From: Paul Mackerras Date: Tue, 3 Nov 2015 05:03:30 +0000 (+1100) Subject: KVM: PPC: Book3S HV: Don't dynamically split core when already split X-Git-Tag: firefly_0821_release~176^2~705^2^2 X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=f74f2e2e26199f695ca3df94f29e9ab7cb707ea4;p=firefly-linux-kernel-4.4.55.git KVM: PPC: Book3S HV: Don't dynamically split core when already split 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 Cc: vger@stable.kernel.org # v4.3 Signed-off-by: Paul Mackerras --- diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c index 228049786888..becad3ababe3 100644 --- a/arch/powerpc/kvm/book3s_hv.c +++ b/arch/powerpc/kvm/book3s_hv.c @@ -2060,7 +2060,7 @@ static bool can_split_piggybacked_subcores(struct core_info *cip) 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; /*