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fix timer emulation-related VM hangs

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This fixes state machine issues that resulted in hangs with OpenBSD-i386 VMs
when using the i8254 hardware timecounter with vmm. This also manifested in
incorrect i8254 calibration (wrong CPU speed in dmesg).

tested with Debian 12 amd64, i386
Apine Linux 3.23 x86 (with 4GB memory), x86_64
OpenBSD 7.9 beta amd64, i386

ok mlarkin@
This commit is contained in:
bcook
2026-04-07 03:21:10 +00:00
parent 75447644f5
commit f96d31f38e
1 changed files with 6 additions and 1 deletions
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7
usr.sbin/vmd/i8253.c
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@@ -1,4 +1,4 @@
/* $OpenBSD: i8253.c,v 1.45 2025/12/02 02:31:10 dv Exp $ */
/* $OpenBSD: i8253.c,v 1.46 2026/04/07 03:21:10 bcook Exp $ */
/*
* Copyright (c) 2016 Mike Larkin <mlarkin@openbsd.org>
*
@@ -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 = 1;
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,