Andy Lutomirski [off-list ref] wrote:

On Wed, Jul 12, 2017 at 4:27 PM, Nadav Amit [off-list ref] wrote:

quoted

Actually, I think that based on Andy’s patches there is a relatively
reasonable solution. For each mm we will hold both a “pending_tlb_gen”
(increased under the PT-lock) and an “executed_tlb_gen”. Once
flush_tlb_mm_range finishes flushing it will use cmpxchg to update the
executed_tlb_gen to the pending_tlb_gen that was prior the flush (the
cmpxchg will ensure the TLB gen only goes forward). Then, whenever
pending_tlb_gen is different than executed_tlb_gen - a flush is needed.

Why do we need executed_tlb_gen?  We already have
cpu_tlbstate.ctxs[...].tlb_gen.  Or is the idea that executed_tlb_gen
guarantees that all cpus in mm_cpumask are at least up to date to
executed_tlb_gen?

Hm... So actually it may be enough, no? Just compare mm->context.tlb_gen
with cpu_tlbstate.ctxs[...].tlb_gen and flush if they are different?

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