port-xen/60466: DOM0 panic as NR_PIRQS is too low with many CPUs

["netbsd%precedence.co.uk@localhost via gnats" <gnats-admin%NetBSD.org@localhost>]

>Number:         60466
>Category:       port-xen
>Synopsis:       DOM0 panic as NR_PIRQS is too low with many CPUs
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    port-xen-maintainer
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Mon Jul 20 09:55:00 +0000 2026
>Originator:     Stephen Borrill
>Release:        11.0_RC6
>Organization:
>Environment:
NetBSD dom0 11.0_RC6 NetBSD 11.0_RC6 (XEN3_DOM0) #0: Thu Jul  9 08:20:25 UTC 2026  mkrepro%mkrepro.NetBSD.org@localhost:/usr/src/sys/arch/xen/compile/XEN3_DOM0 amd64
>Description:
Here is a dmesg extract from booting 11.0_RC6 XEN3_DOM0 (2x 6C Xeon with HT) with Xen 4.20 on an IBM x3550M4:

ixg0 at pci3 dev 0 function 0: Intel(R) PRO/10GbE PCI-Express Network Driver, Version - 4.0.1-k
ixg0: device 82599EB
ixg0: ETrackID 800006c7
ixg0: PBA number G70815-008
panic: pirq 4991 out of bound, increase NR_PIRQS
cpu0: Begin traceback...
vpanic() at netbsd:vpanic+0x161
panic() at netbsd:panic+0x3c
bind_pirq_to_evtch() at netbsd:bind_pirq_to_evtch+0x93
intr_establish_xname() at netbsd:intr_establish_xname+0xe1
x86_pci_msix_establish() at netbsd:x86_pci_msix_establish+0x6d
ixgbe_attach() at netbsd:ixgbe_attach+0x1dd6

A full dmesg when dom0_max_vcpus=1 is as follows:

NetBSD 11.0_RC6 (XEN3_DOM0) #0: Thu Jul  9 08:20:25 UTC 2026
	mkrepro%mkrepro.NetBSD.org@localhost:/usr/src/sys/arch/xen/compile/XEN3_DOM0
total memory = 1024 MB
avail memory = 968 MB
timecounter: Timecounters tick every 10.000 msec
Kernelized RAIDframe activated
mainbus0 (root)
ACPI: RSDP 0x00000000000FDFD0 000024 (v02 IBM   )
ACPI: XSDT 0x000000006AE381C0 0000C4 (v01 IBM    SERMEGAL 00000000      01000013)
ACPI: FACP 0x000000006A079000 0000F4 (v04 IBM    SERMEGAL 00000000 MSFT 01000019)
ACPI: DSDT 0x0000000069F97000 004F2D (v01 INTEL  TIANO    00000003 MSFT 01000013)
ACPI: FACS 0x000000007E903000 000040
ACPI: TCPA 0x000000006AC12000 000064 (v00                 00000000      00000000)
ACPI: ERST 0x000000006A07A000 000230 (v01 IBM    SERMEGAL 00000001 MSFT 0100001B)
ACPI: HEST 0x000000006A076000 0001A4 (v01 IBM    SERMEGAL 00000001 MSFT 0100001E)
ACPI: HPET 0x000000006A075000 000038 (v01 IBM    SERMEGAL 00000001 MSFT 01000017)
ACPI: APIC 0x0000000069FA9000 00012A (v03 IBM    SERMEGAL 00000000 MSFT 01000014)
ACPI: MCFG 0x0000000069FAB000 00003C (v01 IBM    SERMEGAL 00000001 MSFT 01000018)
ACPI: OEM0 0x0000000069FAA000 000268 (v03 IBM    XSECSRAT 00000100 MSFT 01000022)
