# Disco verification:

ubuntu@disco:~$ sudo /usr/bin/qemu-system-x86_64 -name guest="guest" -machine accel=kvm -cpu host,+arch-capabilities,+ssbd,+md-clear,+rdctl-no,+ibrs-all,+skip-l1dfl-vmentry,+mds-no -m 2048 -realtime mlock=off -smp 1,sockets=1,cores=1,threads=1 -uuid 7e55c71a-558f-412c-8445-db0e95fc549f -display none -no-user-config -nodefaults -rtc base=utc,driftfix=slew -global kvm-pit.lost_tick_policy=delay -no-shutdown -global PIIX4_PM.disable_s3=1 -global PIIX4_PM.disable_s4=1 -boot strict=on -kernel /var/lib/libvirt/images/guest/vmlinuz -initrd /var/lib/libvirt/images/guest/initrd.img -append "root=/dev/vda noresume console=tty0 console=ttyS0,38400n8 apparmor=0 net.ifnames=0 crashkernel=256M" -device piix3-usb-uhci,id=usb,bus=pci.0,addr=0x1.0x2 -drive file=/var/lib/libvirt/images/guest/disk01.ext4.qcow2,format=qcow2,if=none,id=drive-virtio-disk0 -device virtio-blk-pci,scsi=off,bus=pci.0,addr=0x3,drive=drive-virtio-disk0,id=virtio-disk0,bootindex=1 -device virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x4 -msg timestamp=on -serial stdio 

-> changing "host" to CascadeLake-Server also works the same way.

Provided me:

inaddy@guest:~$ cat /proc/cpuinfo
processor       : 0
vendor_id       : GenuineIntel
cpu family      : 6
model           : 85
model name      : Intel(R) Xeon(R) Gold 6252 CPU @ 2.10GHz
stepping        : 6
microcode       : 0x1
cpu MHz         : 2095.076
cache size      : 16384 KB
physical id     : 0
siblings        : 1
core id         : 0
cpu cores       : 1
apicid          : 0
initial apicid  : 0
fpu             : yes
fpu_exception   : yes
cpuid level     : 13
wp              : yes
flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 ss syscall nx pdpe1gb rdtscp lm constant_tsc arch_perfmon rep_good nopl xtopology cpuid tsc_known_freq pni pclmulqdq vmx ssse3 fma cx16 pcid sse4_1 sse4_2 x2apic movbe popcnt tsc_deadline_timer aes xsave avx f16c rdrand hypervisor lahf_lm abm 3dnowprefetch cpuid_fault invpcid_single ssbd ibrs ibpb ibrs_enhanced tpr_shadow vnmi flexpriority ept vpid fsgsbase tsc_adjust bmi1 hle avx2 smep bmi2 erms invpcid rtm mpx avx512f avx512dq rdseed adx smap clflushopt clwb avx512cd avx512bw avx512vl xsaveopt xsavec xgetbv1 xsaves arat umip pku ospke avx512_vnni md_clear arch_capabilities
bugs            : spectre_v1 spectre_v2 spec_store_bypass
bogomips        : 4190.15
clflush size    : 64
cache_alignment : 64
address sizes   : 40 bits physical, 48 bits virtual
power management:

AND reading the MSR directly:

inaddy@guest:~$ sudo rdmsr 0x10a
2b

We have bits: 0 1 3 and 5 like it should be.

-------------------------

Running same QEMU cmd line, enabling +arch-capabilities in CascadeLake-Server but without specifying any other CPU flags:

flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 syscall nx pdpe1gb rdtscp lm constant_tsc rep_good nopl xtopology cpuid tsc_known_freq pni pclmulqdq ssse3 fma cx16 pcid sse4_1 sse4_2 x2apic movbe popcnt tsc_deadline_timer aes xsave avx f16c rdrand hypervisor lahf_lm abm 3dnowprefetch cpuid_fault invpcid_single pti ssbd ibrs ibpb fsgsbase bmi1 hle avx2 smep bmi2 erms invpcid rtm mpx avx512f avx512dq rdseed adx smap clflushopt clwb avx512cd avx512bw avx512vl xsaveopt xsavec xgetbv1 arat pku ospke avx512_vnni arch_capabilities
bugs            : cpu_meltdown spectre_v1 spectre_v2 spec_store_bypass l1tf mds

inaddy@guest:~$ sudo rdmsr 0x10a
0

We are not enabling any mitigation flag in arch-capabilities MSR by default, like we planned so. All CPU capabilities are going to be enabled by hand and/or through libvirt XML definitions as soon as libvirt gets the capabilities (this same bug).

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Marking Disco as verified. 

Thank you!