Re: [Qemu-devel] Is it possible to detect guest OS modifying pte inside QEMU?

[Peter Maydell <peter.maydell@linaro.org>]

On 8 August 2012 08:38, 陳韋任 (Wei-Ren Chen) <chenwj@iis.sinica.edu.tw> wrote:
>   Just for research, we are studying if we can leave the guest page
> table walk to underlying hardware rather than using software emulation
> (like current approach). So, maybe (if *doable*) we can use x86 hardware
> to help us to walk guest (like ARM) page table. The rough idea is we
> have to maintain a x86-format shadow page table for the corresponding
> ARM page table, point host cr3 to the shadow page table, and let x86
> hardware do its job. The problem is, we have to aware that guest is
> modifying its guest page table entry so that we can sync its corrsponding
> shadow page table. But, we still haven't find a good way to know when
> the guest OS is modifying guest page table entry.

Make it read-only for the guest, and then when you get the exception when
the guest tries to write it, you can (a) do what you need to do and (b)
emulate the failing write insn.

-- PMM