Michael Neuling [off-list ref] writes:

Aneesh Kumar K.V [off-list ref] wrote:

quoted

Runtime disable transactional memory feature looking at pa-features
device tree entry. This provides a mechanism to disable TM on P8
systems.

What are we actually achieving with this?

PAPR compliance  :) ? Also I wanted to disable guest kernel from doing
TM related save restore. Guest kernel already look at the cpu feature
before doing that. Hence needed a mechanism to disable the feature. 

Things like

static inline void __switch_to_tm(struct task_struct *prev)
{
	if (cpu_has_feature(CPU_FTR_TM)) {
		tm_enable();
		tm_reclaim_task(prev);
	}
}

quoted

Signed-off-by: Aneesh Kumar K.V <redacted>
---
 arch/powerpc/kernel/prom.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/arch/powerpc/kernel/prom.c b/arch/powerpc/kernel/prom.c
index 668aa4791fd7..537bd7e7db0b 100644
--- a/arch/powerpc/kernel/prom.c
+++ b/arch/powerpc/kernel/prom.c

@@ -161,6 +161,11 @@ static struct ibm_pa_feature {
 	{CPU_FTR_NODSISRALIGN, 0, 0,	1, 1, 1},
 	{0, MMU_FTR_CI_LARGE_PAGE, 0,	1, 2, 0},
 	{CPU_FTR_REAL_LE, PPC_FEATURE_TRUE_LE, 5, 0, 0},
+	/*
+	 * We should use CPU_FTR_TM_COMP so that if we disable TM, it won't get
+	 * enabled via device tree
+	 */
+	{CPU_FTR_TM_COMP, 0, 0,		22, 0, 0},

What does this do to guests?  Will it turn TM unavailable into an
illegal instruction?

Good suggestion. I guess it should be facility unavailable interrupt ?
I should also make the sure __init_HFSCR only set HFSCR_TM only if the
cpu feature is enabled ?

-aneesh