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

Zachary Amsden
2007-01-05T22:15:22Z

Ingo Molnar wrote:
> i'm pleased to announce the first release of paravirtualized KVM (Linux
> under Linux), which includes support for the hardware cr3-cache feature
> of Intel-VMX CPUs. (which speeds up context switches and TLB flushes)
>
> the patch is against 2.6.20-rc3 + KVM trunk and can be found at:
>
> http://redhat.com/~mingo/kvm-paravirt-patches/
>
> Some aspects of the code are still a bit ad-hoc and incomplete, but the
> code is stable enough in my testing and i'd like to have some feedback.
>

Your code looks generally good. I have some comments.

You can't do this, even though you want to:

-EXPORT_SYMBOL(paravirt_ops);
+EXPORT_SYMBOL_GPL(paravirt_ops);

The problem is it makes all modules GPL - or at least all modules that
use any kind of locking, pull in the basic definitions to enable and
disable interrupts, thus the paravirt_ops symbol, so basically all modules.

What you really want is more like EXPORT_SYMBOL_READABLE_GPL(paravirt_ops);

But I'm not sure that is technically feasible yet.

The kvm code should probably go in kvm.c instead of paravirt.c.

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.

Which also gets rid of the need for this unusually placed extern:

Index: linux/include/linux/sched.h
===================================================================
--- linux.orig/include/linux/sched.h
+++ linux/include/linux/sched.h
@@ -1911,6 +1911,11 @@ static inline void set_task_cpu(struct t

#endif /* CONFIG_SMP */

+/*
+ * Is paravirtualization active?
+ */
+extern int kvm_paravirt;

+