Any comments on this? I'm not sure if the below patch is sufficient, or models such as qemu64 need to include vendor information. Thanks! Regards, Jim On 08/05/2016 03:38 PM, Jim Fehlig wrote:

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@suse.com> 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@suse.com> --- 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