Re: [announce] [patch] KVM paravirtualization for Linux

Zachary Amsden
2007-01-05T22:50:16Z

Ingo Molnar wrote:
> * Zachary Amsden <zach@vmware.com> wrote:
>
>
>> What you really want is more like
>> EXPORT_SYMBOL_READABLE_GPL(paravirt_ops);
>>
>
> yep. Not a big issue - what is important is to put the paravirt ops into
> the read-only section so that it's somewhat harder for rootkits to
> modify. (Also, it needs to be made clear that this is fundamental,
> lowlevel system functionality written by people under the GPLv2, so that
> if you utilize it beyond its original purpose, using its internals, you
> likely create a work derived from the kernel. Something simple as irq
> disabling probably doesnt qualify, and that we exported to modules for a
> long time, but lots of other details do. So the existence of
> paravirt_ops isnt a free-for all.)
>

I agree completely. It would be nice to have a way to make certain
kernel structures available, but non-mutable to non-GPL modules.

>> But I'm not sure that is technically feasible yet.
>>
>> The kvm code should probably go in kvm.c instead of paravirt.c.
>>
>
> no. This is fundamental architecture boot code, not module code. kvm.c
> should eventually go into kernel/ and arch/*/kernel, not the other way
> around.
>

What I meant was kvm.c in arch/i386/kernel - as symmetric to the other
paravirt-ops modules, which live in arch/i386/kernel/vmi.c / lhype.c,
etc. Either that, or we should move them to be symmetric, but I don't
think paravirt.c is the proper place for kvm specific code.

>
>> Index: linux/drivers/serial/8250.c
>> ===================================================================
>> --- linux.orig/drivers/serial/8250.c
>> +++ linux/drivers/serial/8250.c
>> @@ -1371,7 +1371,7 @@ static irqreturn_t serial8250_interrupt(
>>
>> l = l->next;
>>
>> - if (l == i->head && pass_counter++ > PASS_LIMIT) {
>> + if (!kvm_paravirt
>>
>> Is this a bug that might happen under other virtualizations as well,
>> not just kvm? Perhaps it deserves a disable feature instead of a kvm
>> specific check.
>>
>
> yes - this limit is easily triggered via the KVM/Qemu virtual serial
> drivers. You can think of "kvm_paravirt" as "Linux paravirt", it's just
> a flag.
>

Can't you just test paravirt_enabled() in that case?

Zach