qemu: moving toward nesting VMs

3 files changed, 35 insertions, 1 deletions

diff --git a/Makefile b/Makefile
index ce5803e..4f75fe9 100644
--- a/Makefile
+++ b/Makefile
@@ -36,6 +36,10 @@ samizdat-paths.sh: src/samizdat-paths.in
         @sed -e "s?PREFIX?$(prefix)?g" $< > $@
 include samizdat-paths.sh
 
+install-nested-kvm: conf/kvm.conf
+        install -m0644 conf/kvm.conf ${instdir}/etc/modprobe.d/
+        modprobe -r kvm-intel kvm-amd kvm; modprobe kvm; modprobe kvm-intel; modprobe kvm-amd; true
+
 install-configuration:
 ifndef instdir
         $(error "You must specify instdir, for safety.")
diff --git a/conf/kvm.conf b/conf/kvm.conf
new file mode 100644
index 0000000..dfc2d9d
--- /dev/null
+++ b/conf/kvm.conf
@@ -0,0 +1,2 @@
+options kvm_intel nested=1
+options kvm_amd nested=1
diff --git a/src/qemu.sh b/src/qemu.sh
index 8f365cb..2ae982d 100755
--- a/src/qemu.sh
+++ b/src/qemu.sh
@@ -64,8 +64,36 @@ if [ ! -e "$disk" ]; then
     fallocate -l 10GB "$disk"
 fi
 
+if grep -q '^flags.*\<vmx\>' /proc/cpuinfo; then
+    kvm='-enable-kvm -cpu host'
+    read nested < /sys/module/kvm_intel/parameters/nested
+    if [ "$nested" != Y ]; then
+        printf '%s\n' \
+               'Warning: nested KVM is not available' \
+               'Try "make install-nested-kvm"'
+    fi
+else
+    >&2 printf '%s\n' \
+        '' \
+        'Warning: kernel virtual machine extensions (KVM) not available.' \
+        'The VM will be intolerably slow.' \
+        'If your hardware supports KVM, you need to enable it in the BIOS.' \
+        '' \
+        'If you are trying to run qemu in a virtual machine, you need to append' \
+        'the kvm-(intel|amd) module parameter "nested=1" on the _host_ machine.' \
+        'Use "make install-nested-kvm" to do so.' \
+        ''
+    kvm=
+fi
+
+mem_total=$(grep MemTotal /proc/meminfo | (read _ kb _; echo $((kb / 1024))))
+use_mem=640
+if [ "$mem_total" -le $((use_mem * 2)) ]; then
+  use_mem=$((mem_total / 2))
+fi
+
 set -x
-sudo ${qemu} -enable-kvm -smp 2 -m 640 -k en-us \
+sudo ${qemu} ${kvm} -smp 2 -m ${use_mem} -k en-us \
      -vga qxl \
      -net nic,model=virtio,macaddr=$MAC \
      ${USE_NET:+ -net "$NET"} \