refactor: replace init-paging feature with nanvix-unstable (#1291)

Make init-paging behavior (CoW guest paging) always-on by removing
it from the feature definitions and all cfg gates. Add a new
nanvix-unstable feature that opts out of CoW paging for guests
that manage their own page tables (e.g., Nanvix).

This inverts the polarity: previously you opted IN to init-paging,
now you opt IN to nanvix-unstable to disable it.

Signed-off-by: danbugs <danilochiarlone@gmail.com>

Author: danbugs

Justfile

@@ -84,8 +84,8 @@ test-like-ci config=default-target hypervisor="kvm":
     @# with default features
     just test {{config}}
 
-    @# with only one driver enabled + build-metadata + init-paging
-    just test {{config}} build-metadata,init-paging,{{ if hypervisor == "mshv3" {"mshv3"} else {"kvm"} }}
+    @# with only one driver enabled + build-metadata
+    just test {{config}} build-metadata,{{ if hypervisor == "mshv3" {"mshv3"} else {"kvm"} }}
 
     @# make sure certain cargo features compile
     just check
@@ -212,31 +212,31 @@ test target=default-target features="": (test-unit target features) (test-isolat
 
 # runs unit tests
 test-unit target=default-target features="":
-    {{ cargo-cmd }} test {{ if features =="" {''} else if features=="no-default-features" {"--no-default-features" } else {"--no-default-features -F init-paging," + features } }} --profile={{ if target == "debug" { "dev" } else { target } }} {{ target-triple-flag }} --lib
+    {{ cargo-cmd }} test {{ if features =="" {''} else if features=="no-default-features" {"--no-default-features" } else {"--no-default-features -F " + features } }} --profile={{ if target == "debug" { "dev" } else { target } }} {{ target-triple-flag }} --lib
 
 # runs tests that requires being run separately, for example due to global state
 test-isolated target=default-target features="" :
-    {{ cargo-cmd }} test {{ if features =="" {''} else if features=="no-default-features" {"--no-default-features" } else {"--no-default-features -F init-paging," + features } }} --profile={{ if target == "debug" { "dev" } else { target } }} {{ target-triple-flag }} -p hyperlight-host --lib -- sandbox::uninitialized::tests::test_log_trace --exact --ignored
-    {{ cargo-cmd }} test {{ if features =="" {''} else if features=="no-default-features" {"--no-default-features" } else {"--no-default-features -F init-paging," + features } }} --profile={{ if target == "debug" { "dev" } else { target } }} {{ target-triple-flag }} -p hyperlight-host --lib -- sandbox::outb::tests::test_log_outb_log --exact --ignored
-    {{ cargo-cmd }} test {{ if features =="" {''} else if features=="no-default-features" {"--no-default-features" } else {"--no-default-features -F init-paging," + features } }} --profile={{ if target == "debug" { "dev" } else { target } }} {{ target-triple-flag }} -p hyperlight-host --test integration_test -- log_message --exact --ignored
+    {{ cargo-cmd }} test {{ if features =="" {''} else if features=="no-default-features" {"--no-default-features" } else {"--no-default-features -F " + features } }} --profile={{ if target == "debug" { "dev" } else { target } }} {{ target-triple-flag }} -p hyperlight-host --lib -- sandbox::uninitialized::tests::test_log_trace --exact --ignored
+    {{ cargo-cmd }} test {{ if features =="" {''} else if features=="no-default-features" {"--no-default-features" } else {"--no-default-features -F " + features } }} --profile={{ if target == "debug" { "dev" } else { target } }} {{ target-triple-flag }} -p hyperlight-host --lib -- sandbox::outb::tests::test_log_outb_log --exact --ignored
+    {{ cargo-cmd }} test {{ if features =="" {''} else if features=="no-default-features" {"--no-default-features" } else {"--no-default-features -F " + features } }} --profile={{ if target == "debug" { "dev" } else { target } }} {{ target-triple-flag }} -p hyperlight-host --test integration_test -- log_message --exact --ignored
     @# metrics tests
-    {{ cargo-cmd }} test {{ if features =="" {''} else if features=="no-default-features" {"--no-default-features" } else {"--no-default-features -F function_call_metrics,init-paging," + features } }} --profile={{ if target == "debug" { "dev" } else { target } }} {{ target-triple-flag }} -p hyperlight-host --lib -- metrics::tests::test_metrics_are_emitted --exact 
+    {{ cargo-cmd }} test {{ if features =="" {''} else if features=="no-default-features" {"--no-default-features" } else {"--no-default-features -F function_call_metrics," + features } }} --profile={{ if target == "debug" { "dev" } else { target } }} {{ target-triple-flag }} -p hyperlight-host --lib -- metrics::tests::test_metrics_are_emitted --exact
 
