On Wed, Nov 1, 2017 at 1:59 PM, Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx> wrote: > On 11/01/2017 01:31 PM, Andy Lutomirski wrote: >> On Wed, Nov 1, 2017 at 7:17 AM, Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx> wrote: >>> On 11/01/2017 01:03 AM, Andy Lutomirski wrote: >>>>> This ensures that any futuee context switches will do a full flush >>>>> of the TLB so they pick up the changes. >>>> I'm convuced. What was wrong with the old code? I guess I just don't >>>> see what the problem is that is solved by this patch. >>> >>> Instead of flushing *now* with INVPCID, this lets us flush *later* with >>> CR3. It just hijacks the code that you already have that flushes CR3 >>> when loading a new ASID by making all ASIDs look new in the future. >>> >>> We have to load CR3 anyway, so we might as well just do this flush then. >> >> Would it make more sense to put it in flush_tlb_func_common() instead? >> >> Also, I don't understand what clear_non_loaded_ctxs() is trying to do. >> It looks like it's invalidating all the other logical address spaces. >> And I don't see why you want a all_other_ctxs_invalid variable. Isn't >> the goal to mark a single ASID as needing a *user* flush the next time >> we switch to user mode using that ASID? Your code seems like it's >> going to flush a lot of *kernel* PCIDs. > > The point of the whole thing is to (relatively) efficiently flush > *kernel* TLB entries in *other* address spaces. Aha! That wasn't at all clear to me from the changelog. Can I make a totally different suggestion? Add a new function __flush_tlb_one_kernel() and use it for kernel addresses. That function should just do __flush_tlb_all() if KAISER is on. Then make sure that there are no performance-critical looks that call __flush_tlb_one_kernel() in KAISER mode. The approach you're using is quite expensive, and I suspect that just going a global flush may actually be faster. It's certainly a lot simpler. Optionally add a warning to __flush_tlb_one() if the address is a kernel address to help notice any missed conversions. Or just rename it to __flush_tlb_one_user(). --Andy -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
