On 18 May 2006, at 21:20, Zachary Amsden wrote: >> 1. We clear FS/GS before changing TLS entries and switching LDT, as >> otherwise the hypervisor will fail to restore thread-local values on >> return to the guest kernel and we take a slow exception path. > >> @@ -647,6 +647,8 @@ struct task_struct fastcall * __switch_t >> */ >> savesegment(fs, prev->fs); >> savesegment(gs, prev->gs); >> + clearsegment(fs); >> + clearsegment(gs); >> > > Really not needed. Think about it. You can even speed up Xen. I'm > glad the native operation here is a nop, but it should be > hypervisor_clearsegment or xen_clearsegment if you really want to keep > it. Maybe you could explain in more detail? It's not needed for correctness, but it is faster for us to clear at that point. -- Keir
