Re: [Qemu-devel] [PATCH v3 5/6] vga: Use linear mapping + dirty logging in chain 4 memory access mode

[Jan Kiszka <jan.kiszka@siemens.com>]

On 2011-09-13 09:39, Alexander Graf wrote:
> 
> On 12.09.2011, at 17:57, Jan Kiszka wrote:
> 
>> On 2011-09-12 17:49, Jan Kiszka wrote:
>>> On 2011-09-12 17:45, Andreas Färber wrote:
>>>> Am 12.09.2011 17:33, schrieb Jan Kiszka:
>>>>> On 2011-09-12 17:20, Alexander Graf wrote:
>>>>>> Jan Kiszka wrote:
>>>>>>> Most VGA memory access modes require MMIO handling as they demand weird
>>>>>>> logic to get a byte from or into the video RAM. However, there is one
>>>>>>> exception: chain 4 mode with all memory planes enabled for writing. This
>>>>>>> mode actually allows lineary mapping, which can then be combined with
>>>>>>> dirty logging to accelerate KVM.
>>>>>>>
>>>>>>> This patch accelerates specifically VBE accesses like they are used by
>>>>>>> grub in graphical mode. Not only the standard VGA adapter benefits from
>>>>>>> this, also vmware and spice in VGA mode.
>>>>>>>
>>>>>>> CC: Gerd Hoffmann <kraxel@redhat.com>
>>>>>>> CC: Avi Kivity <avi@redhat.com>
>>>>>>> Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
>>>>>>>
>>>>>> [...]
>>>>>>
>>>>>>> +static void vga_update_memory_access(VGACommonState *s)
>>>>>>> +{
>>>>>>> +    MemoryRegion *region, *old_region = s->chain4_alias;
>>>>>>> +    target_phys_addr_t base, offset, size;
>>>>>>> +
>>>>>>> +    s->chain4_alias = NULL;
>>>>>>> +
>>>>>>> +    if ((s->sr[0x02] & 0xf) == 0xf && s->sr[0x04] & 0x08) {
>>>>>>> +        offset = 0;
>>>>>>> +        switch ((s->gr[6] >> 2) & 3) {
>>>>>>> +        case 0:
>>>>>>> +            base = 0xa0000;
>>>>>>> +            size = 0x20000;
>>>>>>> +            break;
>>>>>>> +        case 1:
>>>>>>> +            base = 0xa0000;
>>>>>>> +            size = 0x10000;
>>>>>>> +            offset = s->bank_offset;
>>>>>>> +            break;
>>>>>>> +        case 2:
>>>>>>> +            base = 0xb0000;
>>>>>>> +            size = 0x8000;
>>>>>>> +            break;
>>>>>>> +        case 3:
>>>>>>> +            base = 0xb8000;
>>>>>>> +            size = 0x8000;
>>>>>>> +            break;
>>>>>>> +        }
>>>>>>> +        region = g_malloc(sizeof(*region));
>>>>>>> +        memory_region_init_alias(region, "vga.chain4", &s->vram, offset, size);
>>>>>>> +        memory_region_add_subregion_overlap(s->legacy_address_space, base,
>>>>>>> +                                            region, 2);
>>>>>>>
>>>>>> This one eventually gives me the following in info mtree with -M g3beige
>>>>>> on qemu-system-ppc:
>>>>>>
>>>>>> (qemu) info mtree
>>>>>> memory
>>>>>> system addr 00000000 off 00000000 size 7fffffffffffffff
>>>>>> -vga.chain4 addr 000a0000 off 00000000 size 10000
>>>>>> -macio addr 80880000 off 00000000 size 80000
>>>>>> --macio-nvram addr 00060000 off 00000000 size 20000
>>>>>> --pmac-ide addr 00020000 off 00000000 size 1000
>>>>>> --cuda addr 00016000 off 00000000 size 2000
>>>>>> --escc-bar addr 00013000 off 00000000 size 40
>>>>>> --dbdma addr 00008000 off 00000000 size 1000
>>>>>> --heathrow-pic addr 00000000 off 00000000 size 1000
>>>>>> -vga.rom addr 80800000 off 00000000 size 10000
>>>>>> -vga.vram addr 80000000 off 00000000 size 800000
>>>>>> -vga-lowmem addr 800a0000 off 00000000 size 20000
>>>>>> -escc addr 80013000 off 00000000 size 40
>>>>>> -isa-mmio addr fe000000 off 00000000 size 200000
>>>>>> I/O
