Re: Max BAR size for passthru?

On 9/15/25 14:58, Chuck Tuffli wrote:
> I'm trying to get PCI passthru of an AMD GPU working, and am seeing
> what I think is a problem mapping the device's BAR into the guest. The
> host shows:
> 
> # pciconf -lbevV pci0:3:0:0
> vgapci0@pci0:3:0:0:    class=0x030000 rev=0xc0 hdr=0x00 vendor=0x1002
> device=0x7590 subvendor=0x148c subdevice=0x2437
>      vendor     = 'Advanced Micro Devices, Inc. [AMD/ATI]'
>      device     = 'Navi 44 [Radeon RX 9060 XT]'
>      class      = display
>      subclass   = VGA
>      bar   [10] = type Prefetchable Memory, range 64, base
> 0x4000000000, size 268435456, enabled
>      bar   [18] = type Prefetchable Memory, range 64, base
> 0x4010000000, size 2097152, enabled
>      bar   [20] = type I/O Port, range 32, base 0x6000, size 256, enabled
>      bar   [24] = type Memory, range 32, base 0x81100000, size 524288, enabled
>    PCI-e errors = Correctable Error Detected
>                   Unsupported Request Detected
>       Non-fatal = Unsupported Request
>       Corrected = Advisory Non-Fatal Error
> 
> (yes, a 256 MiB BAR). After starting the Linux guest, bhyve spits out the error:
> 
> bhyve: pci_passthru: map_pptdev_mmio failed. I've traced this a bit
> and see that vm_map_find returns 3 (KERN_NO_SPACE) with arguments
>      off=0, addr=0x800000000, len=2097152, max_addr=0
> 
> In the guest, lspci reports
> # lspci -s 00:07.0 -v
> 00:07.0 VGA compatible controller: Advanced Micro Devices, Inc.
> [AMD/ATI] Device 7590 (rev c0) (prog-if 00 [VGA controller])
>      Subsystem: Tul Corporation / PowerColor Device 2437
>      Flags: bus master, fast devsel, latency 0
>      Memory at 800000000 (64-bit, prefetchable) [size=256M]
>      Memory at 810000000 (64-bit, prefetchable) [size=2M]
>      I/O ports at 2000 [size=256]
>      Memory at c1000000 (32-bit, non-prefetchable) [size=512K]
>      Expansion ROM at 000c0000 [virtual] [disabled] [size=128K]
> 
> Has anyone run into something like this before? Is this a limit I'm
> bumping into? Suggestions for what to poke next, etc.? TIA!

Hmmm, I think it would be useful if you could dump the effective memory
mappings for the guest PAs (the vm_map passed to vm_map_find) to see why
it is failing.  Note that the request that is failing is for 2M, not
256M, so I'm curious if the address is wrong somehow (why isn't it
0x810000000?)  Might be good to confirm which BAR it is trying to
allocate GPA space for.

-- 
John Baldwin