allow combination of initrd and hugepages

After simply giving it a try, it seems that this combination of features
actually works. So remove all the error branches that disallow it, and
update the negative test into a positive test.

Signed-off-by: Patrick Roy <[email protected]>

Author: roypat

docs/hugepages.md

@@ -39,7 +39,6 @@ Currently, hugetlbfs support is mutually exclusive with the following
 Firecracker features:
 
 - Memory Ballooning via the [Balloon Device](./ballooning.md)
-- Initrd
 
 ## FAQ
 

src/vmm/src/resources.rs

@@ -264,13 +264,6 @@ impl VmResources {
         if self.balloon.get().is_some() && updated.huge_pages != HugePageConfig::None {
             return Err(MachineConfigError::BalloonAndHugePages);
         }
-
-        if self.boot_source.config.initrd_path.is_some()
-            && updated.huge_pages != HugePageConfig::None
-        {
-            return Err(MachineConfigError::InitrdAndHugePages);
-        }
-
         self.machine_config = updated;
 
         Ok(())
@@ -337,12 +330,6 @@ impl VmResources {
         &mut self,
         boot_source_cfg: BootSourceConfig,
     ) -> Result<(), BootSourceConfigError> {
-        if boot_source_cfg.initrd_path.is_some()
-            && self.machine_config.huge_pages != HugePageConfig::None
-        {
-            return Err(BootSourceConfigError::HugePagesAndInitRd);
-        }
-
         self.boot_source = BootSource {
             builder: Some(BootConfig::new(&boot_source_cfg)?),
             config: boot_source_cfg,

src/vmm/src/vmm_config/boot_source.rs

@@ -42,8 +42,6 @@ pub enum BootSourceConfigError {
     InvalidInitrdPath(io::Error),
     /// The kernel command line is invalid: {0}
     InvalidKernelCommandLine(String),
-    /// Firecracker's huge pages support is incompatible with initrds.
-    HugePagesAndInitRd,
 }
 
 /// Holds the kernel specification (both configuration as well as runtime details).

src/vmm/src/vmm_config/machine_config.rs

@@ -31,8 +31,6 @@ pub enum MachineConfigError {
     KernelVersion,
     /// Firecracker's huge pages support is incompatible with memory ballooning.
     BalloonAndHugePages,
-    /// Firecracker's huge pages support is incompatible with initrds.
-    InitrdAndHugePages,
 }
 
 /// Describes the possible (huge)page configurations for a microVM's memory.

tests/integration_tests/performance/test_huge_pages.py

@@ -7,9 +7,10 @@
 import pytest
 
 from framework import utils
-from framework.microvm import HugePagesConfig
+from framework.microvm import HugePagesConfig, Serial
 from framework.properties import global_props
 from framework.utils_ftrace import ftrace_events
+from integration_tests.functional.test_initrd import INITRD_FILESYSTEM
 from integration_tests.functional.test_uffd import SOCKET_PATH, spawn_pf_handler
 
 
@@ -259,33 +260,19 @@ def test_negative_huge_pages_plus_initrd(uvm_with_initrd):
     uvm_with_initrd.spawn()
     uvm_with_initrd.memory_monitor = None
 
-    # Ensure setting huge pages and then telling FC to boot an initrd does not work
-    with pytest.raises(
-        RuntimeError,
-        match="Boot source error: Firecracker's huge pages support is incompatible with initrds.",
-    ):
-        # `basic_config` first does a PUT to /machine-config, which will apply the huge pages configuration,
-        # and then a PUT to /boot-source, which will register the initrd
-        uvm_with_initrd.basic_config(
-            boot_args="console=ttyS0 reboot=k panic=1 pci=off",
-            use_initrd=True,
-            huge_pages=HugePagesConfig.HUGETLBFS_2MB,
-            add_root_device=False,
-            vcpu_count=1,
-        )
-
-    # Ensure telling FC about the initrd first and then setting huge pages doesn't work
-    # This first does a PUT to /machine-config to reset the huge pages configuration, before doing a
-    # PUT to /boot-source to register the initrd
+    # `basic_config` first does a PUT to /machine-config, which will apply the huge pages configuration,
+    # and then a PUT to /boot-source, which will register the initrd
     uvm_with_initrd.basic_config(
-        huge_pages=HugePagesConfig.NONE,
         boot_args="console=ttyS0 reboot=k panic=1 pci=off",
         use_initrd=True,
+        huge_pages=HugePagesConfig.HUGETLBFS_2MB,
+        add_root_device=False,
+        vcpu_count=1,
     )
-    with pytest.raises(
-        RuntimeError,
-        match="Machine config error: Firecracker's huge pages support is incompatible with initrds.",
-    ):
-        uvm_with_initrd.api.machine_config.patch(
-            huge_pages=HugePagesConfig.HUGETLBFS_2MB
-        )
+
+    uvm_with_initrd.start()
+    serial = Serial(uvm_with_initrd)
+    serial.open()
+    serial.rx(token="# ")
+    serial.tx("mount |grep rootfs")
+    serial.rx(token=f"rootfs on / type {INITRD_FILESYSTEM}")