On Mon, 7 May 2018 12:00:58 +1000 Paul Mackerras <paulus@xxxxxxxxxx> wrote: > On Sun, May 06, 2018 at 05:37:25PM +1000, Nicholas Piggin wrote: > > The radix fault handler will unmap a page table if it wants to install > > a huge page there instead. It will just clear that page table entry, > > free the page, and flush the pwc. > > This is a pretty inadequate commit description. You are describing > what the code does before your patch, but you don't say why that is > bad or what your patch does and why that is better. > > In particular, I don't see how we could ever get the situation where > we are replacing a page table page with a huge page and there are any > valid leaf PTEs in (or below) that page table page. I accept that I > am leaking the page table pages but I don't see why tlbies would be > necessary. > > What scenario did you have in mind where we would need to do the full > unmap, that is, where would would find any valid leaf PTEs in a page > table page that we are replacing? I actually wasn't 100% sure if a fault could ever try to install a 64k pte when another could install a 2MB (without an interleaving invalidation). If that's not required I can take it out of this patch, I'd like to add it back in a subsequent change to do proper range invalidates that don't leave these stale page tables around for the fault path to clean up, but that discussion can be left until then. Thanks, Nick -- To unsubscribe from this list: send the line "unsubscribe kvm-ppc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
