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

[Jan Kiszka]

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 <address@hidden>
>>>> CC: Avi Kivity <address@hidden>
>>>> Signed-off-by: Jan Kiszka <address@hidden>
>>>>   
>>> [...]
>>>
>>>> +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?

Jan

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