Re: PCIe device paththrough via vfio issue

[Alex Williamson <alex.williamson@redhat.com>]

On Mon, 13 Jan 2020 18:49:21 +0300
yurij <lnkgyv@gmail.com> wrote:

> Hello everybody!
> 
> I have a specific PCIe device (sorry, but I can't tell about what is it 
> and what it does) but PCI configuration space consists of 4 BARs (lspci 
> output brief):
> 
> lspci -s 84:00.00 -vvv
> 
> . . .
> Region 0: Memory at fa000000 (64-bit, non-prefetchable) [size=16M]
> 	Region 2: Memory at fb001000 (32-bit, non-prefetchable) [size=4K]
> 	Region 3: Memory at fb000000 (32-bit, non-prefetchable) [size=4K]
> 	Region 4: Memory at f9000000 (64-bit, non-prefetchable) [size=16M]
> . . .
> Kernel driver in use: vfio-pci
> . . .
> 
> BAR0 merged with BAR1, BAR4 merged with BAR5 so they are 64 bit width.
> 
> I put this PCIe device in virtual machine via vfio:
> 
> -device vfio-pci,host=84:00.0,id=hostdev0,bus=pci.6,addr=0x0
> 
> Virtual machine successfully boot. PCI configuration space in virtual 
> environment looks OK (lspci output brief):
> 
> lspci -s 06:00.0 -vvv
> 
> . . .
> Region 0: Memory at f8000000 (64-bit, non-prefetchable) [size=16M]
> 	Region 2: Memory at fa000000 (32-bit, non-prefetchable) [size=4K]
> 	Region 3: Memory at fa001000 (32-bit, non-prefetchable) [size=4K]
> 	Region 4: Memory at f9000000 (64-bit, non-prefetchable) [size=16M]
> . . .
> Kernel driver in use: custom_driver
> 
> BAR0 merged with BAR1 and BAR4 merged with BAR5 and so they are also 64 
> bit width.
> 
> The main problem in 4K HOLE in REGION 0 in virtual environment. So some 
> device features don't work.
> 
> I have enabled iommu trace in host system (trace_event=iommu) and 
> display all events (for i in $(find 
> /sys/kernel/debug/tracing/events/iommu/ -name enable);do echo 1 > $i; 
> done). I saw next events during virtual machine booting:
> 
> # cat /sys/kernel/debug/tracing/trace
> . . .
>         CPU 0/KVM-3046  [051] .... 63113.338894: map: IOMMU: 
> iova=0x00000000f8000000 paddr=0x00000000fa000000 size=24576
>         CPU 0/KVM-3046  [051] .... 63113.339177: map: IOMMU: 
> iova=0x00000000f8007000 paddr=0x00000000fa007000 size=16748544
>         CPU 0/KVM-3046  [051] .... 63113.339444: map: IOMMU: 
> iova=0x00000000fa000000 paddr=0x00000000fb001000 size=4096
>         CPU 0/KVM-3046  [051] .... 63113.339697: map: IOMMU: 
> iova=0x00000000fa001000 paddr=0x00000000fb000000 size=4096
>         CPU 0/KVM-3046  [051] .... 63113.340209: map: IOMMU: 
> iova=0x00000000f9000000 paddr=0x00000000f9000000 size=16777216
> . . .
> 
> I have enabled qemu trace(-trace events=/root/qemu/trace_events). Trace 
> file consists of the falling functions:
> vfio_region_mmap
> vfio_get_dev_region
> vfio_pci_size_rom
> vfio_pci_read_config
> vfio_pci_write_config
> vfio_iommu_map_notify
> vfio_listener_region_add_iommu
> vfio_listener_region_add_ram
> 
> Some important brief from qemu trace:
> . . .
> янв 13 18:17:24 VM qemu-system-x86_64[7131]: vfio_region_mmap Region 
> 0000:84:00.0 BAR 0 mmaps[0] [0x0 - 0xffffff]
> янв 13 18:17:24 VM qemu-system-x86_64[7131]: vfio_region_mmap Region 
> 0000:84:00.0 BAR 2 mmaps[0] [0x0 - 0xfff]
> янв 13 18:17:24 VM qemu-system-x86_64[7131]: vfio_region_mmap Region 
> 0000:84:00.0 BAR 3 mmaps[0] [0x0 - 0xfff]
> янв 13 18:17:24 VM qemu-system-x86_64[7131]: vfio_region_mmap Region 
> 0000:84:00.0 BAR 4 mmaps[0] [0x0 - 0xffffff]
> . . .
> янв 13 18:17:37 VM qemu-system-x86_64[7131]: 
> vfio_listener_region_add_ram region_add [ram] 0xf8000000 - 0xf8005fff 
> [0x7f691e800000]
> янв 13 18:17:37 VM qemu-system-x86_64[7131]: 
> vfio_listener_region_add_ram region_add [ram] 0xf8007000 - 0xf8ffffff 
> [0x7f691e807000]
> янв 13 18:17:37 VM qemu-system-x86_64[7131]: 
> vfio_listener_region_add_ram region_add [ram] 0xfa000000 - 0xfa000fff 
> [0x7f6b5de37000]
> янв 13 18:17:37 VM qemu-system-x86_64[7131]: 
> vfio_listener_region_add_ram region_add [ram] 0xfa001000 - 0xfa001fff 
> [0x7f6b58004000]
> янв 13 18:17:37 VM qemu-system-x86_64[7131]: 
> vfio_listener_region_add_ram region_add [ram] 0xf9000000 - 0xf9ffffff 
> [0x7f691d800000]
> 
> I use qemu 4.0.0 which I rebuild for tracing support 
> (--enable-trace-backends=syslog).
> 
> Please, help me solve this issue. Thank you!

Something has probably created a QEMU MemoryRegion overlapping the BAR,
we do this for quirks where we want to intercept a range of MMIO for
emulation, but the offset 0x6000 on BAR0 doesn't sound familiar to me.
Run the VM with a monitor and see if 'info mtree' provides any info on
the handling of that overlap.  Thanks,

Alex