On 12/11/2017 11:39 AM, Andy Lutomirski wrote: >> I thought there would be a "fast path" where we just use the normal >> clear_LDT() LDT from the cpu_entry_area and don't have to do any of >> this, but I'm missing where that happens. Do we need a check in >> (un)map_ldt_struct() for !mm->context.ldt? > I'm confused. > > if (unlikely(ldt)) { > do something slowish; > } else { > clear_LD(); > }
I was looking at the map/unmap paths. It looks to me like the cases where there is map/unmap overhead, we *are* doing checking against mm->context.ldt. It just wasn't visible from the patch context. In any case, it would be really nice to call that out if you revise these in the patch description: none of these LDT acrobatics are used in the common case. Virtually every process uses the !ldt paths which don't do any of this.