[Bug 286819] Boot panics when KMSAN enabled with Ethernet driver

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=286819

            Bug ID: 286819
           Summary: Boot panics when KMSAN enabled with Ethernet driver
           Product: Base System
           Version: 14.2-STABLE
          Hardware: Any
                OS: Any
            Status: New
          Severity: Affects Only Me
          Priority: ---
         Component: kern
          Assignee: bugs@FreeBSD.org
          Reporter: hareshx.sankar.raj@intel.com

Boot panics when KMSAN is enabled in the kernel config.
Kernel config used is: KERNCONF=GENERIC-KMSAN

We had tested this in FBSD 14 stable branch and also on FBSD 14.2 release
branch. The issue remains the same.

Steps to reproduce:

git clone https://github.com/freebsd/freebsd-src /usr/src/
git checkout stable/14
echo "Build kernel"
cd /usr/src && make buildworld buildkernel -j`sysctl hw.ncpu | sed s'/hw.ncpu:
//'` KERNCONF=GENERIC-KMSAN

echo "Install kernel"
make installworld installkernel -j`sysctl hw.ncpu | sed s'/hw.ncpu: //'`
KERNCONF=GENERIC-KMSAN

echo "Reboot"
reboot

Kernel build and installation is successful.

Boot failed with below panic.

panic: MSan: uninitialized variable in 0xffffffff81234e16
cpuid = 48
time = 1746712489
KDB: stack backtrace:
#0 0xffffffff834a2616 at kdb_backtrace+0x166
#1 0xffffffff832ca9bf at vpanic+0x66f
#2 0xffffffff832ca34d at panic+0x1dd
#3 0xffffffff834b1ed9 at __msan_warning+0x219
#4 0xffffffff81234e16 at em_newitr+0xa66
#5 0xffffffff81275a02 at em_msix_que+0x172
#6 0xffffffff83a48b47 at iflib_fast_intr_rxtx+0xe7
#7 0xffffffff8314bfc4 at intr_event_handle+0x3e4
#8 0xffffffff84f4037b at intr_execute_handlers+0x1bb
#9 0xffffffff854a0fe0 at lapic_handle_intr+0x190
#10 0xffffffff84f81d11 at Xapic_isr1+0xe1
#11 0xffffffff84f315f5 at cpu_idle_acpi+0xf5
#12 0xffffffff84f31907 at cpu_idle+0x2d7
#13 0xffffffff8340521a at sched_idletd+0x62a
#14 0xffffffff83139496 at fork_exit+0x266
#15 0xffffffff84f81a2e at fork_trampoline+0xe

Based on initial analysis, the error is found as below.

(kgdb) list *0xffffffff81234e16
0xffffffff81234e16 is in em_newitr (/usr/src/sys/dev/e1000/if_em.c:1700).
warning: Source file is more recent than executable.
1695                                    nextlatency = itr_latency_bulk;
1696                            else if ((packets < 5) && (bytes > 512))
1697                                    nextlatency = itr_latency_low;
1698                            break;
1699                    case itr_latency_low: /* 20k ints/s */
1700                            if (bytes > 10000) {
1701                                    /* Handle TSO */
1702                                    if (bytes_packets > 8000)
1703                                            nextlatency = itr_latency_bulk;
1704                                    else if ((packets < 10) ||

The stack frame associated with the panic is happening in
/usr/src/sys/dev/e1000/if_em.c Ethernet driver.

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