Re: [PATCH] PPC: Don't sync timebase when inside VM

On 02.03.2012, at 17:20, Scott Wood wrote:

On Fri, Mar 02, 2012 at 03:12:33PM +0100, Alexander Graf wrote:

quoted

When running inside a virtual machine, we can not modify timebase, so
let's just not call the functions for it then.
=20
This resolves hangs when booting e500 SMP guests on overcommitted =

hosts.

quoted

=20
Reported-by: Stuart Yoder <redacted>
Signed-off-by: Alexander Graf <redacted>
---
arch/powerpc/platforms/85xx/smp.c |    7 +++++++
1 files changed, 7 insertions(+), 0 deletions(-)
=20

diff --git a/arch/powerpc/platforms/85xx/smp.c =

b/arch/powerpc/platforms/85xx/smp.c

quoted

index ff42490..d4b6c1f 100644

--- a/arch/powerpc/platforms/85xx/smp.c
+++ b/arch/powerpc/platforms/85xx/smp.c

@@ -249,6 +249,13 @@ void __init mpc85xx_smp_init(void)

		smp_85xx_ops.cause_ipi =3D doorbell_cause_ipi;
	}
=20
+	/* When running under a hypervisor, we can not modify tb */
+	np =3D of_find_node_by_path("/hypervisor");
+	if (np) {
+		smp_85xx_ops.give_timebase =3D NULL;
+		smp_85xx_ops.take_timebase =3D NULL;
+	}
+
	smp_ops =3D &smp_85xx_ops;

=20
Again, for 85xx we should *never* sync the timebase in the kernel,
hypervisor or no.

The code says "if the kexec config option is enabled, do the sync". I'm =
fairly sure it's there for a reason.

Git blame points to the following commit:

commit f933a41e419a954ef90605224e02c3ded78f3372
Author: Matthew McClintock [off-list ref]
Date:   Wed Jul 21 16:14:53 2010 -0500

    powerpc/85xx: kexec for SMP 85xx BookE systems
   =20
    Adds support for kexec on 85xx machines for the BookE platform.
    Including support for SMP machines
   =20
    Based off work from Maxim Uvarov [off-list ref]
    Signed-off-by: Matthew McClintock [off-list ref]
    Signed-off-by: Kumar Gala [off-list ref]


Alex