feat: add swiotlb=noforce to default kernel command line

swiotlb=noforce disables SWIOTLB, which is enabled by the kernel if the
physical addresses exceed 32b. This is not needed for us and causes 64MB
to be wasted on the microvm.

Signed-off-by: Riccardo Mancini <mancio@amazon.com>

Author: Manciukic

src/vmm/src/vmm_config/boot_source.rs

@@ -14,8 +14,9 @@ use serde::{Deserialize, Serialize};
 /// - `i8042.noaux` do not probe the i8042 controller for an attached mouse (save boot time);
 /// - `i8042.nomux` do not probe i8042 for a multiplexing controller (save boot time);
 /// - `i8042.dumbkbd` do not attempt to control kbd state via the i8042 (save boot time).
-pub const DEFAULT_KERNEL_CMDLINE: &str =
-    "reboot=k panic=1 nomodule 8250.nr_uarts=0 i8042.noaux i8042.nomux i8042.dumbkbd";
+/// - `swiotlb=noforce` disable software bounce buffers (SWIOTLB)
+pub const DEFAULT_KERNEL_CMDLINE: &str = "reboot=k panic=1 nomodule 8250.nr_uarts=0 i8042.noaux \
+                                          i8042.nomux i8042.dumbkbd swiotlb=noforce";
 
 /// Strongly typed data structure used to configure the boot source of the
 /// microvm.

tests/framework/microvm.py

@@ -807,7 +807,7 @@ def basic_config(
 
         If boot_args is None, the default boot_args in Firecracker is
             reboot=k panic=1 nomodule 8250.nr_uarts=0 i8042.noaux i8042.nomux
-            i8042.nopnp i8042.dumbkbd
+            i8042.nopnp i8042.dumbkbd swiotlb=noforce
 
         if PCI is disabled, Firecracker also passes to the guest pci=off
 

tests/framework/microvm_helpers.py

@@ -127,7 +127,7 @@ def enable_console(self):
             raise RuntimeError(".spawn already called, too late to enable the console")
         if self.vm.boot_args is None:
             self.vm.boot_args = ""
-        self.vm.boot_args += "console=ttyS0 reboot=k panic=1"
+        self.vm.boot_args += "console=ttyS0 reboot=k panic=1 swiotlb=noforce"
         self.vm.jailer.daemonize = False
         self.vm.jailer.new_pid_ns = False
 

tests/framework/vm_config_missing_vcpu_count.json

@@ -1,7 +1,7 @@
 {
   "boot-source": {
     "kernel_image_path": "vmlinux.bin",
-    "boot_args": "console=ttyS0 reboot=k panic=1"
+    "boot_args": "console=ttyS0 reboot=k panic=1 swiotlb=noforce"
   },
   "drives": [
     {

tests/integration_tests/functional/test_error_code.py

@@ -25,7 +25,7 @@ def test_enosys_error_code(uvm_plain):
     vm.memory_monitor = None
     vm.basic_config(
         vcpu_count=1,
-        boot_args="reboot=k panic=1 init=/usr/local/bin/devmemread",
+        boot_args="reboot=k panic=1 swiotlb=noforce init=/usr/local/bin/devmemread",
     )
     vm.start()
 

tests/integration_tests/functional/test_kernel_cmdline.py

@@ -21,7 +21,7 @@ def test_init_params(uvm_plain):
     # Ubuntu version from the /etc/issue file.
     vm.basic_config(
         vcpu_count=1,
-        boot_args="console=ttyS0 reboot=k panic=1 init=/bin/cat -- /etc/issue",
+        boot_args="console=ttyS0 reboot=k panic=1 swiotlb=noforce init=/bin/cat -- /etc/issue",
     )
 
     vm.start()

tests/integration_tests/functional/test_serial_io.py

@@ -55,7 +55,7 @@ def test_serial_after_snapshot(uvm_plain, microvm_factory):
     microvm.basic_config(
         vcpu_count=2,
         mem_size_mib=256,
-        boot_args="console=ttyS0 reboot=k panic=1",
+        boot_args="console=ttyS0 reboot=k panic=1 swiotlb=noforce",
     )
     serial = Serial(microvm)
     serial.open()
@@ -99,7 +99,9 @@ def test_serial_console_login(uvm_plain_any):
     microvm.memory_monitor = None
 
     # Set up the microVM with 1 vCPU and a serial console.
-    microvm.basic_config(vcpu_count=1, boot_args="console=ttyS0 reboot=k panic=1")
+    microvm.basic_config(
+        vcpu_count=1, boot_args="console=ttyS0 reboot=k panic=1 swiotlb=noforce"
+    )
 
     microvm.start()
 
@@ -144,7 +146,7 @@ def test_serial_dos(uvm_plain_any):
     # Set up the microVM with 1 vCPU and a serial console.
     microvm.basic_config(
         vcpu_count=1,
-        boot_args="console=ttyS0 reboot=k panic=1",
+        boot_args="console=ttyS0 reboot=k panic=1 swiotlb=noforce",
     )
     microvm.add_net_iface()
     microvm.start()
@@ -178,7 +180,7 @@ def test_serial_block(uvm_plain_any):
     test_microvm.basic_config(
         vcpu_count=1,
         mem_size_mib=512,
-        boot_args="console=ttyS0 reboot=k panic=1",
+        boot_args="console=ttyS0 reboot=k panic=1 swiotlb=noforce",
     )
     test_microvm.add_net_iface()
     test_microvm.start()

tests/integration_tests/performance/test_boottime.py

@@ -12,7 +12,7 @@
 
 DEFAULT_BOOT_ARGS = (
     "reboot=k panic=1 nomodule 8250.nr_uarts=0"
-    " i8042.noaux i8042.nomux i8042.nopnp i8042.dumbkbd"
+    " i8042.noaux i8042.nomux i8042.nopnp i8042.dumbkbd swiotlb=noforce"
 )
 
 

tests/integration_tests/performance/test_initrd.py

@@ -35,7 +35,7 @@ def test_microvm_initrd_with_serial(uvm_with_initrd, huge_pages):
     vm.basic_config(
         add_root_device=False,
         vcpu_count=1,
-        boot_args="console=ttyS0 reboot=k panic=1",
+        boot_args="console=ttyS0 reboot=k panic=1 swiotlb=noforce",
         use_initrd=True,
         huge_pages=huge_pages,
     )