Implement per-CPU variables via CPU-local storage (#917)

* Only supported on x86_64 currently; aarch64 support to come.

* x86_64 implementation is based on the GS segment register
  and the GsBase MSR, as typically used on other OSes.

* Tested working, but not yet used anywhere in Theseus.

Co-authored-by: Klim Tsoutsman <[email protected]>

Author: kevinaboos

Cargo.lock

@@ -16,6 +16,7 @@ scheduler = { path = "../scheduler" }
 spawn = { path = "../spawn" }
 kernel_config = { path = "../kernel_config" }
 cpu = { path = "../cpu" }
+per_cpu = { path = "../per_cpu" }
 no_drop = { path = "../no_drop" }
 early_tls = { path = "../early_tls" }
 

kernel/ap_start/Cargo.toml

@@ -106,7 +106,11 @@ pub fn kstart_ap(
     }
 
     // Now that the Local APIC has been initialized for this CPU, we can initialize the
-    // task management subsystem and create the idle task for this CPU.
+    // per-CPU storage, tasking, and create the idle task for this CPU.
+
+    #[cfg(target_arch = "x86_64")] // not yet supported on aarch64
+    per_cpu::init(cpu_id).unwrap();
+
     let bootstrap_task = spawn::init(kernel_mmi_ref.clone(), cpu_id, this_ap_stack).unwrap();
     spawn::create_idle_task().unwrap();
 

kernel/ap_start/src/lib.rs

@@ -23,6 +23,7 @@ spawn = { path = "../spawn" }
 stack = { path = "../stack" }
 task = { path = "../task" }
 cpu = { path = "../cpu" }
+per_cpu = { path = "../per_cpu" }
 
 [target.'cfg(target_arch = "x86_64")'.dependencies]
 logger_x86_64 = { path = "../logger_x86_64" }

kernel/captain/Cargo.toml

@@ -121,6 +121,8 @@ pub fn init(
 
     // get BSP's CPU ID
     let bsp_id = cpu::bootstrap_cpu().ok_or("captain::init(): couldn't get ID of bootstrap CPU!")?;
+    #[cfg(target_arch = "x86_64")] // not yet supported on aarch64
+    per_cpu::init(bsp_id)?;
 
     // Initialize the scheduler and create the initial `Task`,
     // which is bootstrapped from this current execution context.

kernel/captain/src/lib.rs

@@ -0,0 +1,18 @@
+[package]
+authors = ["Kevin Boos <[email protected]>"]
+name = "cpu_local"
+description = "Support for accessing CPU-local storage via per-CPU variables"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
+crossbeam-utils = { version = "0.8.12", default-features = false }
+log = "0.4.8"
+spin = "0.9.0"
+
+irq_safety = { git = "https://github.com/theseus-os/irq_safety" }
+memory = { path = "../memory" }
+preemption = { path = "../preemption" }
+
+[target.'cfg(target_arch = "x86_64")'.dependencies]
+x86_64 = "0.14.8"