Anthony Liguori wrote:
Mathias Gottschlag wrote:
Grub inits the CPU with no paging and flat segmenting, I now activate
segments to move the code to 0xE0000000 and later activate paging and
reset the segments. When I run this code on qemu or on real hardware
(Athlon XP), everything works well, but on kvm I get several hangs.
For example I try to write to 0xE00B8000 to write into the VGA
framebuffer. This addres should now get translated back to 0xB8000 by
the segment which has the base address 0x20000000, and this
definately works on real hardware, but on kvm I only notice a hang at
the instruction which writes at that address (kvm still responds, but
doesn't update eip anymore, execution stops.
I looked briefly and there didn't appear to be any explicit checks for
wrap around but I think that it will work correctly since we're always
using at least unsigned long in the host. My suspicion is that we're
somehow getting something wrong with MMIO decoding.
Well, unsigned long is 64-bits on a 64-bit host, so the generated
address will be 0x1000b8000 instead of 0xb8000. So the problem here is
likely to be a missing wraparound, rather than a wraparound.
--
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.
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