pmbootstrap qemu: add aarch64 big/little hack (MR 1983)

Workaround for qemu failing with:
  kvm_arm_vcpu_init failed: invalid argument.

Related: https://bugs.linaro.org/show_bug.cgi?id=1443

pmb/parse/__init__.py

@@ -7,4 +7,5 @@ from pmb.parse.binfmt_info import binfmt_info
 from pmb.parse.deviceinfo import deviceinfo
 from pmb.parse.kconfig import check
 from pmb.parse.bootimg import bootimg
+from pmb.parse.cpuinfo import arm_big_little_first_group_ncpus
 import pmb.parse.arch

pmb/parse/cpuinfo.py

@@ -0,0 +1,32 @@
+# Copyright 2020 Lary Gibaud
+# SPDX-License-Identifier: GPL-3.0-or-later
+import re
+
+
+def arm_big_little_first_group_ncpus():
+    """
+    Infer from /proc/cpuinfo on aarch64 if this is a big/little architecture
+    (if there is different processor models) and the number of cores in the
+    first model group.
+    https://en.wikipedia.org/wiki/ARM_big.LITTLE
+
+    :returns: the number of cores of the first model in the order given by
+              linux or None if not big/little architecture
+    """
+    pattern = re.compile(r"^CPU part\s*: (\w+)$")
+    counter = 0
+    part = None
+
+    with open('/proc/cpuinfo', 'r') as cpuinfo:
+        for line in cpuinfo:
+            match = pattern.match(line)
+            if match:
+                grp = match.group(1)
+                if not part:
+                    part = grp
+                    counter += 1
+                elif part == grp:
+                    counter += 1
+                else:
+                    return counter
+        return None

pmb/qemu/run.py

@@ -15,6 +15,7 @@ import pmb.chroot.initfs
 import pmb.config
 import pmb.helpers.run
 import pmb.parse.arch
+import pmb.parse.cpuinfo
 
 
 def system_image(args):
@@ -84,6 +85,7 @@ def command_qemu(args, arch, img_path):
     suffix = "rootfs_" + args.device
     rootfs = args.work + "/chroot_" + suffix
     flavor = pmb.chroot.other.kernel_flavors_installed(args, suffix)[0]
+    ncpus = os.cpu_count()
 
     if args.host_qemu:
         qemu_bin = which_qemu(args, arch)
@@ -102,8 +104,23 @@ def command_qemu(args, arch, img_path):
                         "XDG_DATA_DIRS": rootfs_native + "/usr/local/share:" +
                         rootfs_native + "/usr/share"})
 
-        command = [rootfs_native + "/lib/ld-musl-" +
-                   args.arch_native + ".so.1"]
+        command = []
+        if args.arch_native in ["aarch64", "armv7"]:
+            # Workaround for QEMU failing on aarch64 asymetric multiprocessor arch
+            # (big/little architecture https://en.wikipedia.org/wiki/ARM_big.LITTLE)
+            # see https://bugs.linaro.org/show_bug.cgi?id=1443
+            ncpus_bl = pmb.parse.cpuinfo.arm_big_little_first_group_ncpus()
+            if ncpus_bl:
+                ncpus = ncpus_bl
+                logging.info("QEMU will run on big/little architecture on the"
+                             f" first {ncpus} cores (from /proc/cpuinfo)")
+                command += [rootfs_native + "/lib/ld-musl-" +
+                            args.arch_native + ".so.1"]
+                command += [rootfs_native + "/usr/bin/taskset"]
+                command += ["-c", "0-" + str(ncpus - 1)]
+
+        command += [rootfs_native + "/lib/ld-musl-" +
+                    args.arch_native + ".so.1"]
         command += ["--library-path=" + rootfs_native + "/lib:" +
                     rootfs_native + "/usr/lib:" +
                     rootfs_native + "/usr/lib/pulseaudio"]
@@ -115,7 +132,8 @@ def command_qemu(args, arch, img_path):
     command += ["-initrd", rootfs + "/boot/initramfs-" + flavor]
     command += ["-append", shlex.quote(cmdline)]
 
-    command += ["-smp", str(os.cpu_count())]
+    command += ["-smp", str(ncpus)]
+
     command += ["-m", str(args.memory)]
 
     command += ["-serial", "stdio"]