[0/4] vfio/igd: remove incorrect IO BAR4 quirk

Message

Tomita Moeko Jan. 22, 2025, 5:17 p.m. UTC

Based on experiments and reverse engineering about the mysterious IO
BAR4, it appears that the current quirk implementation is incorrect.
As discussed in a previous mail thread [1], current implementation
believes VBIOS is writing HPA of Data Stolen Memory (DSM) in GTT
entries, so it intercepts and writes (addr - Host BDSM + Guest BDSM)
instead, probably believes the addresses are hardcoded in VBIOS.

With disassembling a VBIOS of Intel Sandy/Ivy Bridge and Haswell [2]
(thankfully there is only a few 32-bit out instructions), VBIOS read
BDSM from pci config space, which is programmed by SeaBIOS [3] in
guest. That is to say, VBIOS actually writes GPA when programming GTT
initial entries, the current quirk is incorrect.

The change was tested on a Kaby Lake HD620 (Gen 9) by comparing GTT
entries read from MMIO BAR0 and IO BAR4.

This patchset also creates a new function vfio_config_quirk_setup()
for the config space quirk previously in vfio_probe_igd_bar4_quirk().
The OpRegion quirk in vfio_realize() will also be moved to it in a
later change, so that all the IGD-related quirks can be put in igd.c.

[1] https://lore.kernel.org/qemu-devel/[e-mail]/
[2] https://winraid.level1techs.com/t/offer-intel-sandy-ivy-bridge-and-haswell-vbios-modules/30272
[3] https://gitlab.com/qemu-project/seabios/-/blob/1.12-stable/src/fw/pciinit.c#L319-332

Related VBIOS disassembly:

# read BDSM
6498:	66 53                	push   %ebx
649a:	66 2e 83 3e 94 64 00 	cmpl   $0x0,%cs:0x6494  # BDSM already read?
64a1:	74 07                	je     0x64aa
64a3:	66 2e a1 94 64       	mov    %cs:0x6494,%eax 
64a8:	eb 0f                	jmp    0x64b9
64aa:	b8 5e 10             	mov    $0x105e,%ax      # 5e == 5c + 2, that's why shl 16 later?
                                                    # ((2 << 11) + 0x5e)
64ad:	e8 55 05             	call   0x6a05           # read config space via port cf8/cfc
64b0:	66 c1 e0 10          	shl    $0x10,%eax       # eax << 16
64b4:	66 2e a3 94 64       	mov    %eax,%cs:0x6494  # save BDSM
64b9:	66 5b                	pop    %ebx
64bb:	c3                   	ret
# program single GTT entry, esi: addr, eax: data
6d16:	66 50                	push   %eax
6d18:	52                   	push   %dx
6d19:	2e 8b 16 4a e4       	mov    %cs:-0x1bb6,%dx  # saved MMIO_Index port
6d1e:	66 96                	xchg   %eax,%esi
6d20:	66 ef                	out    %eax,(%dx)       # write MMIO_Index
6d22:	2e 8b 16 4c e4       	mov    %cs:-0x1bb4,%dx  # saved MMIO_Data port
6d27:	66 96                	xchg   %eax,%esi
6d29:	66 83 c8 01          	or     $0x1,%eax        # set valid bit
6d2d:	66 ef                	out    %eax,(%dx)       # write MMIO_Data
6d2f:	5a                   	pop    %dx
6d30:	66 58                	pop    %eax
6d32:	c3                   	ret
# program GTT entries, esi: entry addr, eax: page addr
e929:	51                   	push   %cx
e92a:	e8 6b 7b             	call   0x6498       # read BDSM
e92d:	25 00 e0             	and    $0xe000,%ax
e930:	66 83 c8 01          	or     $0x1,%eax    # valid bit
e934:	66 be 01 00 00 00    	mov    $0x1,%esi    # gtt access bit in addr
e93a:	e8 d9 83             	call   0x6d16       # single entry routine
e93d:	66 83 c6 04          	add    $0x4,%esi    # next entry
e941:	66 05 00 10 00 00    	add    $0x1000,%eax # next page
e947:	e2 f1                	loop   0xe93a
e949:	59                   	pop    %cx
e94a:	c3                   	ret

Observed layout of the undocumented MMIO_Index register:
 31                                                   2   1      0
+-------------------------------------------------------------------+
|                        Offset                        | Rsvd | Sel |
+-------------------------------------------------------------------+
- Offset: Byte offset in specified region, 4-byte aligned.
- Sel: Region selector
       0: MMIO register region (first half of MMIO BAR0)
       1: GTT region (second half of MMIO BAR0). Pre Gen11 only.

Tomita Moeko (4):
  vfio/igd: remove GTT write quirk in IO BAR 4
  vfio/pci: add placeholder for device-specific config space quirks
  vfio/igd: refactor vfio_probe_igd_bar4_quirk() into pci config quirk
  vfio/igd: do not include GTT stolen size in etc/igd-bdsm-size

 hw/vfio/igd.c        | 247 ++++---------------------------------------
 hw/vfio/pci-quirks.c |  11 +-
 hw/vfio/pci.c        |   4 +
 hw/vfio/pci.h        |   3 +-
 4 files changed, 35 insertions(+), 230 deletions(-)