This is a note to let you know that I've just added the patch titled KVM: PPC: Book3S HV: Don't dynamically split core when already split to the 4.3-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: kvm-ppc-book3s-hv-don-t-dynamically-split-core-when-already-split.patch and it can be found in the queue-4.3 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From f74f2e2e26199f695ca3df94f29e9ab7cb707ea4 Mon Sep 17 00:00:00 2001 From: Paul Mackerras <paulus@xxxxxxxxx> Date: Tue, 3 Nov 2015 16:03:30 +1100 Subject: KVM: PPC: Book3S HV: Don't dynamically split core when already split From: Paul Mackerras <paulus@xxxxxxxxx> commit f74f2e2e26199f695ca3df94f29e9ab7cb707ea4 upstream. In static micro-threading modes, the dynamic micro-threading code is supposed to be disabled, because subcores can't make independent decisions about what micro-threading mode to put the core in - there is only one micro-threading mode for the whole core. The code that implements dynamic micro-threading checks for this, except that the check was missed in one case. This means that it is possible for a subcore in static 2-way micro-threading mode to try to put the core into 4-way micro-threading mode, which usually leads to stuck CPUs, spinlock lockups, and other stalls in the host. The problem was in the can_split_piggybacked_subcores() function, which should always return false if the system is in a static micro-threading mode. This fixes the problem by making can_split_piggybacked_subcores() use subcore_config_ok() for its checks, as subcore_config_ok() includes the necessary check for the static micro-threading modes. Credit to Gautham Shenoy for working out that the reason for the hangs and stalls we were seeing was that we were trying to do dynamic 4-way micro-threading while we were in static 2-way mode. Fixes: b4deba5c41e9 Signed-off-by: Paul Mackerras <paulus@xxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- arch/powerpc/kvm/book3s_hv.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/arch/powerpc/kvm/book3s_hv.c +++ b/arch/powerpc/kvm/book3s_hv.c @@ -2019,7 +2019,7 @@ static bool can_split_piggybacked_subcor return false; n_subcores += (cip->subcore_threads[sub] - 1) >> 1; } - if (n_subcores > 3 || large_sub < 0) + if (large_sub < 0 || !subcore_config_ok(n_subcores + 1, 2)) return false; /* Patches currently in stable-queue which might be from paulus@xxxxxxxxx are queue-4.3/kvm-ppc-book3s-hv-prohibit-setting-illegal-transaction-state-in-msr.patch queue-4.3/kvm-ppc-book3s-hv-don-t-dynamically-split-core-when-already-split.patch -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html