ACPI: OEM1 0x0000000069FA8000 000030 (v01 IBM    IBMERROR 00000001 MSFT 01000013)
ACPI: SLIT 0x0000000069FA6000 000030 (v01 IBM    SERMEGAL 00000001 MSFT 01000020)
ACPI: SRAT 0x0000000069FA5000 000228 (v03 IBM    SERMEGAL 00000001 MSFT 0100001A)
ACPI: SLIC 0x0000000069FA4000 000176 (v01 IBM    SERMEGAL 00000000 MSFT 0100001F)
ACPI: SSDT 0x0000000069F94000 000527 (v02 IBM    CPUSCOPE 00004000 MSFT 01000016)
ACPI: SSDT 0x0000000069F7B000 00052E (v02 IBM    CPUWYVRN 00004000 MSFT 01000016)
ACPI: SSDT 0x0000000069F6C000 006474 (v02 IBM    PSTATEPM 00004000 MSFT 01000016)
ACPI: SSDT 0x0000000069F95000 000ECA (v02 IBM    CPUCSTAT 00004000 MSFT 01000016)
ACPI: SSDT 0x0000000069F7A000 000214 (v02 IBM    WYVRNDEV 00004000 MSFT 01000016)
ACPI: SSDT 0x0000000069F79000 00009E (v02 IBM    WYVRNGPE 00004000 MSFT 01000016)
ACPI: SSDT 0x0000000069F76000 0006EF (v02 IBM    CPUNOTFY 00004000 MSFT 01000016)
ACPI: RMAD 0x00000000672F1000 000158 (v01 IBM    SERMEGAL 00000001 MSFT 01000021)
ACPI: 8 ACPI AML tables successfully acquired and loaded
ioapic0 at mainbus0 apid 8: pa 0xfec00000, version 0x20, 24 pins
ioapic1 at mainbus0 apid 9: pa 0xfec01000, version 0x20, 24 pins
ioapic2 at mainbus0 apid 10: pa 0xfec40000, version 0x20, 24 pins
cpu0 at mainbus0 apid 0
cpu1 at mainbus0 apid 2
cpu2 at mainbus0 apid 4
cpu3 at mainbus0 apid 6
cpu4 at mainbus0 apid 8
cpu5 at mainbus0 apid 10
cpu6 at mainbus0 apid 32
cpu7 at mainbus0 apid 34
cpu8 at mainbus0 apid 36
cpu9 at mainbus0 apid 38
cpu10 at mainbus0 apid 40
cpu11 at mainbus0 apid 42
cpu12 at mainbus0 apid 1
cpu13 at mainbus0 apid 3
cpu14 at mainbus0 apid 5
cpu15 at mainbus0 apid 7
cpu16 at mainbus0 apid 9
cpu17 at mainbus0 apid 11
cpu18 at mainbus0 apid 33
cpu19 at mainbus0 apid 35
cpu20 at mainbus0 apid 37
cpu21 at mainbus0 apid 39
cpu22 at mainbus0 apid 41
cpu23 at mainbus0 apid 43
ipmi0 at mainbus0
hypervisor0 at mainbus0: Xen version 4.20.4-pre_20260610
hypervisor0: features:  mmu_pt_update_preserve_ad highmem_assist gnttab_map_avail_bits
VIRQ_DEBUG interrupt using event channel 1
vcpu0 at hypervisor0
vcpu0: Intel(R) Xeon(R) CPU E5-2620 0 @ 2.00GHz, id 0x206d7
vcpu0: node 0, package 0, core 0, smt 0
xenbus0 at hypervisor0: Xen Virtual Bus Interface
xencons0 at hypervisor0: Xen Virtual Console Driver
acpi0 at hypervisor0: Intel ACPICA 20241212
acpi0: X/RSDT: OemId <IBM   ,SERMEGAL,00000000>, AslId <    ,01000013>
acpi0: autoconfiguration error: invalid PCI address for DFX1
acpi0: autoconfiguration error: invalid PCI address for DFX2
mpacpi: PCI bus 129 int routing already done!
