On Wed, Apr 07, 2021 at 04:48:44PM +0200, Peter Zijlstra wrote: > On Tue, Apr 06, 2021 at 06:44:36PM -0700, Michel Lespinasse wrote: > > --- a/arch/x86/mm/fault.c > > +++ b/arch/x86/mm/fault.c > > @@ -1219,6 +1219,8 @@ void do_user_addr_fault(struct pt_regs *regs, > > struct mm_struct *mm; > > vm_fault_t fault; > > unsigned int flags = FAULT_FLAG_DEFAULT; > > + struct vm_area_struct pvma; > > That's 200 bytes on-stack... I suppose that's just about acceptible, but > perhaps we need a comment in struct vm_area_struct to make people aware > this things lives on-stack and size really is an issue now. Right, I agree that having the vma copy on-stack is not ideal. I think what really should be done, is to copy just the attributes of the vma that will be needed during the page fault. Things like vm_mm, vm_page_prot, vm_flags, vm_ops, vm_pgoff, vm_file, vm_private_data, vm_policy. We definitely do not need rbtree and rmap fields such as vm_prev, vm_next, vm_rb, rb_subtree_gap, shared, anon_vma_chain etc... The reason I did things this way, is because changing the entire fault handler to use attributes stored in struct vm_fault, rather than in the original vma, would be quite intrusive. I think it would be a reasonable step to consider once there is agreement on the rest of the speculative fault patch set, but it's practical doing it before then.
