* [pve-devel] [PATCH qemu-server] cpu config: nested-virt: always recommend a CPU model similar to the host
@ 2025-11-19 9:59 Fiona Ebner
2025-11-19 11:23 ` Thomas Lamprecht
0 siblings, 1 reply; 2+ messages in thread
From: Fiona Ebner @ 2025-11-19 9:59 UTC (permalink / raw)
To: pve-devel
Not only for Windows, nested virtualization with just x86-64-v2-AES
and the nested-virt flag does not work on Linux either. While
virtualization support is detected, actually starting a nested VM with
such a configuration fails. For example, a Proxmox VE/PBS file-restore
VM on my test system fails with the following (adding the apic and
x2apic flags on top wouldn't make a difference):
[2025-11-19T10:37:44+01:00] PBS file restore VM log
ERROR: Unable to locate IOAPIC for GSI 2
ERROR: Unable to locate IOAPIC for GSI 5
ERROR: Unable to locate IOAPIC for GSI 9
ERROR: Unable to locate IOAPIC for GSI 10
ERROR: Unable to locate IOAPIC for GSI 11
ERROR: Unable to locate IOAPIC for GSI 1
ERROR: Unable to locate IOAPIC for GSI 2
ERROR: Unable to locate IOAPIC for GSI 3
ERROR: Unable to locate IOAPIC for GSI 4
ERROR: Unable to locate IOAPIC for GSI 5
ERROR: Unable to locate IOAPIC for GSI 6
ERROR: Unable to locate IOAPIC for GSI 7
ERROR: Unable to locate IOAPIC for GSI 8
ERROR: Unable to locate IOAPIC for GSI 9
ERROR: Unable to locate IOAPIC for GSI 10
ERROR: Unable to locate IOAPIC for GSI 11
ERROR: Unable to locate IOAPIC for GSI 12
ERROR: Unable to locate IOAPIC for GSI 13
ERROR: Unable to locate IOAPIC for GSI 14
ERROR: Unable to locate IOAPIC for GSI 15
..MP-BIOS bug: 8254 timer not connected to IO-APIC
Kernel panic - not syncing: IO-APIC + timer doesn't work! Boot with apic=debug and send a report. Then try booting with the 'noapic' option.
CPU: 0 UID: 0 PID: 0 Comm: swapper/0 Tainted: G W 6.14.6-pbs-restore #1
Tainted: [W]=WARN
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.17.0-0-gb52ca86e094d-prebuilt.qemu.org 04/01/2014
Call Trace:
<TASK>
dump_stack_lvl+0x4a/0x70
panic+0xf5/0x281
? _printk+0x55/0x60
setup_IO_APIC+0x6ee/0x6f0
? __ioapic_read_entry+0x23/0x40
? clear_IO_APIC_pin+0x11e/0x1e0
apic_intr_mode_init+0xad/0xc0
x86_late_time_init+0x12/0x30
start_kernel+0x538/0x5b0
x86_64_start_reservations+0x25/0x30
x86_64_start_kernel+0x73/0x80
common_startup_64+0x129/0x138
</TASK>
Reported-by: Lukas Wagner <l.wagner@proxmox.com>
Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
---
src/PVE/QemuServer/CPUConfig.pm | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/src/PVE/QemuServer/CPUConfig.pm b/src/PVE/QemuServer/CPUConfig.pm
index c0d4c9a4..b63743be 100644
--- a/src/PVE/QemuServer/CPUConfig.pm
+++ b/src/PVE/QemuServer/CPUConfig.pm
@@ -170,7 +170,7 @@ my $supported_cpu_flags = [
name => 'nested-virt',
description => "Controls nested virtualization, namely 'svm' for AMD CPUs and 'vmx' for"
. " Intel CPUs. Live migration still only works if it's the same flag on both sides."
- . " For Windows, use a CPU model similar to the host, with the same vendor!",
+ . " Use a CPU model similar to the host, with the same vendor, not x86-64-vX!",
},
{
name => 'md-clear',
--
2.47.3
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2025-11-19 9:59 [pve-devel] [PATCH qemu-server] cpu config: nested-virt: always recommend a CPU model similar to the host Fiona Ebner
2025-11-19 11:23 ` Thomas Lamprecht
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