kern/58381: ddb show page command crashes on invalid vm_page structures

[campbell+netbsd%mumble.net@localhost]

>Number:         58381
>Category:       kern
>Synopsis:       ddb show page command crashes on invalid vm_page structures
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sun Jun 30 11:25:01 +0000 2024
>Originator:     Taylor R Campbell
>Release:        current, 10
>Organization:
The NetBStopped in pid 0.0 (system) at  netbsd:breakpoint+0x5:   leave
>Environment:
>Description:
Quoted from diagnostics in PR kern/58366 (https://gnats.NetBSD.org/58366):

 db{0}> show page
 PAGE 0xffffffffe78c60a6:
   flags=0x6601f173<CLEAN,DIRTY,PAGEOUT,RELEASED,FAKE,ZERO,FILE,READAHEAD,FREE,MARKER,PAGER1>
   pqflags=0xf66d04d<INTENT_0,INTENT_SET,INTENT_QUEUED,PRIVATE3,WANTED>
   uobject=0x6a0f66c86f0f66c8, uanon=0x7e0f416655c8700f, offset=0xf66c97e0f4166c8

 [   1.2851297] panic: kernel diagnostic assertion "upm != UVM_PHYSSEG_TYPE_INVALID" failed: file "/home/h/netbsd/git/src/sys/uvm/uvm_page.c", line 2015 
 [   1.2851297] cpu0: Begin traceback...
 [   1.2851297] vpanic() at netbsd:vpanic+0x173
 [   1.2851297] kern_assert() at netbsd:kern_assert+0x4b
 [   1.2851297] uvm_page_lookup_freelist() at netbsd:uvm_page_lookup_freelist+0x59
 [   1.2851297] uvm_page_printit() at netbsd:uvm_page_printit+0xc1
 [   1.2851297] db_command() at netbsd:db_command+0x123
 [   1.2851297] db_command_loop() at netbsd:db_command_loop+0xa4
 [   1.2851297] db_trap() at netbsd:db_trap+0xcc
 [   1.2851297] kdb_trap() at netbsd:kdb_trap+0x106
 [   1.2851297] trap() at netbsd:trap+0x28f
 [   1.2851297] --- trap (number 4) ---
>How-To-Repeat:
Pass an address to memory that is not a fully valid struct vm_page object to show page in ddb.
>Fix:
Yes, please!