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

On 03/02/2012 10:30 AM, Alexander Graf wrote:

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

quoted

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.

This resolves hangs when booting e500 SMP guests on overcommitted hosts.

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(-)

diff --git a/arch/powerpc/platforms/85xx/smp.c b/arch/powerpc/platforms/85xx/smp.c
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 = doorbell_cause_ipi;
	}

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

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.

Sigh.  I forgot about that.  It's because instead of doing kexec the
simple way, we actually physically reset the core.  We really shouldn't
do that.  And we *really* shouldn't do it just because CONFIG_KEXEC is
defined, regardless of whether we're actually booting from kexec.

-Scott