[PATCH RFC v2 3/3] rust: percpu: add a rust per-CPU variable test

[Mitchell Levy <levymitchell0@gmail.com>]

Add a short exercise for Rust's per-CPU variable API, modelled after
lib/percpu_test.c

Signed-off-by: Mitchell Levy <levymitchell0@gmail.com>
---
 lib/Kconfig.debug       |   9 ++++
 lib/Makefile            |   1 +
 lib/percpu_test_rust.rs | 119 ++++++++++++++++++++++++++++++++++++++++++++++++
 rust/helpers/percpu.c   |  11 +++++
 4 files changed, 140 insertions(+)

diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index df9587aa5c5e..e9fa12940cf2 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -2425,6 +2425,15 @@ config PERCPU_TEST
 
 	  If unsure, say N.
 
+config PERCPU_TEST_RUST
+	tristate "Rust per cpu operations test"
+	depends on m && DEBUG_KERNEL && RUST
+	help
+	  Enable this option to build a test module which validates Rust per-cpu
+	  operations.
+
+	  If unsure, say N.
+
 config ATOMIC64_SELFTEST
 	tristate "Perform an atomic64_t self-test"
 	help
diff --git a/lib/Makefile b/lib/Makefile
index f07b24ce1b3f..adace4f3ae63 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -289,6 +289,7 @@ obj-$(CONFIG_RBTREE_TEST) += rbtree_test.o
 obj-$(CONFIG_INTERVAL_TREE_TEST) += interval_tree_test.o
 
 obj-$(CONFIG_PERCPU_TEST) += percpu_test.o
+obj-$(CONFIG_PERCPU_TEST_RUST) += percpu_test_rust.o
 
