From b563764443a302aab197550870ca57fda65662b8 Mon Sep 17 00:00:00 2001 From: Martin Schwidefsky Date: Tue, 8 Jan 2019 12:44:57 +0100 Subject: [PATCH] s390/mm: always force a load of the primary ASCE on context switch commit a38662084c8bdb829ff486468c7ea801c13fcc34 upstream. The ASCE of an mm_struct can be modified after a task has been created, e.g. via crst_table_downgrade for a compat process. The active_mm logic to avoid the switch_mm call if the next task is a kernel thread can lead to a situation where switch_mm is called where 'prev == next' is true but 'prev->context.asce == next->context.asce' is not. This can lead to a situation where a CPU uses the outdated ASCE to run a task. The result can be a crash, endless loops and really subtle problem due to TLBs being created with an invalid ASCE. Cc: stable@kernel.org # v3.15+ Fixes: 53e857f30867 ("s390/mm,tlb: race of lazy TLB flush vs. recreation") Reported-by: Heiko Carstens Reviewed-by: Heiko Carstens Signed-off-by: Martin Schwidefsky Signed-off-by: Greg Kroah-Hartman --- arch/s390/include/asm/mmu_context.h | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-) diff --git a/arch/s390/include/asm/mmu_context.h b/arch/s390/include/asm/mmu_context.h index f1ab942..09b61d0 100644 --- a/arch/s390/include/asm/mmu_context.h +++ b/arch/s390/include/asm/mmu_context.h @@ -89,8 +89,6 @@ static inline void switch_mm(struct mm_struct *prev, struct mm_struct *next, { int cpu = smp_processor_id(); - if (prev == next) - return; S390_lowcore.user_asce = next->context.asce; cpumask_set_cpu(cpu, &next->context.cpu_attach_mask); /* Clear previous user-ASCE from CR1 and CR7 */ @@ -102,7 +100,8 @@ static inline void switch_mm(struct mm_struct *prev, struct mm_struct *next, __ctl_load(S390_lowcore.vdso_asce, 7, 7); clear_cpu_flag(CIF_ASCE_SECONDARY); } - cpumask_clear_cpu(cpu, &prev->context.cpu_attach_mask); + if (prev != next) + cpumask_clear_cpu(cpu, &prev->context.cpu_attach_mask); } #define finish_arch_post_lock_switch finish_arch_post_lock_switch -- 2.7.4