acpi0: MCFG: no valid segments found
acpi0: SCI interrupting at int 9
acpi0: fixed power button present
timecounter: Timecounter "ACPI-Safe" frequency 3579545 Hz quality 900
hpet0 at acpi0: high precision event timer (mem 0xfed00000-0xfed00400)
timecounter: Timecounter "hpet0" frequency 14318180 Hz quality 2000
APIC (PNP0003) at acpi0 not configured
attimer1 at acpi0 (TMR, PNP0100): io 0x40-0x43,0x50-0x53 irq 0
pcppi1 at acpi0 (SPKR, PNP0800): io 0x61
spkr0 at pcppi1: PC Speaker
wsbell at spkr0 not configured
midi0 at pcppi1: PC speaker
UAR1 (PNP0501) at acpi0 not configured
UAR2 (PNP0501) at acpi0 not configured
tpm0 at acpi0 (TPM, PNP0C31): io 0x4e-0x4f,0x820-0x82b mem 0xfed40000-0xfed44fff
tpm0: device 0x00fe1050 rev 0x47
ACPI: Enabled 2 GPEs in block 00 to 3F
attimer1: attached to pcppi1
pci0 at hypervisor0 bus 0: configuration mode 1
pci0: i/o space, memory space enabled
pchb0 at pci0 dev 0 function 0: Intel E5 Host (rev. 0x07)
ppb0 at pci0 dev 1 function 0: Intel E5 PCIe x8 or x4 (rev. 0x07)
ppb0: PCI Express capability version 2 <Root Port of PCI-E Root Complex> x8 @ 8.0GT/s
pci1 at ppb0 bus 12
pci1: i/o space, memory space enabled
ppb1 at pci0 dev 2 function 0: Intel E5 PCIe x16, x8 or x4 (rev. 0x07)
ppb1: PCI Express capability version 2 <Root Port of PCI-E Root Complex> x16 @ 8.0GT/s
pci2 at ppb1 bus 17
pci2: i/o space, memory space enabled
ppb2 at pci0 dev 3 function 0: Intel E5 PCIe x16, x8 or x4 (rev. 0x07)
ppb2: PCI Express capability version 2 <Root Port of PCI-E Root Complex> x8 @ 8.0GT/s
ppb2: link is x8 @ 5.0GT/s
pci3 at ppb2 bus 22
pci3: i/o space, memory space enabled
ixg0 at pci3 dev 0 function 0: Intel(R) PRO/10GbE PCI-Express Network Driver, Version - 4.0.1-k
ixg0: device 82599EB
ixg0: ETrackID 800006c7
ixg0: PBA number G70815-008
ixg0: interrupting at msi0 vec 0
ixg0: Ethernet address a0:36:9f:51:12:f4
ixg0: PCI Express Bus: Speed 5.0GT/s Width x8
ixg0: feature cap 0x1780<LEGACY_TX,FDIR,MSI,MSIX,LEGACY_IRQ>
ixg0: feature ena 0x200<MSI>
ixg0: device cap 0xfffd<ALLOW_ANY_SFP,WOL_PORT0_1,WOL_PORT0,NO_CROSSTALK_WR>
ixg1 at pci3 dev 0 function 1: Intel(R) PRO/10GbE PCI-Express Network Driver, Version - 4.0.1-k
ixg1: device 82599EB
ixg1: ETrackID 800006c7
ixg1: PBA number G70815-008
ixg1: interrupting at msi1 vec 0
ixg1: Ethernet address a0:36:9f:51:12:f5
ixg1: PCI Express Bus: Speed 5.0GT/s Width x8
ixg1: feature cap 0x1780<LEGACY_TX,FDIR,MSI,MSIX,LEGACY_IRQ>
ixg1: feature ena 0x200<MSI>
ixg1: device cap 0xfffd<ALLOW_ANY_SFP,WOL_PORT0_1,WOL_PORT0,NO_CROSSTALK_WR>
ppb3 at pci0 dev 3 function 2: Intel E5 PCIe x16, x8 or x4 (rev. 0x07)
ppb3: PCI Express capability version 2 <Root Port of PCI-E Root Complex> x8 @ 8.0GT/s
pci4 at ppb3 bus 27
pci4: i/o space, memory space enabled
mfii0 at pci4 dev 0 function 0: "ServeRAID M5110", firmware 23.34.0-0023, 512MB cache
mfii0: interrupting at msix2 vec 0
mfii0: Max 256 VD support