>>>>>> io addr 00000000 off 00000000 size 10000
>>>>>> -cmd646-bmdma addr 00000700 off 00000000 size 10
>>>>>> --cmd646-bmdma-ioport addr 0000000c off 00000000 size 4
>>>>>> --cmd646-bmdma-bus addr 00000008 off 00000000 size 4
>>>>>> --cmd646-bmdma-ioport addr 00000004 off 00000000 size 4
>>>>>> --cmd646-bmdma-bus addr 00000000 off 00000000 size 4
>>>>>> -cmd646-cmd addr 00000680 off 00000000 size 4
>>>>>> -cmd646-data addr 00000600 off 00000000 size 8
>>>>>> -cmd646-cmd addr 00000580 off 00000000 size 4
>>>>>> -cmd646-data addr 00000500 off 00000000 size 8
>>>>>> -ne2000 addr 00000400 off 00000000 size 100
>>>>>>
>>>>>> This ends up overmapping 0xa0000, effectively overwriting kernel data.
>>>>>> If I #if 0 the offending chunk out, everything is fine. I would assume
>>>>>> that chain4 really needs to be inside of lowmem? No idea about VGA, but
>>>>>> I'm sure you know what's going on :).
>>>>> Does this help?
>>>>>
>>>>> diff --git a/hw/vga.c b/hw/vga.c
>>>>> index 125fb29..0a0c5a6 100644
>>>>> --- a/hw/vga.c
>>>>> +++ b/hw/vga.c
>>>>> @@ -181,6 +181,7 @@ static void vga_update_memory_access(VGACommonState *s)
>>>>>             size = 0x8000;
>>>>>             break;
>>>>>         }
>>>>> +        base += isa_mem_base;
>>>>>         region = g_malloc(sizeof(*region));
>>>>>         memory_region_init_alias(region, "vga.chain4", &s->vram, offset, size);
>>>>>         memory_region_add_subregion_overlap(s->legacy_address_space, base,
>>>>
>>>> No longer oopses, but the screen looks chaotic now (black bar at bottom,
>>>> part of contents at top etc.).
>>>
>>> Does this PPC machine map the ISA range and forward VGA accesses to the
>>> adapter in general?
>>
>> If it does, please post a dump of the VGACommonState while the screen is
>> corrupted (gdb or via device_show [1]. Maybe I missed some condition
>> that prevents chain4 optimizations, and your guest triggers this.
> 
> Picture: http://dl.dropbox.com/u/8976842/qemu/Screen%20shot%202011-09-13%20at%2009.37.15.png
> 
> (qemu) info qtree 
> bus: main-system-bus
>   type System
>   dev: fw_cfg, id "#8"
>     dev-prop: ctl_iobase = 0x0
>     dev-prop: data_iobase = 0x0
>     irq 0
>     mmio f0000510/00000002
>     mmio f0000512/00000002
>   dev: escc, id "#4"
>     dev-prop: frequency = 3686400
>     dev-prop: it_shift = 4
>     dev-prop: disabled = 0
>     dev-prop: disabled = 0
>     dev-prop: chnBtype = 0
>     dev-prop: chnAtype = 0
>     dev-prop: chrB = <null>
>     dev-prop: chrA = serial0
>     irq 2
>     mmio 80013000/00000040
>   dev: grackle, id "#1"
>     irq 0
>     mmio fec00000/00001000
>     mmio fee00000/00001000
>     bus: pci
>       type PCI
>       dev: cmd646-ide, id "#6"
>         dev-prop: secondary = 0
>         bus-prop: addr = 03.0
>         bus-prop: romfile = <null>
>         bus-prop: rombar = 1
>         bus-prop: multifunction = off
>         bus-prop: command_serr_enable = on
>         class IDE controller, addr 00:03.0, pci id 1095:0646 (sub 1af4:1100)
>         bar 0: i/o at 0x500 [0x507]
>         bar 1: i/o at 0x580 [0x583]
>         bar 2: i/o at 0x600 [0x607]
>         bar 3: i/o at 0x680 [0x683]
>         bar 4: i/o at 0x700 [0x70f]
>         bus: ide.1
>           type IDE
>         bus: ide.0
>           type IDE
>           dev: ide-cd, id "#7"
>             dev-prop: drive = ide1-cd0
>             dev-prop: logical_block_size = 512
