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 <kra...@redhat.com> > CC: Avi Kivity <a...@redhat.com> > Signed-off-by: Jan Kiszka <jan.kis...@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 :). Alex