scsibus0 at mfii0: 64 targets, 8 luns per target
Intel E5 DMA (miscellaneous system, revision 0x07) at pci0 dev 4 function 0 not configured
Intel E5 DMA (miscellaneous system, revision 0x07) at pci0 dev 4 function 1 not configured
Intel E5 DMA (miscellaneous system, revision 0x07) at pci0 dev 4 function 2 not configured
Intel E5 DMA (miscellaneous system, revision 0x07) at pci0 dev 4 function 3 not configured
Intel E5 DMA (miscellaneous system, revision 0x07) at pci0 dev 4 function 4 not configured
Intel E5 DMA (miscellaneous system, revision 0x07) at pci0 dev 4 function 5 not configured
Intel E5 DMA (miscellaneous system, revision 0x07) at pci0 dev 4 function 6 not configured
Intel E5 DMA (miscellaneous system, revision 0x07) at pci0 dev 4 function 7 not configured
Intel E5 Address Map (miscellaneous system, revision 0x07) at pci0 dev 5 function 0 not configured
Intel E5 Error Reporting (miscellaneous system, revision 0x07) at pci0 dev 5 function 2 not configured
ppb4 at pci0 dev 17 function 0: Intel C600 Virtual PCIe (rev. 0x06)
ppb4: PCI Express capability version 2 <Root Port of PCI-E Root Complex> x1 @ 2.5GT/s
pci5 at ppb4 bus 32
pci5: i/o space, memory space enabled
ehci0 at pci0 dev 26 function 0: Intel C600 USB (rev. 0x06)
ehci0: 64-bit DMA
ehci0: interrupting at ioapic0 pin 19
ehci0: EHCI version 1.0
ehci0: Using DMA subregion for control data structures
usb0 at ehci0: USB revision 2.0
ppb5 at pci0 dev 28 function 0: Intel C600/X79 PCIe (rev. 0xb6)
ppb5: PCI Express capability version 2 <Root Port of PCI-E Root Complex> x4 @ 5.0GT/s
pci6 at ppb5 bus 6
pci6: i/o space, memory space enabled
wm0 at pci6 dev 0 function 0, 64-bit DMA: I350 Gigabit Network Connection (rev. 0x01)
wm0: interrupting at msi3 vec 0
wm0: PCI-Express bus
wm0: 16384 words (16 address bits) SPI EEPROM, version 1.63, Image Unique ID 800009fa
wm0: RX packet buffer size: 36KB
wm0: Ethernet address 40:f2:e9:f1:b7:02
wm0: Copper
wm0: 0xc0674040<SPI,PCIE,NEWQUEUE,ASF_FIRM,ARC_SUBSYS,WOL,EEE,CRC_STRIP,DELAY_LINKUP>
ihphy0 at wm0 phy 1: I350 10/100/1000 media interface, rev. 1
ihphy0: 10baseT, 10baseT-FDX, 100baseTX, 100baseTX-FDX, 1000baseT, 1000baseT-FDX, auto
wm1 at pci6 dev 0 function 1, 64-bit DMA: I350 Gigabit Network Connection (rev. 0x01)
wm1: interrupting at msi4 vec 0
wm1: PCI-Express bus
wm1: 16384 words (16 address bits) SPI EEPROM, version 1.63, Image Unique ID 800009fa
wm1: RX packet buffer size: 36KB
wm1: Ethernet address 40:f2:e9:f1:b7:03
wm1: Copper
wm1: 0xc0674040<SPI,PCIE,NEWQUEUE,ASF_FIRM,ARC_SUBSYS,WOL,EEE,CRC_STRIP,DELAY_LINKUP>
ihphy1 at wm1 phy 1: I350 10/100/1000 media interface, rev. 1
ihphy1: 10baseT, 10baseT-FDX, 100baseTX, 100baseTX-FDX, 1000baseT, 1000baseT-FDX, auto
wm2 at pci6 dev 0 function 2, 64-bit DMA: I350 Gigabit Network Connection (rev. 0x01)
wm2: interrupting at msi5 vec 0
wm2: PCI-Express bus
wm2: 16384 words (16 address bits) SPI EEPROM, version 1.63, Image Unique ID 800009fa