>             dev-prop: physical_block_size = 512
>             dev-prop: min_io_size = 0
>             dev-prop: opt_io_size = 0
>             dev-prop: bootindex = -1
>             dev-prop: discard_granularity = 0
>             dev-prop: ver = "0.15.50"
>             dev-prop: serial = "QM00003"
>             bus-prop: unit = 0
>       dev: ne2k_pci, id "#5"
>         dev-prop: mac = 52:54:00:12:34:56
>         dev-prop: vlan = 0
>         dev-prop: netdev = <null>
>         dev-prop: bootindex = -1
>         bus-prop: addr = 02.0
>         bus-prop: romfile = <null>
>         bus-prop: rombar = 1
>         bus-prop: multifunction = off
>         bus-prop: command_serr_enable = on
>         class Ethernet controller, addr 00:02.0, pci id 10ec:8029 (sub 1af4:1100)
>         bar 0: i/o at 0x400 [0x4ff]
>       dev: VGA, id "#3"
>         bus-prop: addr = 01.0
>         bus-prop: romfile = "vgabios-stdvga.bin"
>         bus-prop: rombar = 1
>         bus-prop: multifunction = off
>         bus-prop: command_serr_enable = on
>         class VGA controller, addr 00:01.0, pci id 1234:1111 (sub 1af4:1100)
>         bar 0: mem at 0x80000000 [0x807fffff]
>         bar 6: mem at 0x80800000 [0x8080ffff]
>       dev: grackle, id "#2"
>         bus-prop: addr = 00.0
>         bus-prop: romfile = <null>
>         bus-prop: rombar = 1
>         bus-prop: multifunction = off
>         bus-prop: command_serr_enable = on
>         class Host bridge, addr 00:00.0, pci id 1057:0002 (sub 1af4:1100)
> 
> 
> 
> (qemu) device_show #3
> dev: VGA, id "#3", version 2
>   dev.
>     version_id:         00000002
>     config:             00 00 00 00 10 d1 cf 20 - 00 00 00 00 10 d1 d0 30
>                         ...
>     irq_state:          00 00 00 00 00 00 00 10 - 00 00 00 00 00 00 00 00
>   vga.
>     latch:              00000000
>     sr_index:           00
>     sr:                 00 00 0f 00 08 00 00 00
>     gr_index:           00
>     gr:                 00 00 00 00 00 40 05 00 - 00 00 00 00 00 00 00 00
>     ar_index:           20
>     ar:                 00 00 00 00 00 00 00 00 - 00 00 00 00 00 00 00 00
>                         ...
>     ar_flip_flop:       00000001
>     cr_index:           00
>     cr:                 00 63 00 00 00 00 00 50 - 00 40 00 00 00 00 00 00
>                         ...
>     msr:                00
>     fcr:                00
>     st00:               00
>     st01:               00
>     dac_state:          00
>     dac_sub_index:      00
>     dac_read_index:     00
>     dac_write_index:    10
>     dac_cache:          3f 3f 3f
>     palette:            00 00 00 00 00 2a 00 2a - 00 00 2a 2a 2a 00 00 2a
>                         ...
>     bank_offset:        00000000
>     is_vbe_vmstate:     01
>     vbe_index:          0004
>     vbe_regs[00]:       b0c5
>     vbe_regs[01]:       0320
>     vbe_regs[02]:       0258
>     vbe_regs[03]:       000f
>     vbe_regs[04]:       0001
>     vbe_regs[05]:       0000
>     vbe_regs[06]:       0320
>     vbe_regs[07]:       0258
>     vbe_regs[08]:       0000
>     vbe_regs[09]:       0000
>     vbe_start_addr:     00000000
>     vbe_line_offset:    00000640
>     vbe_bank_mask:      0000007f
> 

Makes no sense, must work with this setup. Maybe it's dynamic effect
when switching modes of bank offsets. Do you have some test image for me?

Jan

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