 # runs integration tests
 test-integration target=default-target features="":
     @# run execute_on_heap test with feature "executable_heap" on (runs with off during normal tests)
-    {{ cargo-cmd }} test {{ if features =="" {"--features executable_heap"} else if features=="no-default-features" {"--no-default-features --features executable_heap"} else {"--no-default-features -F init-paging,executable_heap," + features } }} --profile={{ if target == "debug" { "dev" } else { target } }} {{ target-triple-flag }} --test integration_test execute_on_heap
+    {{ cargo-cmd }} test {{ if features =="" {"--features executable_heap"} else if features=="no-default-features" {"--no-default-features --features executable_heap"} else {"--no-default-features -F executable_heap," + features } }} --profile={{ if target == "debug" { "dev" } else { target } }} {{ target-triple-flag }} --test integration_test execute_on_heap
 
     @# run the rest of the integration tests
-    {{ cargo-cmd }} test -p hyperlight-host {{ if features =="" {''} else if features=="no-default-features" {"--no-default-features" } else {"--no-default-features -F init-paging," + features } }} --profile={{ if target == "debug" { "dev" } else { target } }} {{ target-triple-flag }} --test '*'
+    {{ cargo-cmd }} test -p hyperlight-host {{ if features =="" {''} else if features=="no-default-features" {"--no-default-features" } else {"--no-default-features -F " + features } }} --profile={{ if target == "debug" { "dev" } else { target } }} {{ target-triple-flag }} --test '*'
 
 # tests compilation with no default features on different platforms
 test-compilation-no-default-features target=default-target:
     @# Linux should fail without a hypervisor feature (kvm or mshv3)
     {{ if os() == "linux" { "! " + cargo-cmd + " check -p hyperlight-host --no-default-features "+target-triple-flag+" 2> /dev/null" } else { "" } }}
     @# Windows should succeed even without default features
     {{ if os() == "windows" { cargo-cmd + " check -p hyperlight-host --no-default-features" } else { "" } }}
-    @# Linux should succeed with a hypervisor driver but without init-paging
+    @# Linux should succeed with a hypervisor driver but without default features
     {{ if os() == "linux" { cargo-cmd + " check -p hyperlight-host --no-default-features --features kvm" } else { "" } }}  {{ target-triple-flag }}
     {{ if os() == "linux" { cargo-cmd + " check -p hyperlight-host --no-default-features --features mshv3" } else { "" } }}  {{ target-triple-flag }}
 

src/hyperlight_common/Cargo.toml

@@ -31,7 +31,7 @@ fuzzing = ["dep:arbitrary"]
 trace_guest = []
 mem_profile = []
 std = ["thiserror/std", "log/std", "tracing/std"]
-init-paging = []
+nanvix-unstable = []
 
 [lib]
 bench = false # see https://bheisler.github.io/criterion.rs/book/faq.html#cargo-bench-gives-unrecognized-option-errors-for-valid-command-line-options

src/hyperlight_guest_bin/Cargo.toml

@@ -23,7 +23,7 @@ macros = ["dep:hyperlight-guest-macro", "dep:linkme"]
 
 [dependencies]
 hyperlight-guest = { workspace = true, default-features = false }
-hyperlight-common = { workspace = true, default-features = false, features = [ "init-paging" ] }
+hyperlight-common = { workspace = true, default-features = false }
 hyperlight-guest-tracing = { workspace = true, default-features = false }
 hyperlight-guest-macro = { workspace = true, default-features = false, optional = true }
 buddy_system_allocator = "0.12.0"

src/hyperlight_host/Cargo.toml

@@ -40,7 +40,7 @@ tracing = { version = "0.1.44", features = ["log"] }
 tracing-log = "0.2.0"
 tracing-core = "0.1.36"
 tracing-opentelemetry = { version = "0.32.1", optional = true }
-hyperlight-common = { workspace = true, default-features = true, features = [ "std", "init-paging" ] }
+hyperlight-common = { workspace = true, default-features = true, features = [ "std" ] }
 hyperlight-guest-tracing = { workspace = true, default-features = true, optional = true }
 vmm-sys-util = "0.15.0"
 crossbeam-channel = "0.5.15"
@@ -122,7 +122,7 @@ cfg_aliases = "0.2.1"
 built = { version = "0.8.0", optional = true, features = ["chrono", "git2"] }
 