wm2: RX packet buffer size: 36KB
wm2: Ethernet address 40:f2:e9:f1:b7:04
wm2: Copper
wm2: 0xc0674040<SPI,PCIE,NEWQUEUE,ASF_FIRM,ARC_SUBSYS,WOL,EEE,CRC_STRIP,DELAY_LINKUP>
ihphy2 at wm2 phy 1: I350 10/100/1000 media interface, rev. 1
ihphy2: 10baseT, 10baseT-FDX, 100baseTX, 100baseTX-FDX, 1000baseT, 1000baseT-FDX, auto
wm3 at pci6 dev 0 function 3, 64-bit DMA: I350 Gigabit Network Connection (rev. 0x01)
wm3: interrupting at msi6 vec 0
wm3: PCI-Express bus
wm3: 16384 words (16 address bits) SPI EEPROM, version 1.63, Image Unique ID 800009fa
wm3: RX packet buffer size: 36KB
wm3: Ethernet address 40:f2:e9:f1:b7:05
wm3: Copper
wm3: 0xc0674040<SPI,PCIE,NEWQUEUE,ASF_FIRM,ARC_SUBSYS,WOL,EEE,CRC_STRIP,DELAY_LINKUP>
ihphy3 at wm3 phy 1: I350 10/100/1000 media interface, rev. 1
ihphy3: 10baseT, 10baseT-FDX, 100baseTX, 100baseTX-FDX, 1000baseT, 1000baseT-FDX, auto
ppb6 at pci0 dev 28 function 7: Intel C600/X79 PCIe (rev. 0xb6)
ppb6: PCI Express capability version 2 <Root Port of PCI-E Root Complex> x1 @ 5.0GT/s
ppb6: link is x1 @ 2.5GT/s
pci7 at ppb6 bus 1
pci7: i/o space, memory space enabled
ppb7 at pci7 dev 0 function 0: Renesas Technologies SH7757 PCIe Switch [PS] (rev. 0x00)
ppb7: PCI Express capability version 2 <Upstream Port of PCI-E Switch>
pci8 at ppb7 bus 2
pci8: i/o space, memory space enabled
ppb8 at pci8 dev 0 function 0: Renesas Technologies SH7757 PCIe Switch [PS] (rev. 0x00)
ppb8: PCI Express capability version 2 <Downstream Port of PCI-E Switch> x1 @ 2.5GT/s
pci9 at ppb8 bus 3
pci9: i/o space, memory space enabled
ppb9 at pci9 dev 0 function 0: Renesas Technologies SH7757 PCIe-PCI Bridge [PPB] (rev. 0x00)
ppb9: PCI Express capability version 2 <PCI-E to PCI/PCI-X Bridge>
pci10 at ppb9 bus 4
pci10: i/o space, memory space enabled
vga0 at pci10 dev 0 function 0: Matrox product 0534 (rev. 0x00)
wsdisplay0 at vga0 kbdmux 1: console (80x25, vt100 emulation)
wsmux1: connecting to wsdisplay0
drm at vga0 not configured
ppb10 at pci8 dev 1 function 0: Renesas Technologies SH7757 PCIe Switch [PS] (rev. 0x00)
ppb10: PCI Express capability version 2 <Downstream Port of PCI-E Switch> x1 @ 2.5GT/s
pci11 at ppb10 bus 5
pci11: i/o space, memory space enabled
ehci1 at pci0 dev 29 function 0: Intel C600 USB (rev. 0x06)
ehci1: 64-bit DMA
ehci1: interrupting at ioapic0 pin 23
ehci1: EHCI version 1.0
ehci1: Using DMA subregion for control data structures
usb1 at ehci1: USB revision 2.0
ppb11 at pci0 dev 30 function 0: Intel 82801BA Hub-PCI Bridge (rev. 0xa6)
pci12 at ppb11 bus 33
pci12: i/o space, memory space enabled
ichlpcib0 at pci0 dev 31 function 0: Intel C600 LPC (rev. 0x06)
timecounter: Timecounter "ichlpcib0" frequency 3579545 Hz quality 1000
ichlpcib0: 24-bit timer
tco0 at ichlpcib0: TCO (watchdog) timer configured.
tco0: autoconfiguration error: TCO timer reboot disabled by hardware; hope SMBIOS properly handles it.
