qemu: arm64: Don't detect gic version by /proc/interrupts

Commit b438590 ("qemu/arm64: Detect host GIC version to configure guest
GIC") reads /proc/interrupts to detect the host gic version.

But on a ThunderX2 host with 224 cpus, the /proc/interrupts is ~762K bytes.
Hence it will costs ~900K bytes memory overhead.
From the go tool pprof results:
      flat  flat%   sum%        cum   cum%
  976.89kB   100%   100%   976.89kB   100%  github.com/kata-containers/runtime/virtcontainers.getHostGICVersion
Although the allocated memory will be freed, seems it worthy removing that
for speed up the runtime.

As per [1], there is no perfect way to detect the gic version on host.
At qemu side, if we use "gic-version=host", qemu will automatically detect
the verion by kvm ioctl. So we'd better let qemu determine the gic version.

If the user really want to start vm with gic-verion=2, he/she can set it
in machine_accelerators option.

[1]https://lists.cs.columbia.edu/pipermail/kvmarm/2014-October/011690.html

Fixes: #2614
Signed-off-by: Jia He <[email protected]>

virtcontainers/qemu_arm64.go

@@ -7,13 +7,10 @@ package virtcontainers
 
 import (
 	"context"
-	"io/ioutil"
 	"runtime"
-	"strings"
 	"time"
 
 	govmmQemu "github.com/intel/govmm/qemu"
-	"github.com/sirupsen/logrus"
 )
 
 type qemuArm64 struct {
@@ -27,7 +24,7 @@ const defaultQemuMachineType = QemuVirt
 
 const qmpMigrationWaitTimeout = 10 * time.Second
 
-var defaultQemuMachineOptions = "usb=off,accel=kvm,gic-version=" + getGuestGICVersion()
+const defaultQemuMachineOptions = "usb=off,accel=kvm,gic-version=host"
 
 var qemuPaths = map[string]string{
 	QemuVirt: defaultQemuPath,
@@ -46,65 +43,6 @@ var supportedQemuMachines = []govmmQemu.Machine{
 	},
 }
 
-// Logger returns a logrus logger appropriate for logging qemu-aarch64 messages
-func qemuArmLogger() *logrus.Entry {
-	return virtLog.WithField("subsystem", "qemu-aarch64")
-}
-
-// On ARM platform, we have different GIC interrupt controllers. Different
-// GIC supports different QEMU parameters for virtual GIC and max VCPUs
-var hostGICVersion = getHostGICVersion()
-
-// We will access this file on host to detect host GIC version
-var gicProfile = "/proc/interrupts"
-
-// Detect the host GIC version.
-// Success: return the number of GIC version
-// Failed: return 0
-func getHostGICVersion() (version uint32) {
-	bytes, err := ioutil.ReadFile(gicProfile)
-	if err != nil {
-		qemuArmLogger().WithField("GIC profile", gicProfile).WithError(err).Error("Failed to parse GIC profile")
-		return 0
-	}
-
-	s := string(bytes)
-	if strings.Contains(s, "GICv2") {
-		return 2
-	}
-
-	if strings.Contains(s, "GICv3") {
-		return 3
-	}
-
-	if strings.Contains(s, "GICv4") {
-		return 4
-	}
-
-	return 0
-}
-
-// QEMU supports GICv2, GICv3 and host parameters for gic-version. The host
-// parameter will let QEMU detect GIC version by itself. This parameter
-// will work properly when host GIC version is GICv2 or GICv3. But the
-// detection will failed when host GIC is gicv4 or higher. In this case,
-// we have to detect the host GIC version manually and force QEMU to use
-// GICv3 when host GIC is GICv4 or higher.
-func getGuestGICVersion() (version string) {
-	if hostGICVersion == 2 {
-		return "2"
-	}
-
-	if hostGICVersion >= 3 {
-		return "3"
-	}
-
-	// We can't parse valid host GIC version from GIC profile.
-	// But we can use "host" to ask QEMU to detect valid GIC
-	// through KVM API for a try.
-	return "host"
-}
-
 //In qemu, maximum number of vCPUs depends on the GIC version, or on how
 //many redistributors we can fit into the memory map.
 //related codes are under github.com/qemu/qemu/hw/arm/virt.c(Line 135 and 1306 in stable-2.11)
@@ -118,9 +56,6 @@ var gicList = map[uint32]uint32{
 
 // MaxQemuVCPUs returns the maximum number of vCPUs supported
 func MaxQemuVCPUs() uint32 {
-	if hostGICVersion != 0 {
-		return gicList[hostGICVersion]
-	}
 	return uint32(runtime.NumCPU())
 }