[kvm-unit-tests PATCH v3 10/16] scripts: Add default arguments for kvmtool

Alexandru Elisei
2025-05-07T15:13:49Z

kvmtool, unless told otherwise, will do its best to make sure that a kernel
successfully boots in a virtual machine. It does things like automatically
creating a rootfs and adding extra parameters to the kernel command line.
This is actively harmful to kvm-unit-tests, because some tests parse the
kernel command line and they will fail if they encounter the options added
by kvmtool.

Fortunately for us, kvmtool commit 5613ae26b998 ("Add --nodefaults command
line argument") addded the --nodefaults kvmtool parameter which disables
all the implicit virtual machine configuration that cannot be disabled by
using other parameters, like modifying the kernel command line. So always
use --nodefaults to allow a test to run.

kvmtool can also be too verbose when running a virtual machine, and this is
controlled by several parameters. Add those to the default kvmtool command
line to reduce this verbosity to a minimum.

Before:

$ vm run arm/selftest.flat --cpus 2 --mem 256 --params "setup smp=2 mem=256"
Info: # lkvm run -k arm/selftest.flat -m 256 -c 2 --name guest-5035
Unknown subtest

EXIT: STATUS=127
Warning: KVM compatibility warning.
virtio-9p device was not detected.
While you have requested a virtio-9p device, the guest kernel did not initialize it.
Please make sure that the guest kernel was compiled with CONFIG_NET_9P_VIRTIO=y enabled in .config.
Warning: KVM compatibility warning.
virtio-net device was not detected.
While you have requested a virtio-net device, the guest kernel did not initialize it.
Please make sure that the guest kernel was compiled with CONFIG_VIRTIO_NET=y enabled in .config.
Info: KVM session ended normally.

After:

$ vm run arm/selftest.flat --nodefaults --network mode=none --loglevel=warning --cpus 2 --mem 256 --params "setup smp=2 mem=256"
PASS: selftest: setup: smp: number of CPUs matches expectation
INFO: selftest: setup: smp: found 2 CPUs
PASS: selftest: setup: mem: memory size matches expectation
INFO: selftest: setup: mem: found 256 MB
SUMMARY: 2 tests

EXIT: STATUS=1

Note that KVMTOOL_DEFAULT_OPTS can be overwritten by an environment
variable with the same name, but it's not documented in the help string for
run_tests.sh. This has been done on purpose, since overwritting
KVMTOOL_DEFAULT_OPTS should only be necessary for debugging or development
purposes.

Signed-off-by: Alexandru Elisei <alexandru.elisei@arm.com>
---
scripts/common.bash | 10 +++++-----
scripts/vmm.bash | 13 +++++++++++++
2 files changed, 18 insertions(+), 5 deletions(-)

diff --git a/scripts/common.bash b/scripts/common.bash
index 0645235d8baa..ee0ae71948c2 100644
--- a/scripts/common.bash
+++ b/scripts/common.bash
@@ -56,7 +56,7 @@ function for_each_unittest()
# because qemu interprets the first argument after
# -append as a kernel parameter.
test_args=""
- opts=""
+ opts="${vmm_opts[$TARGET:default_opts]}"
groups=""
arch=""
machine=""
@@ -70,13 +70,13 @@ function for_each_unittest()
elif [[ $line =~ ^test_args\ *=\ *(.*)$ ]]; then
test_args="${vmm_opts[$TARGET:args]} ${BASH_REMATCH[1]}"
elif [[ $TARGET = "qemu" ]] && [[ $line =~ ^(extra_params|qemu_params)\ *=\ *'"""'(.*)$ ]]; then
- opts=$(parse_opts ${BASH_REMATCH[2]}$'\n' $fd)
+ opts="${vmm_opts[$TARGET:default_opts]} $(parse_opts ${BASH_REMATCH[2]}$'\n' $fd)"
elif [[ $TARGET = "qemu" ]] && [[ $line =~ ^(extra_params|qemu_params)\ *=\ *(.*)$ ]]; then
- opts=${BASH_REMATCH[2]}
+ opts="${vmm_opts[$TARGET:default_opts]} ${BASH_REMATCH[2]}"
elif [[ $TARGET = "kvmtool" ]] && [[ $line =~ ^kvmtool_params\ *=\ *'"""'(.*)$ ]]; then
- opts=$(parse_opts ${BASH_REMATCH[1]}$'\n' $fd)
+ opts="${vmm_opts[$TARGET:default_opts]} $(parse_opts ${BASH_REMATCH[1]}$'\n' $fd)"
elif [[ $TARGET = "kvmtool" ]] && [[ $line =~ ^kvmtool_params\ *=\ *(.*)$ ]]; then
- opts=${BASH_REMATCH[1]}
+ opts="${vmm_opts[$TARGET:default_opts]} ${BASH_REMATCH[1]}"
elif [[ $line =~ ^groups\ *=\ *(.*)$ ]]; then
groups=${BASH_REMATCH[1]}
elif [[ $line =~ ^arch\ *=\ *(.*)$ ]]; then
diff --git a/scripts/vmm.bash b/scripts/vmm.bash
index 20968f2e6b10..d24a4c4b8713 100644
--- a/scripts/vmm.bash
+++ b/scripts/vmm.bash
@@ -1,5 +1,16 @@
source config.mak

+# The following parameters are enabled by default when running a test with
+# kvmtool:
+# --nodefaults: suppress VM configuration that cannot be disabled otherwise
+# (like modifying the supplied kernel command line). Tests that
+# use the command line will fail without this parameter.
+# --network mode=none: do not create a network device. kvmtool tries to help the
+# user by automatically create one, and then prints a warning
+# when the VM terminates if the device hasn't been initialized.
+# --loglevel=warning: reduce verbosity
+: "${KVMTOOL_DEFAULT_OPTS:="--nodefaults --network mode=none --loglevel=warning"}"
+
##############################################################################
# qemu_fixup_return_code translates the ambiguous exit status in Table1 to that
# in Table2. Table3 simply documents the complete status table.
@@ -87,12 +98,14 @@ declare -A vmm_opts=(
[qemu:kernel]='-kernel'
[qemu:args]='-append'
[qemu:initrd]='-initrd'
+ [qemu:default_opts]=''
[qemu:fixup_return_code]=qemu_fixup_return_code

[kvmtool:nr_cpus]='--cpus'
[kvmtool:kernel]='--kernel'
[kvmtool:args]='--params'
[kvmtool:initrd]='--initrd'
+ [kvmtool:default_opts]="$KVMTOOL_DEFAULT_OPTS"
[kvmtool:fixup_return_code]=kvmtool_fixup_return_code
)

--
2.49.0