https://lore.kernel.org/stable/20191111173757.gb11...@linux.intel.com/

Discussion about why this is causing an issue on LTS/stable kernels, but
not upstream.

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https://bugs.launchpad.net/bugs/1852047

Title:
  [Bionic][Regression] Disabling EPT results in KVM guests that won't
  start

Status in linux package in Ubuntu:
  Invalid
Status in linux source package in Bionic:
  New

Bug description:
  Starting with 4.15.0-68.77, currently in bionic-proposed, I can no
  longer launch VMs when I disable EPT support in the kvm_intel module.
  This works fine under 4.15.0-66.75 from bionic-security.

   ubuntu@vought:~$ cat /proc/version_signature
   Ubuntu 4.15.0-68.77-generic 4.15.18
   ubuntu@vought:~$ sudo rmmod kvm_intel
   ubuntu@vought:~$ sudo modprobe kvm_intel ept=0
   ubuntu@vought:~$ cat /sys/module/kvm_intel/parameters/ept
   N
   ubuntu@vought:~$ virsh start --console l1
   Domain l1 started
   Connected to domain l1
   Escape character is ^]

  Under 4.15.0-66.75, I see full console output from the guest and reach
  a login prompt. Under 4.15.0-68.77, I see no output and the VM is
  unresponsive. I see nothing of use in /var/log/libvirt/qemu/l1.log.

  I see this on the following system:

  ubuntu@vought:~$ lscpu
  Architecture:        x86_64
  CPU op-mode(s):      32-bit, 64-bit
  Byte Order:          Little Endian
  CPU(s):              96
  On-line CPU(s) list: 0-95
  Thread(s) per core:  2
  Core(s) per socket:  24
  Socket(s):           2
  NUMA node(s):        2
  Vendor ID:           GenuineIntel
  CPU family:          6
  Model:               85
  Model name:          Intel(R) Xeon(R) Gold 6252 CPU @ 2.10GHz
  Stepping:            6
  CPU MHz:             1000.135
  CPU max MHz:         3700.0000
  CPU min MHz:         1000.0000
  BogoMIPS:            4200.00
  Virtualization:      VT-x
  L1d cache:           32K
  L1i cache:           32K
  L2 cache:            1024K
  L3 cache:            36608K
  NUMA node0 CPU(s):   0-23,48-71
  NUMA node1 CPU(s):   24-47,72-95
  Flags:               fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca 
cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx 
pdpe1gb rdtscp lm constant_tsc art arch_perfmon pebs bts rep_good nopl 
xtopology nonstop_tsc cpuid aperfmperf pni pclmulqdq dtes64 monitor ds_cpl vmx 
smx est tm2 ssse3 sdbg fma cx16 xtpr pdcm pcid dca sse4_1 sse4_2 x2apic movbe 
popcnt tsc_deadline_timer aes xsave avx f16c rdrand lahf_lm abm 3dnowprefetch 
cpuid_fault epb cat_l3 cdp_l3 invpcid_single ssbd mba ibrs ibpb stibp 
ibrs_enhanced tpr_shadow vnmi flexpriority ept vpid fsgsbase tsc_adjust bmi1 
hle avx2 smep bmi2 erms invpcid rtm cqm mpx rdt_a avx512f avx512dq rdseed adx 
smap clflushopt clwb intel_pt avx512cd avx512bw avx512vl xsaveopt xsavec 
xgetbv1 xsaves cqm_llc cqm_occup_llc cqm_mbm_total cqm_mbm_local dtherm ida 
arat pln pts hwp hwp_act_window hwp_epp hwp_pkg_req pku ospke avx512_vnni 
md_clear flush_l1d arch_capabilities

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