From: Anton Blanchard <an...@samba.org>
3.12-stable review patch. If anyone has any objections, please let me know.
===============
commit 733187e29576041ceccf3b82092ca900fc929170 upstream.
commit f13c13a00512 (powerpc: Stop using non-architected shared_proc
field in lppaca) fixed a potential issue with shared/dedicated
partition detection. The old method of detection relied on an
unarchitected field (shared_proc), and this patch switched
to using something architected (a non zero yield_count).
Unfortunately the assertion in the Linux header that yield_count
is only non zero on shared processor partitions is not true. It
turns out dedicated processor partitions can increment yield_count
and as such we falsely detect dedicated partitions as shared.
Fix the comment, and switch back to using the old method.
Signed-off-by: Anton Blanchard <an...@samba.org>
Signed-off-by: Benjamin Herrenschmidt <b...@kernel.crashing.org>
Signed-off-by: Jiri Slaby <jsl...@suse.cz>
---
arch/powerpc/include/asm/lppaca.h | 12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)
diff --git a/arch/powerpc/include/asm/lppaca.h
b/arch/powerpc/include/asm/lppaca.h
index 4470d1e34d23..844c28de7ec0 100644
--- a/arch/powerpc/include/asm/lppaca.h
+++ b/arch/powerpc/include/asm/lppaca.h
@@ -84,8 +84,8 @@ struct lppaca {
* the processor is yielded (either because of an OS yield or a
* hypervisor preempt). An even value implies that the processor is
* currently executing.
- * NOTE: This value will ALWAYS be zero for dedicated processors and
- * will NEVER be zero for shared processors (ie, initialized to a 1).
+ * NOTE: Even dedicated processor partitions can yield so this
+ * field cannot be used to determine if we are shared or dedicated.
*/
volatile __be32 yield_count;
volatile __be32 dispersion_count; /* dispatch changed physical cpu */
@@ -106,15 +106,15 @@ extern struct lppaca lppaca[];
#define lppaca_of(cpu) (*paca[cpu].lppaca_ptr)
/*
- * Old kernels used a reserved bit in the VPA to determine if it was running
- * in shared processor mode. New kernels look for a non zero yield count
- * but KVM still needs to set the bit to keep the old stuff happy.
+ * We are using a non architected field to determine if a partition is
+ * shared or dedicated. This currently works on both KVM and PHYP, but
+ * we will have to transition to something better.
*/
#define LPPACA_OLD_SHARED_PROC 2
static inline bool lppaca_shared_proc(struct lppaca *l)
{
- return l->yield_count != 0;
+ return !!(l->__old_status & LPPACA_OLD_SHARED_PROC);
}
/*
--
2.6.3
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