tco0: Min/Max interval 1/367 seconds
ahcisata0 at pci0 dev 31 function 2: Intel C600/X79 AHCI (rev. 0x06)
ahcisata0: 64-bit DMA
ahcisata0: AHCI revision 1.30, 6 ports, 32 slots, CAP 0xe310ff45<EMS,PSC,SSC,PMD,ISS=0x1=Gen1,SCLO,SAL,SSNTF,SNCQ,S64A>
ahcisata0: interrupting at msi7 vec 0
atabus0 at ahcisata0 channel 0
ichsmb0 at pci0 dev 31 function 3: Intel C600 SMBus Controller (rev. 0x06)
ichsmb0: interrupting at ioapic0 pin 11
iic0 at ichsmb0: I2C bus
isa0 at ichlpcib0
com1 at isa0 port 0x2f8-0x2ff irq 3: ns16550a, 16-byte FIFO
pckbc0 at isa0 port 0x60-0x64
pckbd0 at pckbc0 (kbd slot)
pckbc0: using irq 1 for kbd slot
wskbd0 at pckbd0: console keyboard, using wsdisplay0
pci13 at hypervisor0 bus 128
pci13: i/o space, memory space enabled
ppb12 at pci13 dev 0 function 0: Intel E5 PCIe x4 (DMI2 Mode) (rev. 0x07)
ppb12: PCI Express capability version 2 <Root Port of PCI-E Root Complex> x4 @ 5.0GT/s
pci14 at ppb12 bus 129
pci14: i/o space, memory space enabled
ppb13 at pci13 dev 2 function 0: Intel E5 PCIe x16, x8 or x4 (rev. 0x07)
ppb13: PCI Express capability version 2 <Root Port of PCI-E Root Complex> x16 @ 5.0GT/s
pci15 at ppb13 bus 134
pci15: i/o space, memory space enabled
Intel E5 DMA (miscellaneous system, revision 0x07) at pci13 dev 4 function 0 not configured
Intel E5 DMA (miscellaneous system, revision 0x07) at pci13 dev 4 function 1 not configured
Intel E5 DMA (miscellaneous system, revision 0x07) at pci13 dev 4 function 2 not configured
Intel E5 DMA (miscellaneous system, revision 0x07) at pci13 dev 4 function 3 not configured
Intel E5 DMA (miscellaneous system, revision 0x07) at pci13 dev 4 function 4 not configured
Intel E5 DMA (miscellaneous system, revision 0x07) at pci13 dev 4 function 5 not configured
Intel E5 DMA (miscellaneous system, revision 0x07) at pci13 dev 4 function 6 not configured
Intel E5 DMA (miscellaneous system, revision 0x07) at pci13 dev 4 function 7 not configured
Intel E5 Address Map (miscellaneous system, revision 0x07) at pci13 dev 5 function 0 not configured
Intel E5 Error Reporting (miscellaneous system, revision 0x07) at pci13 dev 5 function 2 not configured
WARNING: system needs entropy for security; see entropy(7)
timecounter: Timecounter "xen_system_time" frequency 1000000000 Hz quality 10000
Xen vcpu0 clock: using event channel 17
timecounter: Timecounter "clockinterrupt" frequency 100 Hz quality 0
xenbus0: using event channel 18
scsibus0: waiting 2 seconds for devices to settle...
mfii0: physical disk inserted id 18 enclosure 252
mfii0: physical disk inserted id 21 enclosure 252
IPsec: Initialized Security Association Processing.
mfii0: physical disk inserted id 22 enclosure 252
mfii0: physical disk inserted id 23 enclosure 252
mfii0: physical disk inserted id 24 enclosure 252
mfii0: physical disk inserted id 25 enclosure 252
uhub0 at usb0: NetBSD (0x0000) EHCI root hub (0x0000), class 9/0, rev 2.00/1.00, addr 1
uhub0: 3 ports with 3 removable, self powered
uhub1 at usb1: NetBSD (0x0000) EHCI root hub (0x0000), class 9/0, rev 2.00/1.00, addr 1
uhub1: 3 ports with 3 removable, self powered
entropy: ready
ahcisata0 port 0: device present, speed: 1.5Gb/s
uhub2 at uhub0 port 1: vendor 8087 (0x8087) product 0024 (0x0024), class 9/0, rev 2.00/0.00, addr 2
uhub2: single transaction translator
uhub3 at uhub1 port 1: vendor 8087 (0x8087) product 0024 (0x0024), class 9/0, rev 2.00/0.00, addr 2
