From f6aa37c51ec0d053ee34c235bfe0e666618a3baf Mon Sep 17 00:00:00 2001 From: Laurent Dufour Date: Mon, 14 Nov 2022 17:01:50 +0100 Subject: [PATCH] powerpc/pseries: unregister VPA when hot unplugging a CPU The VPA should unregister when offlining a CPU. Otherwise there could be a short window where 2 CPUs could share the same VPA. This happens because the hypervisor is still keeping the VPA attached to the vCPU even if it became offline. Here is a potential situation: 1. remove proc A, 2. add proc B. If proc B gets proc A's place in cpu_present_mask, then it registers proc A's VPAs. 3. If proc B is then re-added to the LP, its threads are sharing VPAs with proc A briefly as they come online. As the hypervisor may check for the VPA's yield_count field oddity, it may detect an unexpected value and kill the LPAR. Suggested-by: Nathan Lynch Signed-off-by: Laurent Dufour Reviewed-by: Nathan Lynch [mpe: s/cpu_present_map/cpu_present_mask/ in change log] Signed-off-by: Michael Ellerman Link: https://lore.kernel.org/r/20221114160150.13554-1-ldufour@linux.ibm.com --- arch/powerpc/platforms/pseries/hotplug-cpu.c | 1 + 1 file changed, 1 insertion(+) diff --git a/arch/powerpc/platforms/pseries/hotplug-cpu.c b/arch/powerpc/platforms/pseries/hotplug-cpu.c index e0a7ac5db15d..090ae5a1e0f5 100644 --- a/arch/powerpc/platforms/pseries/hotplug-cpu.c +++ b/arch/powerpc/platforms/pseries/hotplug-cpu.c @@ -70,6 +70,7 @@ static void pseries_cpu_offline_self(void) xics_teardown_cpu(); unregister_slb_shadow(hwcpu); + unregister_vpa(hwcpu); rtas_stop_self(); /* Should never get here... */