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

[Blue Swirl]

On Mon, Sep 12, 2011 at 3:20 PM, Alexander Graf <address@hidden> 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 :).

I had similar problems with sun4u, fixed with
f69539b14bdba7a5cd22e1f4bed439b476b17286. I think also here, PCI
should be given a memory range at 0x80000000 and VGA should
automatically use that like.