4.20-stable review patch. If anyone has any objections, please let me know.
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From: Martin Schwidefsky schwidefsky@de.ibm.com
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This can lead to a situation where a CPU uses the outdated ASCE to run a task.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 heiko.carstens@de.ibm.com Reviewed-by: Heiko Carstens heiko.carstens@de.ibm.com Signed-off-by: Martin Schwidefsky schwidefsky@de.ibm.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/s390/include/asm/mmu_context.h | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-)
--- a/arch/s390/include/asm/mmu_context.h +++ b/arch/s390/include/asm/mmu_context.h @@ -90,8 +90,6 @@ static inline void switch_mm(struct mm_s { 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 */ @@ -103,7 +101,8 @@ static inline void switch_mm(struct mm_s __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