I have an L1 nested VM with the following cpu
# lscpu
Architecture: x86_64
CPU op-mode(s): 32-bit, 64-bit
Byte Order: Little Endian
CPU(s): 2
On-line CPU(s) list: 0,1
Thread(s) per core: 1
Core(s) per socket: 1
Socket(s): 2
NUMA node(s): 1
Vendor ID: AuthenticAMD
CPU family: 6
Model: 2
Model name: QEMU Virtual CPU version 0.14
Stepping: 3
CPU MHz: 3092.210
BogoMIPS: 6184.42
Virtualization: AMD-V
Hypervisor vendor: KVM
Virtualization type: full
L1d cache: 64K
L1i cache: 64K
L2 cache: 512K
NUMA node0 CPU(s): 0,1
Flags: fpu de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov
pat pse36 clflush mmx fxsr sse sse2 syscall nx lm nopl pni cx16 popcnt
hypervisor lahf_lm svm abm sse4a 3dnowprefetch vmmcall
When starting an L2 VM with <cpu mode="host-model">, libvirtd in the L1 VM crashes
Program received signal SIGSEGV, Segmentation fault.
0x00007ffff739bf33 in x86DataCpuid (cpuid=0x8, cpuid=0x8,
data=data@entry=0x7fffb800ee78) at cpu/cpu_x86.c:287
287 for (i = 0; i < data->len; i++) {
(gdb) bt
f0 0x00007ffff739bf33 in x86DataCpuid (cpuid=0x8, cpuid=0x8,
data=data@entry=0x7fffb800ee78) at cpu/cpu_x86.c:287
f1 virCPUx86DataAddCPUID (data=data@entry=0x7fffb800ee78, cpuid=0x8)
at cpu/cpu_x86.c:355
f2 0x00007ffff739ef47 in x86Compute (host=<optimized out>, cpu=0x7fffb8000cc0,
guest=0x7fffecca7348, message=<optimized out>) at cpu/cpu_x86.c:1580
f3 0x00007fffd2b38e53 in qemuBuildCpuModelArgStr (migrating=false,
hasHwVirt=<synthetic pointer>, qemuCaps=0x7fffb8001040, buf=0x7fffecca7360,
def=0x7fffc400ce20, driver=0x1c) at qemu/qemu_command.c:6283
f4 qemuBuildCpuCommandLine (cmd=cmd@entry=0x7fffb8002f60,
driver=driver@entry=0x7fffc80882c0, def=def@entry=0x7fffc400ce20,
qemuCaps=qemuCaps@entry=0x7fffb8001040, migrating=<optimized out>)
at qemu/qemu_command.c:6445
In frame 2, &host_model->vendor->cpuid is passed to virCPUx86DataAddCPUID(),
but
(gdb) p *host_model
$23 = {name = 0x7fffb800ec50 "qemu64", vendor = 0x0, signature = 0, data = {
len = 2, data = 0x7fffb800e720}}
With vendor = 0x0, &host_model->vendor->cpuid evaluates to 8, which is not a
nice value to pass to virCPUx86DataAddCPUID(). I've hacked around the problem by
checking for a non-null host->vendor before calling
virCPUx86DataAddCPUID, but I get the feeling it is just that - a hack.
Comments on the attached patch, or suggestions for an alternate fix, are kindly
welcomed :-).
Regards,
Jim
>From 341445ce85d91a105f8183f22226d9d90853b27b Mon Sep 17 00:00:00 2001
From: Jim Fehlig <jfehlig@xxxxxxxx>
Date: Fri, 5 Aug 2016 15:23:47 -0600
Subject: [PATCH] cpu_x86: fix libvirtd crash when host cpu is 'qemu64'
When starting an L2 nested VM with <cpu mode="host-model"> on an
L1 VM with cpu 'qemu64', libvirtd crashes with
Program received signal SIGSEGV, Segmentation fault.
0x00007ffff739bf33 in x86DataCpuid (cpuid=0x8, cpuid=0x8,
data=data@entry=0x7fffb800ee78) at cpu/cpu_x86.c:287
287 for (i = 0; i < data->len; i++) {
(gdb) bt
f0 0x00007ffff739bf33 in x86DataCpuid (cpuid=0x8, cpuid=0x8,
data=data@entry=0x7fffb800ee78) at cpu/cpu_x86.c:287
f1 virCPUx86DataAddCPUID (data=data@entry=0x7fffb800ee78, cpuid=0x8)
at cpu/cpu_x86.c:355
f2 0x00007ffff739ef47 in x86Compute (host=<optimized out>, cpu=0x7fffb8000cc0,
guest=0x7fffecca7348, message=<optimized out>) at cpu/cpu_x86.c:1580
f3 0x00007fffd2b38e53 in qemuBuildCpuModelArgStr (migrating=false,
hasHwVirt=<synthetic pointer>, qemuCaps=0x7fffb8001040, buf=0x7fffecca7360,
def=0x7fffc400ce20, driver=0x1c) at qemu/qemu_command.c:6283
f4 qemuBuildCpuCommandLine (cmd=cmd@entry=0x7fffb8002f60,
driver=driver@entry=0x7fffc80882c0, def=def@entry=0x7fffc400ce20,
qemuCaps=qemuCaps@entry=0x7fffb8001040, migrating=<optimized out>)
at qemu/qemu_command.c:6445
In frame 2, &host_model->vendor->cpuid is passed to virCPUx86DataAddCPUID(),
but
(gdb) p *host_model
$23 = {name = 0x7fffb800ec50 "qemu64", vendor = 0x0, signature = 0, data = {
len = 2, data = 0x7fffb800e720}}
With vendor = 0x0, &host_model->vendor->cpuid evaluates to 8, which
is not a nice value to pass to virCPUx86DataAddCPUID(). Check for a
non-null host_model->vendor before calling virCPUx86DataAddCPUID().
Signed-off-by: Jim Fehlig <jfehlig@xxxxxxxx>
---
src/cpu/cpu_x86.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/src/cpu/cpu_x86.c b/src/cpu/cpu_x86.c
index d9646eb..09eaaa2 100644
--- a/src/cpu/cpu_x86.c
+++ b/src/cpu/cpu_x86.c
@@ -1576,7 +1576,7 @@ x86Compute(virCPUDefPtr host,
if (!(guest_model = x86ModelCopy(host_model)))
goto error;
- if (cpu->vendor &&
+ if (cpu->vendor && host_model->vendor &&
virCPUx86DataAddCPUID(&guest_model->data,
&host_model->vendor->cpuid) < 0)
goto error;
--
2.1.4
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