Re: PCIe device paththrough via vfio issue

[Alex Williamson]

On Tue, 14 Jan 2020 17:14:33 +1100
Alexey Kardashevskiy <address@hidden> wrote:

> On 14/01/2020 03:28, Alex Williamson wrote:
> > On Mon, 13 Jan 2020 18:49:21 +0300
> > yurij <address@hidden> 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,  
> 
> 
> Could not it be an MSIX region? 'info mtree -f' should tell exactly what
> is going on.

Oh, good call, that's probably it.  The PCI spec specifically
recommends against placing non-MSIX related registers within the same
4K page as the vector table to avoid such things:

 If a Base Address register that maps address space for the MSI-X Table
 or MSI-X PBA also maps other usable address space that is not
 associated with MSI-X structures, locations (e.g., for CSRs) used in
 the other address space must not share any naturally aligned 4-KB
 address range with one where either MSI-X structure resides. This
 allows system software where applicable to use different processor
 attributes for MSI-X structures and the other address space.

We have the following QEMU vfio-pci device option to relocate the BAR
elsewhere for hardware that violates that recommendation or for where
the PCI spec recommended alignment isn't sufficient:

 x-msix-relocation=<OffAutoPCIBAR> - off/auto/bar0/bar1/bar2/bar3/bar4/bar5

In this case I'd probably recommend bar2 or bar3 as those BARs would
only be extended to 8K versus bar0/4 would be extended to 32M.  Thanks,

Alex