Re: [Qemu-devel] [PATCH V3 WIP 3/3] disable vhost_verify_ring_mappings check

[Paolo Bonzini]

Il 28/03/2013 10:04, Michael S. Tsirkin ha scritto:
>>> > > Got ranges_overlap for vq: 0 ring_phys: 0 ring_size: 1028
>>> > > Checking vq: 1 ring_phys: 0 ring_size: 1028 >>>>>>>>>>>>>>>>>>.
>>> > > Got ranges_overlap for vq: 1 ring_phys: 0 ring_size: 1028
>>> > > Checking vq: 2 ring_phys: ed000 ring_size: 5124 >>>>>>>>>>>>>>>>>>.
>>> > > Calling l: 5124 for start_addr: c0000 for vq 2
>>> > > Unable to map ring buffer for ring 2
>>> > > l: 4096 ring_size: 5124
> okay so the ring address is within ROM.
> Unsurprisingly it fails.
> bios should stop device before write protect.
> 

The above log is very early, when everything is RAM:

  vhost_set_memory: section: 0x7fe2801f2b60 section->size: 2146697216 add: 0
  Before vhost_verify_ring_mappings: start_addr: c0000 size: 2146697216

The rings are not within ROM.  ROM is at 0xc0000-0xcc000 according to the
PAM registers.

The way I followed the debug output, "Got ranges_overlap" means 
actually "bailing out because ranges do not overlap".  In particular, 
here all three virtqueues fail the test, because this is the ROM area 
0xc0000..0xc7fff:

  vhost_set_memory: section: 0x7fe2801f2aa0 section->size: 32768 add: 1
  Before vhost_verify_ring_mappings: start_addr: c0000 size: 32768
  Checking vq: 0 ring_phys: 0 ring_size: 1028 >>>>>>>>>>>>>>>>>>.
  Got ranges_overlap for vq: 0 ring_phys: 0 ring_size: 1028
  Checking vq: 1 ring_phys: 0 ring_size: 1028 >>>>>>>>>>>>>>>>>>.
  Got ranges_overlap for vq: 1 ring_phys: 0 ring_size: 1028
  Checking vq: 2 ring_phys: ed000 ring_size: 5124 >>>>>>>>>>>>>>>>>>.
  Got ranges_overlap for vq: 2 ring_phys: ed000 ring_size: 5124

Just below, vhost looks at the large RAM area starting at 0xc8000
(it's large because 0xf0000..0xfffff is still RAM):

  vhost_set_memory: section: 0x7fe2801f2aa0 section->size: 2146664448 add: 1
  Before vhost_verify_ring_mappings: start_addr: c8000 size: 2146664448
  Checking vq: 0 ring_phys: 0 ring_size: 1028 >>>>>>>>>>>>>>>>>>.
  Got ranges_overlap for vq: 0 ring_phys: 0 ring_size: 1028
  Checking vq: 1 ring_phys: 0 ring_size: 1028 >>>>>>>>>>>>>>>>>>.
  Got ranges_overlap for vq: 1 ring_phys: 0 ring_size: 1028
  Checking vq: 2 ring_phys: ed000 ring_size: 5124 >>>>>>>>>>>>>>>>>>.
  Calling l: 5124 for start_addr: c8000 for vq 2

Here vq 0 and 1 fail the test because they are in low RAM, vq 2 passes.

After 0xf0000..0xfffff is marked readonly, vhost looks at the RAM
between 0xc9000 and 0xf0000:

  vhost_set_memory: section: 0x7fe2801f2aa0 section->size: 159744 add: 1
  Before vhost_verify_ring_mappings: start_addr: c9000 size: 159744
  Checking vq: 0 ring_phys: 0 ring_size: 1028 >>>>>>>>>>>>>>>>>>.
  Got ranges_overlap for vq: 0 ring_phys: 0 ring_size: 1028
  Checking vq: 1 ring_phys: 0 ring_size: 1028 >>>>>>>>>>>>>>>>>>.
  Got ranges_overlap for vq: 1 ring_phys: 0 ring_size: 1028
  Checking vq: 2 ring_phys: ed000 ring_size: 5124 >>>>>>>>>>>>>>>>>>.
  Calling l: 5124 for start_addr: c9000 for vq 2

and the ROM between 0xf0000 and 0xfffff, which no ring overlaps with:

  vhost_set_memory: section: 0x7fe2801f2aa0 section->size: 65536 add: 1
  Before vhost_verify_ring_mappings: start_addr: f0000 size: 65536
  Checking vq: 0 ring_phys: 0 ring_size: 1028 >>>>>>>>>>>>>>>>>>.
  Got ranges_overlap for vq: 0 ring_phys: 0 ring_size: 1028
  Checking vq: 1 ring_phys: 0 ring_size: 1028 >>>>>>>>>>>>>>>>>>.
  Got ranges_overlap for vq: 1 ring_phys: 0 ring_size: 1028
  Checking vq: 2 ring_phys: ed000 ring_size: 5124 >>>>>>>>>>>>>>>>>>.
  Got ranges_overlap for vq: 2 ring_phys: ed000 ring_size: 5124



SeaBIOS is indeed not initializing vqs 0/1 (the control and event 
queues), so their ring_phys is 0.  But the one that is failing is vq 2, 
the first request queue.

Your patch seems good, but shouldn't fix this problem.

Paolo