>Number:         18958
>Category:       kern
>Synopsis:       uvm_loan users use kernel_object-backed VM ranges
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    kern-bug-people
>State:          open
>Class:          change-request
>Submitter-Id:   net
>Arrival-Date:   Wed Nov 06 22:10:03 PST 2002
>Closed-Date:
>Last-Modified:
>Originator:     Jason R Thorpe
>Release:        NetBSD 1.6I
>Organization:
Wasabi Systems, Inc.
>Environment:
	
	
System: NetBSD yeah-baby.shagadelic.org 1.6I NetBSD 1.6I (YEAH-BABY-XP) #11: Sun Sep 29 17:42:25 PDT 2002 thorpej@yeah-baby.shagadelic.org:/u1/netbsd/src/sys/arch/i386/compile/YEAH-BABY-XP i386
Architecture: i386
Machine: i386
>Description:
	Users of uvm_loan() tend to use uvm_km_valloc() or
	uvm_km_valloc_wait() to allocate the KVA at which
	loaned pages will be mapped.

	This is not a problem with basic functionality, but can
	cause interesting behavior in the face of other bugs, since
	a write fault will cause UVM to COW'd (overwriting the k-mapping
	with a non-k-mapping), which will cause a panic later, at some
	unrelated time.

	This was diagnosed by Chuq Silvers.

>How-To-Repeat:
	See the audit trail of kern/18809.

>Fix:
	Provide a uvm_km_*alloc() routine which creates a backed-
	by-nothing mapping?
>Release-Note:
>Audit-Trail:
>Unformatted: