Re: Scheduling of VCPUs and allocation of Guest Physical Memory

[Anthony Liguori <anthony@codemonkey.ws>]

Sukanto Ghosh wrote:
>>> ii) Who does the allocation of host physical memory to the guest, is 
>>> it KVM module or the associated QEmu process ?
>>
>> The QEMU process allocates the memory via malloc().
> Doesn't the QEMU process and the guest have different address-spaces ? 
> So, how can it malloc for the guest ? I thought the QEMU process 
> requests for the memory allocation to the kvm module via the /dev/kvm 
> device node.

Yes, the guest has a different address space from the host.  The QEMU 
process malloc()'s the physical memory for the guest, and tells KVM what 
the region is (via an ioctl to /dev/kvm).  When the guest tries to 
create an address space mapping a guest VA to a guest PA, KVM will build 
that mapping by using virtual memory allocated by QEMU.  To do this, it 
uses the mapping to translate guest PA to host PA.  Then it will build 
an address space for the guest mapping guest VA to host PA.

Regards,

Anthony Liguori

>
> Thanks and regards
> Sukanto
>
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