On Fri, Dec 15, 2017 at 06:28:36PM -0800, Linus Torvalds wrote: > On Fri, Dec 15, 2017 at 5:25 PM, Dave Hansen <dave.hansen@xxxxxxxxx> wrote: > > > > I think the reason we needed VMA and PTE checks was the > > get_user_pages_fast() path not having a VMA. > > That is indeed the point of get_user_pages_fast(): no vma lookup, no > locking, just "do the default case as streamlined as possible". > > But part of it is also that we should fall back to the slow case if > the fast case doesn't work (eg because the page isn't there or > whatever). > > So what we could do - perhaps - is to just make get_user_pages_fast() > check whether any of the protection key bits are set, and fail for > that case. FWIW, a good description of fast path in get_user_pages_fast() is "simulate a TLB miss", the slow path being "... and go for simulated page fault if TLB miss would have escalated to #PF". Treating protection key bits as "escalate to page fault and let that deal with the checks" should be fine - page fault handler must cope with the page actually being present in page tables anyway, for obvious reasons... -- 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>
