On Wed, Nov 1, 2017 at 3:56 AM, Kirill A. Shutemov <kir...@shutemov.name> wrote: > On Wed, Nov 01, 2017 at 03:38:23AM -0700, Andy Lutomirski wrote: >> On Wed, Nov 1, 2017 at 3:11 AM, Kirill A. Shutemov <kir...@shutemov.name> >> wrote: >> > On Wed, Nov 01, 2017 at 01:01:45AM -0700, Andy Lutomirski wrote: >> >> On Tue, Oct 31, 2017 at 3:31 PM, Dave Hansen >> >> <dave.han...@linux.intel.com> wrote: >> >> > >> >> > Our CR4-based TLB flush currently requries global pages to be >> >> > supported *and* enabled. But, we really only need for them to be >> >> > supported. Make the code more robust by alllowing X86_CR4_PGE to >> >> > clear as well as set. >> >> > >> >> > This change was suggested by Kirill Shutemov. >> >> >> >> I may have missed something, but why would be ever have CR4.PGE off? >> > >> > This came out from me thinking on if we can disable global pages by not >> > turning on CR4.PGE instead of making _PAGE_GLOBAL zero. >> > >> > Dave decided to not take this path, but this change would make >> > __native_flush_tlb_global_irq_disabled() a bit less fragile in case >> > if the situation would change in the future. >> >> How about just adding a VM_WARN_ON_ONCE, then? > > What's wrong with xor? The function will continue to work this way even if > CR4.PGE is disabled.
That's true. OTOH, since no one is actually proposing doing that, there's an argument that people should get warned and therefore be forced to think about it.
