Re: Guest memory access within hypervisor Inbox x

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Thanks.

On Fri, Sep 27, 2013 at 3:40 PM, Stefan Hajnoczi <stefanha@xxxxxxxxx> wrote:
> On Fri, Sep 27, 2013 at 03:19:28AM +0530, Piyus Kedia wrote:
>> I am working on record replay in KVM. I just want to confirm that KVM
>> doesn't access guest memory except for DMA. The functions
>> kvm_read_guest_page() and kvm_write_guest_page() in kvm_main.c are
>> only used for mmio emulation which access memory that is always
>> emulated. It will be nice if somebody else also confirm this.
>
> kvmclock comes to mind, I think it has a shared page between the guest
> and the host kernel where clock updates are published from host ->
> guest.  I think kvmclock can be disabled by choosing another clocksource
> in the guest Linux kernel.
>
> There are other exceptions like the ivshmem device which is rarely used
> but can provide shared memory between guest <-> host or guest <-> guest.
> I think that memory is an MMIO PCI BAR in the guest just that neither
> kvm.ko nor QEMU may be catch the update if another process on the host
> is writing to it.
>
> Stefan
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