From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.linuxfoundation.org ([140.211.169.12]:49978 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934621AbcA0SOL (ORCPT ); Wed, 27 Jan 2016 13:14:11 -0500 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Paul Mackerras Subject: [PATCH 4.3 009/157] KVM: PPC: Book3S HV: Dont dynamically split core when already split Date: Wed, 27 Jan 2016 10:11:16 -0800 Message-Id: <20160127180933.011309041@linuxfoundation.org> In-Reply-To: <20160127180932.533735338@linuxfoundation.org> References: <20160127180932.533735338@linuxfoundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-15 Sender: stable-owner@vger.kernel.org List-ID: 4.3-stable review patch. If anyone has any objections, please let me know. ------------------ From: Paul Mackerras 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 Signed-off-by: Greg Kroah-Hartman --- 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; /*