 obj-$(CONFIG_ASN1) += asn1_decoder.o
 obj-$(CONFIG_ASN1_ENCODER) += asn1_encoder.o
diff --git a/lib/percpu_test_rust.rs b/lib/percpu_test_rust.rs
new file mode 100644
index 000000000000..61d8793b1cb0
--- /dev/null
+++ b/lib/percpu_test_rust.rs
@@ -0,0 +1,119 @@
+// SPDX-License-Identifier: GPL-2.0
+//! A simple self test for the rust per-CPU API.
+
+use core::ffi::c_void;
+
+use kernel::{
+    bindings::{on_each_cpu, smp_processor_id},
+    define_per_cpu,
+    percpu::{cpu_guard::*, *},
+    pr_info,
+    prelude::*,
+    unsafe_get_per_cpu,
+};
+
+module! {
+    type: PerCpuTestModule,
+    name: "percpu_test_rust",
+    author: "Mitchell Levy",
+    description: "Test code to exercise the Rust Per CPU variable API",
+    license: "GPL v2",
+}
+
+struct PerCpuTestModule;
+
+define_per_cpu!(PERCPU: i64 = 0);
+define_per_cpu!(UPERCPU: u64 = 0);
+
+impl kernel::Module for PerCpuTestModule {
+    fn init(_module: &'static ThisModule) -> Result<Self, Error> {
+        pr_info!("rust percpu test start\n");
+
+        let mut native: i64 = 0;
+        let mut pcpu: PerCpu<i64> =
+            unsafe { unsafe_get_per_cpu!(PERCPU, CpuGuard::new()).unwrap() };
+        // SAFETY: We only have one PerCpu that points at PERCPU
+        unsafe { pcpu.get(CpuGuard::new()) }.with(|val: &mut i64| {
+            pr_info!("The contents of pcpu are {}", val);
+
+            native += -1;
+            *val += -1;
+            pr_info!("Native: {}, *pcpu: {}\n", native, val);
+            assert!(native == *val && native == -1);
+
+            native += 1;
+            *val += 1;
+            pr_info!("Native: {}, *pcpu: {}\n", native, val);
+            assert!(native == *val && native == 0);
+        });
+
+        let mut unative: u64 = 0;
+        let mut upcpu: PerCpu<u64> =
+            unsafe { unsafe_get_per_cpu!(UPERCPU, CpuGuard::new()).unwrap() };
+
+        // SAFETY: We only have one PerCpu pointing at UPERCPU
+        unsafe { upcpu.get(CpuGuard::new()) }.with(|val: &mut u64| {
+            unative += 1;
+            *val += 1;
+            pr_info!("Unative: {}, *upcpu: {}\n", unative, val);
+            assert!(unative == *val && unative == 1);
+
+            unative = unative.wrapping_add((-1i64) as u64);
+            *val = val.wrapping_add((-1i64) as u64);
+            pr_info!("Unative: {}, *upcpu: {}\n", unative, val);
+            assert!(unative == *val && unative == 0);
+
+            unative = unative.wrapping_add((-1i64) as u64);
+            *val = val.wrapping_add((-1i64) as u64);
+            pr_info!("Unative: {}, *upcpu: {}\n", unative, val);
+            assert!(unative == *val && unative == (-1i64) as u64);
+
+            unative = 0;
+            *val = 0;
+
+            unative = unative.wrapping_sub(1);
+            *val = val.wrapping_sub(1);
+            pr_info!("Unative: {}, *upcpu: {}\n", unative, val);
+            assert!(unative == *val && unative == (-1i64) as u64);
+            assert!(unative == *val && unative == u64::MAX);
+        });
+
+        pr_info!("rust static percpu test done\n");
+
+        pr_info!("rust dynamic percpu test start\n");
+        let mut test: PerCpu<u64> = PerCpu::new().unwrap();
+
+        unsafe {
+            on_each_cpu(Some(inc_percpu), (&raw mut test) as *mut c_void, 0);
+            on_each_cpu(Some(inc_percpu), (&raw mut test) as *mut c_void, 0);
+            on_each_cpu(Some(inc_percpu), (&raw mut test) as *mut c_void, 0);
+            on_each_cpu(Some(inc_percpu), (&raw mut test) as *mut c_void, 1);
+            on_each_cpu(Some(check_percpu), (&raw mut test) as *mut c_void, 1);
+        }
+
+        pr_info!("rust dynamic percpu test done\n");
+
+        // Return Err to unload the module
+        Result::Err(EINVAL)
+    }
+}
+
+unsafe extern "C" fn inc_percpu(info: *mut c_void) {
+    // SAFETY: We know that info is a void *const PerCpu<u64> and PerCpu<u64> is Send.
+    let mut pcpu = unsafe { (&*(info as *const PerCpu<u64>)).clone() };
+    // SAFETY: smp_processor_id has no preconditions
+    pr_info!("Incrementing on {}\n", unsafe { smp_processor_id() });
+
+    // SAFETY: We don't have multiple clones of pcpu in scope
+    unsafe { pcpu.get(CpuGuard::new()) }.with(|val: &mut u64| *val += 1);
+}
+
+unsafe extern "C" fn check_percpu(info: *mut c_void) {
+    // SAFETY: We know that info is a void *const PerCpu<u64> and PerCpu<u64> is Send.
+    let mut pcpu = unsafe { (&*(info as *const PerCpu<u64>)).clone() };
+    // SAFETY: smp_processor_id has no preconditions
+    pr_info!("Asserting on {}\n", unsafe { smp_processor_id() });
+
+    // SAFETY: We don't have multiple clones of pcpu in scope
+    unsafe { pcpu.get(CpuGuard::new()) }.with(|val: &mut u64| assert!(*val == 4));
+}
diff --git a/rust/helpers/percpu.c b/rust/helpers/percpu.c
index a091389f730f..0e9b2fed3ebd 100644
--- a/rust/helpers/percpu.c
+++ b/rust/helpers/percpu.c
@@ -1,9 +1,20 @@
 // SPDX-License-Identifier: GPL-2.0
 
 #include <linux/percpu.h>
+#include <linux/smp.h>
 
 void __percpu *rust_helper_alloc_percpu(size_t sz, size_t align)
 {
 	return __alloc_percpu(sz, align);
 }
 
+void rust_helper_on_each_cpu(smp_call_func_t func, void *info, int wait)
+{
+	on_each_cpu(func, info, wait);
+}
+
+int rust_helper_smp_processor_id(void)
+{
+	return smp_processor_id();
+}
+

-- 
2.34.1