On Mon, May 13, 2019 at 09:21:01AM +0000, Nadav Amit wrote: > > On May 13, 2019, at 2:12 AM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote: > >> The other thing I was thinking of is trying to detect overlap through > >> the page-tables themselves, but we have a distinct lack of storage > >> there. > > > > We might just use some state in the pmd, there's still 2 _pt_pad_[12] in > > struct page to 'use'. So we could come up with some tlb generation > > scheme that would detect conflict. > > It is rather easy to come up with a scheme (and I did similar things) if you > flush the table while you hold the page-tables lock. But if you batch across > page-tables it becomes harder. Yeah; finding that out now. I keep finding holes :/ > Thinking about it while typing, perhaps it is simpler than I think - if you > need to flush range that runs across more than a single table, you are very > likely to flush a range of more than 33 entries, so anyhow you are likely to > do a full TLB flush. We can't rely on the 33, that x86 specific. Other architectures can have another (or no) limit on that. > So perhaps just avoiding the batching if only entries from a single table > are flushed would be enough. That's near to what Will suggested initially, just flush the entire thing when there's a conflict.
