On Thu, Nov 21, 2024 at 07:07:44AM -0800, Dave Hansen wrote: > On 11/21/24 03:12, Peter Zijlstra wrote: > >> I see e.g. ds_clear_cea() clears PTEs that can have the _PAGE_GLOBAL flag, > >> and it correctly uses the non-deferrable flush_tlb_kernel_range(). > > > > I always forget what we use global pages for, dhansen might know, but > > let me try and have a look. > > > > I *think* we only have GLOBAL on kernel text, and that only sometimes. > > I think you're remembering how _PAGE_GLOBAL gets used when KPTI is in play. Yah, I suppose I am. That was the last time I had a good look at this stuff :-) > Ignoring KPTI for a sec... We use _PAGE_GLOBAL for all kernel mappings. > Before PCIDs, global mappings let the kernel TLB entries live across CR3 > writes. When PCIDs are in play, global mappings let two different ASIDs > share TLB entries. Hurmph.. bah. That means we do need that horrible CR4 dance :/
