Start by moving `pgo_fault' handler outside of uvm_fault_lower(). If a page has a backing object that prefer to handler to fault itself the locking will be different, so keep it under KERNEL_LOCK() for the moment and make it separate from the rest of uvm_fault_lower().
ok? Index: uvm/uvm_fault.c =================================================================== RCS file: /cvs/src/sys/uvm/uvm_fault.c,v retrieving revision 1.115 diff -u -p -r1.115 uvm_fault.c --- uvm/uvm_fault.c 16 Feb 2021 09:10:17 -0000 1.115 +++ uvm/uvm_fault.c 16 Feb 2021 10:13:58 -0000 @@ -598,10 +598,37 @@ uvm_fault(vm_map_t orig_map, vaddr_t vad /* case 1: fault on an anon in our amap */ error = uvm_fault_upper(&ufi, &flt, anons, fault_type); } else { - /* case 2: fault on backing object or zero fill */ - KERNEL_LOCK(); - error = uvm_fault_lower(&ufi, &flt, pages, fault_type); - KERNEL_UNLOCK(); + struct uvm_object *uobj = ufi.entry->object.uvm_obj; + + /* + * if the desired page is not shadowed by the amap and + * we have a backing object, then we check to see if + * the backing object would prefer to handle the fault + * itself (rather than letting us do it with the usual + * pgo_get hook). the backing object signals this by + * providing a pgo_fault routine. + */ + if (uobj != NULL && uobj->pgops->pgo_fault != NULL) { + KERNEL_LOCK(); + error = uobj->pgops->pgo_fault(&ufi, + flt.startva, pages, flt.npages, + flt.centeridx, fault_type, flt.access_type, + PGO_LOCKED); + KERNEL_UNLOCK(); + + if (error == VM_PAGER_OK) + error = 0; + else if (error == VM_PAGER_REFAULT) + error = ERESTART; + else + error = EACCES; + } else { + /* case 2: fault on backing obj or zero fill */ + KERNEL_LOCK(); + error = uvm_fault_lower(&ufi, &flt, pages, + fault_type); + KERNEL_UNLOCK(); + } } } @@ -1054,26 +1081,6 @@ uvm_fault_lower(struct uvm_faultinfo *uf struct vm_anon *anon = NULL; vaddr_t currva; voff_t uoff; - - /* - * if the desired page is not shadowed by the amap and we have a - * backing object, then we check to see if the backing object would - * prefer to handle the fault itself (rather than letting us do it - * with the usual pgo_get hook). the backing object signals this by - * providing a pgo_fault routine. - */ - if (uobj != NULL && uobj->pgops->pgo_fault != NULL) { - result = uobj->pgops->pgo_fault(ufi, flt->startva, pages, - flt->npages, flt->centeridx, fault_type, flt->access_type, - PGO_LOCKED); - - if (result == VM_PAGER_OK) - return (0); /* pgo_fault did pmap enter */ - else if (result == VM_PAGER_REFAULT) - return ERESTART; /* try again! */ - else - return (EACCES); - } /* * now, if the desired page is not shadowed by the amap and we have