 [features]
-default = ["kvm", "mshv3", "build-metadata", "init-paging"]
+default = ["kvm", "mshv3", "build-metadata"]
 function_call_metrics = []
 executable_heap = []
 # This feature enables printing of debug information to stdout in debug builds
@@ -137,7 +137,7 @@ mshv3 = ["dep:mshv-bindings", "dep:mshv-ioctls"]
 gdb = ["dep:gdbstub", "dep:gdbstub_arch"]
 fuzzing = ["hyperlight-common/fuzzing"]
 build-metadata = ["dep:built"]
-init-paging = []
+nanvix-unstable = []
 
 [[bench]]
 name = "benchmarks"

src/hyperlight_host/src/hypervisor/hyperlight_vm.rs

@@ -443,10 +443,10 @@ impl HyperlightVm {
             None => return Err(CreateHyperlightVmError::NoHypervisorFound),
         };
 
-        #[cfg(feature = "init-paging")]
+        #[cfg(not(feature = "nanvix-unstable"))]
         vm.set_sregs(&CommonSpecialRegisters::standard_64bit_defaults(_pml4_addr))
             .map_err(VmError::Register)?;
-        #[cfg(not(feature = "init-paging"))]
+        #[cfg(feature = "nanvix-unstable")]
         vm.set_sregs(&CommonSpecialRegisters::standard_real_mode_defaults())
             .map_err(VmError::Register)?;
 
@@ -691,16 +691,16 @@ impl HyperlightVm {
 
     /// Get the current base page table physical address.
     ///
-    /// With `init-paging`, reads CR3 from the vCPU special registers.
-    /// Without `init-paging`, returns 0 (identity-mapped, no page tables).
+    /// By default, reads CR3 from the vCPU special registers.
+    /// With `nanvix-unstable`, returns 0 (identity-mapped, no page tables).
     pub(crate) fn get_root_pt(&self) -> Result<u64, AccessPageTableError> {
-        #[cfg(feature = "init-paging")]
+        #[cfg(not(feature = "nanvix-unstable"))]
         {
             let sregs = self.vm.sregs()?;
             // Mask off the flags bits
             Ok(sregs.cr3 & !0xfff_u64)
         }
-        #[cfg(not(feature = "init-paging"))]
+        #[cfg(feature = "nanvix-unstable")]
         {
             Ok(0)
         }
@@ -1043,7 +1043,7 @@ impl HyperlightVm {
         self.vm.set_debug_regs(&CommonDebugRegs::default())?;
         self.vm.reset_xsave()?;
 
-        #[cfg(feature = "init-paging")]
+        #[cfg(not(feature = "nanvix-unstable"))]
         {
             // Restore the full special registers from snapshot, but update CR3
             // to point to the new (relocated) page tables
@@ -1052,11 +1052,11 @@ impl HyperlightVm {
             self.pending_tlb_flush = true;
             self.vm.set_sregs(&sregs)?;
         }
-        #[cfg(not(feature = "init-paging"))]
+        #[cfg(feature = "nanvix-unstable")]
         {
             let _ = (cr3, sregs); // suppress unused warnings
             // TODO: This is probably not correct.
-            // Let's deal with it when we clean up the init-paging feature
+            // Let's deal with it when we clean up the nanvix-unstable feature
             self.vm
                 .set_sregs(&CommonSpecialRegisters::standard_real_mode_defaults())?;
         }
@@ -1591,7 +1591,7 @@ mod debug {
 }
 
 #[cfg(test)]
-#[cfg(feature = "init-paging")]
+#[cfg(not(feature = "nanvix-unstable"))]
 #[allow(clippy::needless_range_loop)]
 mod tests {
     use std::sync::{Arc, Mutex};

src/hyperlight_host/src/hypervisor/regs/special_regs.rs

@@ -28,7 +28,7 @@ use windows::Win32::System::Hypervisor::*;
 use super::FromWhpRegisterError;
 
 cfg_if::cfg_if! {
-    if #[cfg(feature = "init-paging")] {
+    if #[cfg(not(feature = "nanvix-unstable"))] {
         pub(crate) const CR4_PAE: u64 = 1 << 5;
         pub(crate) const CR4_OSFXSR: u64 = 1 << 9;
         pub(crate) const CR4_OSXMMEXCPT: u64 = 1 << 10;
@@ -69,7 +69,7 @@ pub(crate) struct CommonSpecialRegisters {
 }
 
 impl CommonSpecialRegisters {
-    #[cfg(feature = "init-paging")]
+    #[cfg(not(feature = "nanvix-unstable"))]
     pub(crate) fn standard_64bit_defaults(pml4_addr: u64) -> Self {
         CommonSpecialRegisters {
             cs: CommonSegmentRegister {
@@ -104,7 +104,7 @@ impl CommonSpecialRegisters {
         }
     }
 
