powerpc/64s: Trim offlined CPUs from mm_cpumasks
When offlining a CPU, powerpc/64s does not flush TLBs, rather it just leaves the CPU set in mm_cpumasks, so it continues to receive TLBIEs to manage its TLBs. However the exit_flush_lazy_tlbs() function expects that after returning, all CPUs (except self) have flushed TLBs for that mm, in which case TLBIEL can be used for this flush. This breaks for offline CPUs because they don't get the IPI to flush their TLB. This can lead to stale translations. Fix this by clearing the CPU from mm_cpumasks, then flushing all TLBs before going offline. These offlined CPU bits stuck in the cpumask also prevents the cpumask from being trimmed back to local mode, which means continual broadcast IPIs or TLBIEs are needed for TLB flushing. This patch prevents that situation too. A cast of many were involved in working this out, but in particular Milton, Aneesh, Paul made key discoveries. Fixes: 0cef77c7 ("powerpc/64s/radix: flush remote CPUs out of single-threaded mm_cpumask") Signed-off-by: Nicholas Piggin <npiggin@gmail.com> Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Debugged-by: Milton Miller <miltonm@us.ibm.com> Debugged-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Debugged-by: Paul Mackerras <paulus@samba.org> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/20201126102530.691335-5-npiggin@gmail.com
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