uhub3: single transaction translator
uhub2: 6 ports with 6 removable, self powered
uhub3: 8 ports with 8 removable, self powered
atapibus0 at atabus0: 1 targets
cd0 at atapibus0 drive 0: <IBM SATA DEVICE 81Y3657, M1CC7JA5641, IB02> cdrom removable
cd0: drive supports PIO mode 4, DMA mode 2, Ultra-DMA mode 2 (Ultra/33)
cd0(ahcisata0:0:0): using PIO mode 4, DMA mode 2, Ultra-DMA mode 2 (Ultra/33) (using DMA)
uhub4 at uhub3 port 1: no manufacturer (0x0624) Gadget USB HUB (0x0248), class 9/0, rev 2.00/0.00, addr 3
uhub4: 6 ports with 6 removable, self powered
uhidev0 at uhub2 port 4 configuration 1 interface 0
uhidev0: Logitech (0x046d) USB Keyboard (0xc31c), rev 1.10/64.00, addr 3, iclass 3/1
ukbd0 at uhidev0
wskbd1 at ukbd0 mux 1
wskbd1: connecting to wsdisplay0
uhidev1 at uhub2 port 4 configuration 1 interface 1
uhidev1: Logitech (0x046d) USB Keyboard (0xc31c), rev 1.10/64.00, addr 3, iclass 3/0
uhidev1: 3 report ids
uhid0 at uhidev1 reportid 1: input=1, output=0, feature=0
uhid1 at uhidev1 reportid 2: input=1, output=0, feature=0
uhid2 at uhidev1 reportid 3: input=3, output=0, feature=0
sd0 at scsibus0 target 0 lun 0: <IBM, ServeRAID M5110, 3.46> disk fixed
sd0: fabricating a geometry
sd0: 68664 MB, 68664 cyl, 64 head, 32 sec, 512 bytes/sect x 140623872 sectors
sd0: fabricating a geometry
sd0: GPT GUID: f55f9022-dc93-4855-95e2-af345a382b08
dk0 at sd0: "c8a6467f-9e18-43d3-9c83-582afc3f7fe0", 132235136 blocks at 64, type: ffs
dk1 at sd0: "25cdf2e7-00af-45fb-9269-1e40f6b7d74a", 8388608 blocks at 132235200, type: swap
sd0: tagged queueing
sd1 at scsibus0 target 1 lun 0: <IBM, ServeRAID M5110, 3.46> disk fixed
sd1: fabricating a geometry
sd1: 271 GB, 278472 cyl, 64 head, 32 sec, 512 bytes/sect x 570310656 sectors
sd1: fabricating a geometry
sd1: tagged queueing
cdce0 at uhub4 port 5 configuration 1 interface 0
cdce0: IBM (0x04b3) RNDIS/Ethernet Gadget (0x4010), rev 2.00/3.25, addr 4
cdce0: Ethernet address 42:f2:e9:f1:b7:01
cdce0: detached
cdce0: at uhub4 port 5 (addr 4) disconnected
cdce0 at uhub4 port 5 configuration 1 interface 0
cdce0: IBM (0x04b3) RNDIS/Ethernet Gadget (0x4010), rev 2.00/3.25, addr 4
cdce0: Ethernet address 42:f2:e9:f1:b7:01
WARNING: 3 errors while detecting hardware; check system log.
boot device: dk0
root on dk0 dumps on dk1
Your machine does not initialize mem_clusters; sparse_dumps disabled
root file system type: ffs
kern.module.path=/stand/amd64/11.0/modules
ZFS filesystem version: 5
wsdisplay0: screen 1 added (80x25, vt100 emulation)
wsdisplay0: screen 2 added (80x25, vt100 emulation)
wsdisplay0: screen 3 added (80x25, vt100 emulation)
wsdisplay0: screen 4 added (80x25, vt100 emulation)
balloon0 at xenbus0 id 0: Xen Balloon driver
balloon0: current reservation: 1048576 KiB
ipmi0: version 2.0 interface KCS iobase 0xcc0/0x2 spacing 1
ipmi0: ID 32.0 IPMI 2.0 Available
ipmi0: Additional Chassis IPMBGen IPMBRcv FRU SEL SDR Sensor
ipmi0: Manufacturer 04f4d Product 014d
ipmi0: Firmware 8.41
>How-To-Repeat:
Get a working install with GENERIC on a server with a high number of CPUs (in this case, 24 including hyperthreading). Attempt to boot a DOM0 kernel.
>Fix:
A workaround is to set dom0_max_vcpus=1 on the xen command line. i.e. have the multiboot section of boot.cfg as:

multiboot /xen.gz dom0_mem=1024M dom0_max_vcpus=1 dom0_vcpus_pin