From: Brent Cook Subject: Re: Sysupgrade on i386 vmm to current snapshot hangs on boot into upgrade kernel To: Mike Larkin Cc: Alexander Bluhm , tech@openbsd.org Date: Sun, 5 Apr 2026 19:41:23 -0500 On Sun, Apr 5, 2026 at 2:36 PM Mike Larkin wrote: > On Sun, Apr 05, 2026 at 01:08:51PM -0500, Brent Cook wrote: > > On Sun, Apr 05, 2026 at 04:58:11AM -0500, Brent Cook wrote: > > > On Tue, Mar 31, 2026 at 1:35 PM Alexander Bluhm > wrote: > > > > > > > On Tue, Mar 31, 2026 at 09:30:30AM -0700, Mike Larkin wrote: > > > > > rebuild the host kernel with HZ=1000 and see if running that makes > the > > > > problem > > > > > go away. > > > > > > > > I have option HZ=1000 in host's sys/conf/GENERIC now. It does not > help. > > > > Guest's GENERIC is unmodified. > > > > > > > > When the i386 guest boots, its GENERIC either says > > > > cpu0: AMD EPYC 73F3 16-Core Processor ("AuthenticAMD" 686-class, > 512KB L2 > > > > cache) 3.50 GHz, 19-01-01 > > > > or > > > > cpu0: AMD EPYC 73F3 16-Core Processor ("AuthenticAMD" 686-class, > 512KB L2 > > > > cache) 74 MHz, 19-01-01 > > > > > > > > > > > Same thing here, but this is a clue why RAMDISK_CD hangs but not > GENERIC > > > are hanging, at least for me. > > > > > > Adding pvclock0 allows RAMDISK_CD to boot 100% of the time in my local > vmm > > > machine. > > > > > > diff --git a/sys/arch/i386/conf/RAMDISK_CD > b/sys/arch/i386/conf/RAMDISK_CD > > > index c00f6dcbbb4..24bd4e465a9 100644 > > > --- a/sys/arch/i386/conf/RAMDISK_CD > > > +++ b/sys/arch/i386/conf/RAMDISK_CD > > > @@ -28,6 +28,7 @@ config bsd root on rd0a swap on rd0b > and > > > wd0b and sd0b > > > mainbus0 at root > > > > > > pvbus0 at mainbus0 # Paravirtual device bus > > > +pvclock0 at pvbus? # KVM/VMD paravirtual clock > > > > > > acpi0 at bios? > > > #acpitimer* at acpi? > > > > > > > > > > Ugh, that last paste was ugly, sorry. Switching mail clients: > > > > Would anyone be able to give this diff a try? It's working locally; I > > was able reliably get the i8254 to calibrate to 4GHz, and see no hangs > > either in RAMDISK_CD or when switching sysctl > > kern.timecounter.hardware=i8254. Now my i386 VMM machine can > > sysupgrade reliably > > > > The main change here is to set the timestamp right in the vcpu thread > > instead of later in the event loop in i8253_reset. Otherwise, a latch > > command issued before i8253_reset runs will be using a new start value, > > but an old stale ts value. Maybe this makes the clock_gettime in > > i8253_reset unnecessary, but I left it in. > > > > This also adjusts a couple of the register states to match that of > > Bhyve when the mode is updated or there is a latch command: > > > > > https://github.com/freebsd/freebsd-src/blob/main/sys/amd64/vmm/io/vatpit.c#L239 > > > https://github.com/freebsd/freebsd-src/blob/main/sys/amd64/vmm/io/vatpit.c#L330 > > > > Hopefully this makes sense, or if it's the wrong approach, at least > > inspires the correct fix. > > > > this makes sense to me; I think the key fix here is the resetting of last_r > to 2, indicating that 2 bytes must be read. this makes sense after a latch > and makes more sense WRT the 8253 state machine. > > The other bits may or may not be needed but they seem correct also and/or > harmless, so I'd say leave them in for consistency. > > I don't have any machines that exhibit the issue so as long as you get this > tested on some various guest OSes, ok mlarkin. (eg test linux, openbsd > amd64 > and openbsd i386, make sure nothing gets broken) > > -ml > Thanks, so far everything is looking good on Debian i386/amd64, Alpine x86_64, and the OpenBSDs. Alpine x86 32-bit is dying when booting the installer with what looks like a memory probe that isn't handled yet by vmm. vmx_handle_np_fault: unknown memory type 2 for GPA 0xc4e89a0c But I think that is a pre-existing issue. > > diff --git a/usr.sbin/vmd/i8253.c b/usr.sbin/vmd/i8253.c > > index 9e32d9382b6..091716a2f32 100644 > > --- a/usr.sbin/vmd/i8253.c > > +++ b/usr.sbin/vmd/i8253.c > > @@ -262,12 +262,14 @@ vcpu_exit_i8253(struct vm_run_params *vrp) > > ticks % > i8253_channel[sel].start; > > } else > > i8253_channel[sel].olatch = 0; > > + i8253_channel[sel].last_r = 2; > > goto ret; > > } else if (rw != TIMER_16BIT) { > > log_warnx("%s: i8253 PIT: unsupported > counter " > > "%d rw mode 0x%x selected", __func__, > > sel, (rw & TIMER_16BIT)); > > } > > + i8253_channel[sel].last_w = 0; > > i8253_channel[sel].mode = (out_data & 0xe) >> 1; > > > > goto ret; > > @@ -293,6 +295,9 @@ vcpu_exit_i8253(struct vm_run_params *vrp) > > if (i8253_channel[sel].start == 0) > > i8253_channel[sel].start = 0xffff; > > > > + clock_gettime(CLOCK_MONOTONIC, > > + &i8253_channel[sel].ts); > > + > > DPRINTF("%s: channel %d reset, mode=%d, " > > "start=%d\n", __func__, > > sel, i8253_channel[sel].mode, >