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SubjectRe: [PATCH 3/3] Time to make CONFIG_PARAVIRT non-experimental.
On Tue, 2007-09-18 at 23:52 +0200, Andi Kleen wrote:
> On Tuesday 18 September 2007 23:34, Rusty Russell wrote:
> > How about a "select" based on Xen, lguest or VMI? There's no other
> > reason to enable it, after all.
> I did an patch to do that recently because the current setup
> is indeed unobvious.
> But I had to drop it again because
> it ended up with Kconfig warnings. about undefined symbols
> on x86-64. The problem is that lguest
> is visible in Kconfig for all architectures and it warns
> if you select something that doesn't exist on all architectures.

I think that's fixed as a side-effect of this cleanup. At least, it
works for me on x86-64. Patch below: if you agree, I'll re-xmit all

> > > Also I would still consider it experimental.
> >
> > After 9 months in mainline and three kernel versions,
> Well it changed a lot each release.

Well, the biggest change was the patching code getting enhanced in
2.6.22 (to cover all calls, not just 5). The 22 -> 23 changes were
fairly trivial.

So I think 2.6.24 is a reasonable time to remove EXPERIMENTAL.

> > I'd hope not.
> > It's been pretty damn stable (ok, you broke it once, but maybe that's
> > because you consider it experimental).
> Is there a significant user base?

It's enabled in Ubuntu Feisty (2.6.20).

> At least the Xen port seems to have specific requirements
> and essentially only work on xen-unstable (?) [or at least
> some very new Xen version] which probably very few
> people use.

Sure, and that might well still be experimental (Jeremy?). But that's

Hope that helps,
Andi points out that PARAVIRT is an option best selected when needed.

We introduce PARAVIRT_GUEST for the menu itself, and select PARAVIRT
if they ask for anything which needs it. This also makes PARAVIRT

Signed-off-by: Rusty Russell <>

diff -r 8efa5fdb22d8 arch/i386/Kconfig
--- a/arch/i386/Kconfig Wed Sep 19 11:23:18 2007 +1000
+++ b/arch/i386/Kconfig Wed Sep 19 11:33:59 2007 +1000
@@ -214,24 +214,30 @@ config X86_ES7000


-menuconfig PARAVIRT
+config PARAVIRT
+ bool
+ depends on !(X86_VISWS || X86_VOYAGER)
+ help
+ This changes the kernel so it can modify itself when it is run
+ under a hypervisor, potentially improving performance significantly
+ over full virtualization. However, when run without a hypervisor
+ the kernel is theoretically slower and slightly larger.
+menuconfig PARAVIRT_GUEST
- bool "Paravirtualized guest support (EXPERIMENTAL)"
- depends on EXPERIMENTAL
+ bool "Paravirtualized guest support"
- depends on !(X86_VISWS || X86_VOYAGER)
- help
- Paravirtualization is a way of running multiple instances of
- Linux on the same machine, under a hypervisor. This option
- changes the kernel so it can modify itself when it is run
- under a hypervisor, improving performance significantly.
- However, when run without a hypervisor the kernel is
- theoretically slower. If in doubt, say N.
+ help
+ Say Y here to get to see options related to running Linux under
+ various hypervisors. This option alone does not add any kernel code.
+ If you say N, all options in this submenu will be skipped and disabled.

source "arch/i386/xen/Kconfig"

config VMI
bool "VMI Guest support"
+ select PARAVIRT
VMI provides a paravirtualized interface to the VMware ESX server
(it could be used by other hypervisors in theory too, but is not
@@ -239,6 +246,7 @@ config VMI

bool "Lguest guest support"
+ select PARAVIRT
depends on !X86_PAE
Lguest is a tiny in-kernel hypervisor. Selecting this will
diff -r 8efa5fdb22d8 arch/i386/xen/Kconfig
--- a/arch/i386/xen/Kconfig Wed Sep 19 11:23:18 2007 +1000
+++ b/arch/i386/xen/Kconfig Wed Sep 19 11:25:07 2007 +1000
@@ -4,6 +4,7 @@

config XEN
bool "Xen guest support"
+ select PARAVIRT
This is the Linux Xen port. Enabling this will allow the

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