIOPCIDevice
>> *vdev, Error **errp)
>> msix->pba_offset = pba & ~PCI_MSIX_FLAGS_BIRMASK;
>> msix->entries = (ctrl & PCI_MSIX_FLAGS_QSIZE) + 1;
>>
>> + if (msix->table_bar == msix->pba_bar &&
>> + msix->table_offset + msix->entries * PCI_MSIX_ENTRY_SIZE >
>> msix->pba_offset) {
>> + msix->entries = (msix->pba_offset - msix->table_offset) /
>> PCI_MSIX_ENTRY_SIZE;
>> + }
>> +
>> /*
>> * Test the size of the pba_offset variable and catch if it extends
>> outside
>> * of the specified BAR. If it is the case, we need to apply a hardware
>>
>>
>> Would you please help confirm if this can be regarded as bug in qemu, or
>> issue
>> with nvme hardware? Should we fix thin in qemu, or we should never use such
>> buggy
>> hardware with vfio?
>
> It's a hardware bug, is there perhaps a firmware update for the device
> that resolves it? It's curious that a vector table size of 0x100 gives
> us 16 entries and 22 in hex is 0x16 (table size would be reported as
> 0x15 for the N-1 algorithm). I wonder if there's a hex vs decimal
> mismatch going on. We don't really know if the workaround above is
> correct, are there really 16 entries or maybe does the PBA actually
> start at a different offset? We wouldn't want to generically assume
> one or the other. I think we need Intel to tell us in which way their
> hardware is broken and whether it can or is already fixed in a firmware
> update. Thanks,
Thank you very much for the confirmation.
Just realized looks this would make trouble to my desktop as well when 17
vectors are used.
I will report to intel and confirm how this can happen and if there is any
firmware update available for this issue.
Dongli Zhang
