Add preflight check for hardware-assisted virtualization

This is pretty quick and dirty, but I hope should not be unreasonable.
https://help.ubuntu.com/community/KVM/Installation tells us that we need
to run `egrep -c '(vmx|svm)' /proc/cpuinfo` to check for hardware-assisted
virtualization on x86_64 systems, but I think we can short-circuit that.

I reviewed the kvm-ok script (https://bazaar.launchpad.net/~cpu-checker-dev/cpu-checker/trunk/view/head:/kvm-ok)
and it first checks for those CPU flags, and then next checks for the
existence of /dev/kvm.  If both succeed, we're good.  But I don't think
we actually need the CPU flag check, at least on SUSE distros.  I did some
testing, and AFAICT if the CPU supports hardware virtualization, the
appropriate kvm kernel module (e.g. kvm_intel) is loaded automatically,
so /dev/kvm will exist.  If not, the module doesn't get loaded and
/dev/kvm doesn't exist.

More recent changes to kvm-ok in Debian-based distros (see
https://sources.debian.org/patches/cpu-checker/0.7-1.3/) add support
for other architectures (aarch64, ppc*, s390x, riscv64), but in all those
cases, the only thing that happens is a check for the existence of /dev/kvm.

Signed-off-by: Tim Serong <[email protected]>

pkg/console/console.go

@@ -158,6 +158,7 @@ func (c *Console) doRun() error {
 			preflight.CPUCheck{},
 			preflight.MemoryCheck{},
 			preflight.VirtCheck{},
+			preflight.KVMHostCheck{},
 		}
 		for _, c := range checks {
 			msg, err := c.Run()

pkg/preflight/checks.go

@@ -4,6 +4,7 @@ import (
 	"bufio"
 	"errors"
 	"fmt"
+	"io/fs"
 	"os"
 	"os/exec"
 	"strconv"
@@ -23,6 +24,7 @@ var (
 	// So that we can fake this stuff up for unit tests
 	execCommand = exec.Command
 	procMemInfo = "/proc/meminfo"
+	devKvm      = "/dev/kvm"
 )
 
 // The Run() method of a preflight.Check returns a string.  If the string
@@ -36,6 +38,7 @@ type Check interface {
 type CPUCheck struct{}
 type MemoryCheck struct{}
 type VirtCheck struct{}
+type KVMHostCheck struct{}
 
 func (c CPUCheck) Run() (msg string, err error) {
 	out, err := execCommand("/usr/bin/nproc", "--all").Output()
@@ -118,3 +121,11 @@ func (c VirtCheck) Run() (msg string, err error) {
 	msg = fmt.Sprintf("System is virtualized (%s) which is not supported.", virt)
 	return
 }
+
+func (c KVMHostCheck) Run() (msg string, err error) {
+	if _, err = os.Stat(devKvm); errors.Is(err, fs.ErrNotExist) {
+		msg = "Harvester requires hardware-assisted virtualization, but /dev/kvm does not exist."
+		err = nil
+	}
+	return
+}

pkg/preflight/checks_test.go

@@ -129,3 +129,21 @@ func TestMemoryCheck(t *testing.T) {
 		assert.Equal(t, expectedOutput, msg)
 	}
 }
+
+func TestKVMHostCheck(t *testing.T) {
+	defaultDevKvm := devKvm
+	defer func() { devKvm = defaultDevKvm }()
+
+	expectedOutputs := map[string]string{
+		"./testdata/dev-kvm-does-not-exist": "Harvester requires hardware-assisted virtualization, but /dev/kvm does not exist.",
+		"./testdata/dev-kvm":                "",
+	}
+
+	check := KVMHostCheck{}
+	for file, expectedOutput := range expectedOutputs {
+		devKvm = file
+		msg, err := check.Run()
+		assert.Nil(t, err)
+		assert.Equal(t, expectedOutput, msg)
+	}
+}