Re: PCI device passthrough / memory mapping issue

[Avi Kivity <avi@redhat.com>]

On 03/19/2010 12:46 AM, Fede wrote:
> I'm currently working to enable vga passthrough in kvm.
>    

> assigned_dev_iomem_map: e_phys=10000000 r_virt=0x7fa64af0e000 type=0
> len=02000000 region_num=3
> kvm_register_phys_mem:580 memory: gpa: 10000000, size: 2000000, uaddr:
> 7fa64af0e000, slot: 7,flags: 0
> create_userspace_phys_mem: File exists
> assigned_dev_iomem_map: Error: create new mapping failed
>
>
> This worked a month ago. But after some git updates there's a problem.
>
> When the real device regions are mapped from real virtual memory to
> guest physical addresses in kvm, it overlaps region 3 with the guest
> physical memory assigned to kernel space (0x10000000 to 0x10200000)
>
> I've been trying to look for the answer to this question: Why is gpa
> 0x10000000 chosen and not any other free memory space?
>    

The BIOS generally assigns addresses, then the OS updates them if it 
wants to.  Is the crash before or after the OS has started loading?

If before, suggest you add some printfs to seabios to explain its decisions.

> It seems that this addresses are being chosen here (for example, for region 3):
> assigned_dev_pci_read_config: (4.0): address=001c val=0x00000000 len=4
> assigned_dev_pci_write_config: (4.0): address=001c val=0xffffffff len=4
> assigned_dev_pci_read_config: (4.0): address=001c val=0xfe000000 len=4
>    

The above sequence is how the bios determines the BAR size. (0x2000000 
in this case).

> assigned_dev_pci_write_config: (4.0): address=001c val=0x00000000 len=4
>    

Now it clears the mess from the previous step.

> assigned_dev_pci_read_config: (4.0): address=001c val=0x00000000 len=4
> assigned_dev_pci_write_config: (4.0): address=001c val=0x10000000 len=4
>    

Here it assigns a new address.  It's clearly wrong.  A log in seabios 
will explain this.

> What does this mean? Why PCI BARs are being written and read?

> Why the
> values that are written differs from the ones that are read after?
>    

BARs are not RAM cells.  the least significant address bits are 
hardwired to zero, that's how the BIOS detects the BAR size (and 
required alignment).

> The last write is the gpa that is used.
>
> Is this a bug? I can't find the source of this gpa addresses. I need
> to change them.
>    

Looks like a bug in seabios.

-- 
error compiling committee.c: too many arguments to function