Re: [Qemu-devel] [PATCH RFC 0/1] KVM: ioctl for reading/writing guest memory

[Christian Borntraeger <borntraeger@de.ibm.com>]

Am 03.02.2015 um 13:59 schrieb Paolo Bonzini:
> 
> 
> On 03/02/2015 13:11, Thomas Huth wrote:
>> The userspace (QEMU) then can simply call this ioctl when it wants
>> to read or write from/to virtual guest memory. Then kernel then takes
>> the IPTE-lock, walks the MMU table of the guest to find out the
>> physical address that corresponds to the virtual address, copies
>> the requested amount of bytes from the userspace buffer to guest
>> memory or the other way round, and finally frees the IPTE-lock again.
>>
>> Does that sound like a viable solution (IMHO it does ;-))? Or should
>> I maybe try to pursue another approach?
> 
> It looks feasible to me as well.

Yes, we discussed this internally a lot and things are really tricky. The
ipte lock could be exported to userspace, but we might also need to handle
storage keys (and key protection) in an atomic fashion, so this really
looks like the only safe way.
I guess we will give it some more testing, but to me it looks like a good
candidate for kvm/next after 3.20-rc1.


Christian