Re: [PATCH]: Fix memory corruption in-kernel IOAPIC emulation

[Avi Kivity <avi-atKUWr5tajBWk0Htik3J/w@public.gmane.org>]

Chris Lalancette wrote:
> Avi Kivity wrote:
>   
>> Excellent catch, but the fix is wrong.  Instead of partially restoring 
>> the ioapic state in the kernel, you should fully save it in qemu.
>>
>> This is a trap that many fall into: considering kvm and qemu as one 
>> entity and making sure they work well together.  We need to make sure 
>> that kvm and libkvm are useful for other userspace programs as well.
>>
>>     
>
> Actually, let me ask a question here.  It seems to me that there are two
> ways I could go about this:
>
> 1)  Change the save protocol so that it saves the relevant information
> (i.e. base_address and irr), and then the restore protocol so it
> actually pulls this stuff off the wire.  This solution seems more
> "right" to me, but it has the downside that we are changing the
> over-the-wire information, which will break migration between old and
> new versions of qemu.
>
>   

qemu supports backwards compatible changes to the protocol via the 
version field.

> 2)  Just change the restore protocol so that we properly fill in the
> missing fields with real, hard-coded values instead of just random
> memory.  This has the benefit that it doesn't change the protocol, but
> has the downside that we won't reflect changes to base_address or irr
> 100% properly.  In practice, this doesn't seem like a big deal since
> there doesn't currently seem to be a way to change base_address anyway,
> and losing the irr doesn't seem to be catastrophic (although I'm not
> 100% certain about that).
>
> The attached patch implements 2); does anyone have an opinion on which
> way to go here?
>   

I prefer doing a full save/restore, since we don't know what guests 
depend on.

-- 
error compiling committee.c: too many arguments to function


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