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

[Alexander Graf]

On 12.09.2011, at 22:21, Blue Swirl wrote:

> 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.

Yeah, usually the ISA bus is behind an ISA-PCI bridge, so it should inherit the 
offset from its parent. Or do you mean something different?


Alex