-    #[cfg(not(feature = "init-paging"))]
+    #[cfg(feature = "nanvix-unstable")]
     pub(crate) fn standard_real_mode_defaults() -> Self {
         CommonSpecialRegisters {
             cs: CommonSegmentRegister {

src/hyperlight_host/src/hypervisor/virtual_machine/kvm.rs

@@ -33,7 +33,7 @@ use crate::hypervisor::regs::{
     CommonDebugRegs, CommonFpu, CommonRegisters, CommonSpecialRegisters, FP_CONTROL_WORD_DEFAULT,
     MXCSR_DEFAULT,
 };
-#[cfg(all(test, feature = "init-paging"))]
+#[cfg(all(test, not(feature = "nanvix-unstable")))]
 use crate::hypervisor::virtual_machine::XSAVE_BUFFER_SIZE;
 use crate::hypervisor::virtual_machine::{
     CreateVmError, MapMemoryError, RegisterError, RunVcpuError, UnmapMemoryError, VirtualMachine,
@@ -305,7 +305,7 @@ impl VirtualMachine for KvmVm {
     }
 
     #[cfg(test)]
-    #[cfg(feature = "init-paging")]
+    #[cfg(not(feature = "nanvix-unstable"))]
     fn set_xsave(&self, xsave: &[u32]) -> std::result::Result<(), RegisterError> {
         if std::mem::size_of_val(xsave) != XSAVE_BUFFER_SIZE {
             return Err(RegisterError::XsaveSizeMismatch {

src/hyperlight_host/src/hypervisor/virtual_machine/mod.rs

@@ -108,7 +108,7 @@ pub(crate) const XSAVE_MIN_SIZE: usize = 576;
 
 /// Standard XSAVE buffer size (4KB) used by KVM and MSHV.
 /// WHP queries the required size dynamically.
-#[cfg(all(any(kvm, mshv3), test, feature = "init-paging"))]
+#[cfg(all(any(kvm, mshv3), test, not(feature = "nanvix-unstable")))]
 pub(crate) const XSAVE_BUFFER_SIZE: usize = 4096;
 
 // Compiler error if no hypervisor type is available
@@ -341,7 +341,7 @@ pub(crate) trait VirtualMachine: Debug + Send {
     fn reset_xsave(&self) -> std::result::Result<(), RegisterError>;
     /// Set xsave - only used for tests
     #[cfg(test)]
-    #[cfg(feature = "init-paging")]
+    #[cfg(not(feature = "nanvix-unstable"))]
     fn set_xsave(&self, xsave: &[u32]) -> std::result::Result<(), RegisterError>;
 
     /// Get partition handle

src/hyperlight_host/src/hypervisor/virtual_machine/mshv.rs

@@ -39,7 +39,7 @@ use crate::hypervisor::regs::{
     CommonDebugRegs, CommonFpu, CommonRegisters, CommonSpecialRegisters, FP_CONTROL_WORD_DEFAULT,
     MXCSR_DEFAULT,
 };
-#[cfg(all(test, feature = "init-paging"))]
+#[cfg(all(test, not(feature = "nanvix-unstable")))]
 use crate::hypervisor::virtual_machine::XSAVE_BUFFER_SIZE;
 use crate::hypervisor::virtual_machine::{
     CreateVmError, MapMemoryError, RegisterError, RunVcpuError, UnmapMemoryError, VirtualMachine,
@@ -330,7 +330,7 @@ impl VirtualMachine for MshvVm {
     }
 
     #[cfg(test)]
-    #[cfg(feature = "init-paging")]
+    #[cfg(not(feature = "nanvix-unstable"))]
     fn set_xsave(&self, xsave: &[u32]) -> std::result::Result<(), RegisterError> {
         if std::mem::size_of_val(xsave) != XSAVE_BUFFER_SIZE {
             return Err(RegisterError::XsaveSizeMismatch {

src/hyperlight_host/src/hypervisor/virtual_machine/whp.rs

@@ -581,7 +581,7 @@ impl VirtualMachine for WhpVm {
     }
 
     #[cfg(test)]
-    #[cfg(feature = "init-paging")]
+    #[cfg(not(feature = "nanvix-unstable"))]
     fn set_xsave(&self, xsave: &[u32]) -> std::result::Result<(), RegisterError> {
         // Get the required buffer size by calling with NULL buffer.
         // If the buffer is not large enough (0 won't be), WHvGetVirtualProcessorXsaveState returns