kern/59328: viomb(4) various issues

[campbell+netbsd%mumble.net@localhost]

>Number:         59328
>Category:       kern
>Synopsis:       viomb(4) various issues
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sat Apr 19 11:05:00 +0000 2025
>Originator:     Taylor R Campbell
>Release:        current
>Organization:
The NetBalloonD Foundation
>Environment:
>Description:
1. KNF violations
2. unlocked access to sc_npages, sc_actual
3. non-obvious serialization of sc_inflight
4. missing support for PAGE_SIZE > VIRTIO_PAGE_SIZE = 4096, PAGE_SIZE % VIRTIO_PAGE_SIZE == 0 -- should be easy, I expect, by just splitting each guest page into multiple host pages
5. printf -> device_printf
6. possible infinite sleep if mstohz rounds to 0
7. the following panic:

viomb0: inflating balloon from 326876 to 327400.
panic: kernel diagnostic assertion "!samepage" failed: file "/usr/src/sys/arch/x86/x86/pmap.c", line 5214
cpu5: Begin traceback...
vpanic() at netbsd:vpanic+0x171
kern_assert() at netbsd:kern_assert+0x4b
pmap_enter_ma() at netbsd:pmap_enter_ma+0xbc6
pmap_enter_default() at netbsd:pmap_enter_default+0x29
uvm_fault_internal() at netbsd:uvm_fault_internal+0x90e
trap() at netbsd:trap+0x3a6
--- trap (number 6) ---
d5e33d:
cpu5: End traceback...

8. the following panic:

[Sat Apr 19 15:37:28 EEST 2025] viomb0: inflating balloon from 314664 to 314794.
[Sat Apr 19 15:37:38 EEST 2025] viomb0: deflating balloon from 314794 to 314699.
[Sat Apr 19 15:37:47 EEST 2025] viomb0: deflating balloon from 314699 to 313638.
[Sat Apr 19 15:37:48 EEST 2025] panic: pr_phinpage_check: [socket] item 0xffff831bc1062158 not part of pool


Part (7) might be a coincidence -- no timestamps to compare; see also PR kern/56617: assertion "!samepage" failed <https://gnats.NetBSD.org/56617>, on a machine which I suspect has no viomb.

Part (8) might also be a coincidence, hard to be sure.
>How-To-Repeat:
1-6. code inspection
7-8. run rust builds in multiple VMs on a single host with 64 GB RAM
>Fix:
Yes, please!