Re: install/49470

[Andrius V <vezhlys%gmail.com@localhost>]

The following reply was made to PR port-amd64/49470; it has been noted by GNATS.

From: Andrius V <vezhlys%gmail.com@localhost>
To: gnats-bugs%netbsd.org@localhost
Cc: 
Subject: Re: install/49470
Date: Mon, 22 Jul 2024 09:40:20 +0300

 Hi,
 
 On Tue, Jul 2, 2024 at 1:53=E2=80=AFPM Andrius V <vezhlys%gmail.com@localhost> wrote:
 >
 > The following reply was made to PR port-amd64/49470; it has been noted by=
  GNATS.
 >
 > From: Andrius V <vezhlys%gmail.com@localhost>
 > To: gnats-bugs%netbsd.org@localhost
 > Cc: tuotila%gmx.com@localhost, kazbloxmc%gmail.com@localhost
 > Subject: Re: install/49470
 > Date: Tue, 2 Jul 2024 13:33:53 +0300
 >
 >  It is reproducible on Biostar Viotech 3100+ with VIA C7-D CPU on the
 >  install image. Same install kernel does boot on the installed system.
 >  As another workaround, reducing ACPI version to v2 (from v3) in the
 >  BIOS also makes system boot from the install image. The issue seems to
 >  be introduced between before NetBSD 7, since NetBSD 6.x releases still
 >  boot.  Will try to investigate a bit if I can find something.
 >
 
 Initial analysis:
 The issue seems to have started with switch to gcc 4.8
 (https://github.com/NetBSD/src/commit/ad33dd774c2fe8beb41c96d1d29aef4ebce3f=
 5cb
 and https://github.com/NetBSD/src/commit/f8008b9438a836d85ee0b14cb56ee82966=
 fd8216).
 
 It prints this log and reboots:
 booting hd0a:netbsd (howto 0xa0000)
 22005524+593000+742296 [1003696+1091430+13604]=3D0x1846608
 [   1.0000000] cpu_rng: via
 [   1.0000000] pmap_kenter_pa: mapping already present
 
 It reboots on memcpy() call, I assume because both source and
 destination pointers are NULL (printed them out for testing):
 https://github.com/NetBSD/src/blob/ee4113b4927055cea72b04191634f65fc3bf3580=
 /sys/kern/subr_kcpuset.c#L351
 which in turn was called from pmap_tlb_shootdown() ->
 kcpuset_copy(ci->ci_tlb_cpuset, kcpuset_running)
 https://github.com/NetBSD/src/blob/ee4113b4927055cea72b04191634f65fc3bf3580=
 /sys/arch/x86/x86/x86_tlb.c#L289
 And finally shootdown was called from kenter funciton -
 pmap_kenter_pa() in the "/* This should not happen. */" path:
 https://github.com/NetBSD/src/blob/ee4113b4927055cea72b04191634f65fc3bf3580=
 /sys/arch/x86/x86/pmap.c#L1056
 
 This typically happens if arguments are passed to the boot command
 (e.g. boot netbsd or boot netbsd -vx), but boots properly without
 passing the kernel (e.g. boot or boot -vx), but it's not always the
 case for all my setups (it is an opposite in one setup, where system
 is installed in sd media (a bit older release)). If it boots, it
 doesn't enter the unexpected path in kenter function.
 
 It happens only if ACPI version is set to v3.0 in BIOS. It boots in
 all combinations I have tried if ACPI version is set to v2.0 or v1.0.
 
 I see it is likely at least two issues:
 No checks before memcpy() or kcpuset_copy() that values are null and I
 guess some additional asserts are needed here as a band-aid before one
 of these calls?
 
 Another issue is the root cause why this unintended path is taken,
 somehow related to ACPI version and boot command. Is it also some kind
 of undesirable optimization, maybe CPU bug or something else, I still
 need to understand.
 
 Regards,
 Andrius V