Rust support

index f18e6dfc68c5..52f5488c61bc 100644
@@ -206,7 +206,7 @@ static struct sym_entry *read_symbol(FILE *in)
 
 	rc = fscanf(in, "%llx %c %499s\n", &addr, &type, name);
 	if (rc != 3) {
-		if (rc != EOF && fgets(name, 500, in) == NULL)
+		if (rc != EOF && fgets(name, sizeof(name), in) == NULL)
 			fprintf(stderr, "Read error or end of file.\n");
 		return NULL;
 	}

index 52f5488c61bc..f3c5a2623f71 100644
@@ -27,8 +27,14 @@
 
 #define ARRAY_SIZE(arr) (sizeof(arr) / sizeof(arr[0]))
 
+#define _stringify_1(x)	#x
+#define _stringify(x)	_stringify_1(x)
+
 #define KSYM_NAME_LEN		128
 
+/* A substantially bigger size than the current maximum. */
+#define KSYM_NAME_LEN_BUFFER	499
+
 struct sym_entry {
 	unsigned long long addr;
 	unsigned int len;

@@ -198,13 +204,13 @@ static void check_symbol_range(const char *sym, unsigned long long addr,
 
 static struct sym_entry *read_symbol(FILE *in)
 {
-	char name[500], type;
+	char name[KSYM_NAME_LEN_BUFFER+1], type;
 	unsigned long long addr;
 	unsigned int len;
 	struct sym_entry *sym;
 	int rc;
 
-	rc = fscanf(in, "%llx %c %499s\n", &addr, &type, name);
+	rc = fscanf(in, "%llx %c %" _stringify(KSYM_NAME_LEN_BUFFER) "s\n", &addr, &type, name);
 	if (rc != 3) {
 		if (rc != EOF && fgets(name, sizeof(name), in) == NULL)
 			fprintf(stderr, "Read error or end of file.\n");

index f3c5a2623f71..f543b1c4f99f 100644
@@ -33,7 +33,11 @@
 #define KSYM_NAME_LEN		128
 
 /* A substantially bigger size than the current maximum. */
-#define KSYM_NAME_LEN_BUFFER	499
+#define KSYM_NAME_LEN_BUFFER	512
+_Static_assert(
+	KSYM_NAME_LEN_BUFFER == KSYM_NAME_LEN * 4,
+	"Please keep KSYM_NAME_LEN_BUFFER in sync with KSYM_NAME_LEN"
+);
 
 struct sym_entry {
 	unsigned long long addr;

index fbdf8d3279ac..87e2b1638115 100644
@@ -70,12 +70,20 @@ static unsigned int kallsyms_expand_symbol(unsigned int off,
 	data = &kallsyms_names[off];
 	len = *data;
 	data++;
+	off++;
+
+	/* If MSB is 1, it is a "big" symbol, so needs an additional byte. */
+	if ((len & 0x80) != 0) {
+		len = (len & 0x7F) | (*data << 7);
+		data++;
+		off++;
+	}
 
 	/*
 	 * Update the offset to return the offset for the next symbol on
 	 * the compressed stream.
 	 */
-	off += len + 1;
+	off += len;
 
 	/*
 	 * For every byte on the compressed symbol data, copy the table

@@ -128,7 +136,7 @@ static char kallsyms_get_symbol_type(unsigned int off)
 static unsigned int get_symbol_offset(unsigned long pos)
 {
 	const u8 *name;
-	int i;
+	int i, len;
 
 	/*
 	 * Use the closest marker we have. We have markers every 256 positions,

@@ -142,8 +150,18 @@ static unsigned int get_symbol_offset(unsigned long pos)
 	 * so we just need to add the len to the current pointer for every
 	 * symbol we wish to skip.
 	 */
-	for (i = 0; i < (pos & 0xFF); i++)
-		name = name + (*name) + 1;
+	for (i = 0; i < (pos & 0xFF); i++) {
+		len = *name;
+
+		/*
+		 * If MSB is 1, it is a "big" symbol, so we need to look into
+		 * the next byte (and skip it, too).
+		 */
+		if ((len & 0x80) != 0)
+			len = ((len & 0x7F) | (name[1] << 7)) + 1;
+
+		name = name + len + 1;
+	}
 
 	return name - kallsyms_names;
 }

index f543b1c4f99f..9da3b7767e9d 100644
@@ -481,12 +481,35 @@ static void write_src(void)
 		if ((i & 0xFF) == 0)
 			markers[i >> 8] = off;
 
-		printf("\t.byte 0x%02x", table[i]->len);
+		/* There cannot be any symbol of length zero. */
+		if (table[i]->len == 0) {
+			fprintf(stderr, "kallsyms failure: "
+				"unexpected zero symbol length\n");
+			exit(EXIT_FAILURE);
+		}
+
+		/* Only lengths that fit in up-to-two-byte ULEB128 are supported. */
+		if (table[i]->len > 0x3FFF) {
+			fprintf(stderr, "kallsyms failure: "
+				"unexpected huge symbol length\n");
+			exit(EXIT_FAILURE);
+		}
+
+		/* Encode length with ULEB128. */
+		if (table[i]->len <= 0x7F) {
+			/* Most symbols use a single byte for the length. */
+			printf("\t.byte 0x%02x", table[i]->len);
+			off += table[i]->len + 1;
+		} else {
+			/* "Big" symbols use two bytes. */
+			printf("\t.byte 0x%02x, 0x%02x",
+				(table[i]->len & 0x7F) | 0x80,
+				(table[i]->len >> 7) & 0x7F);
+			off += table[i]->len + 2;
+		}
 		for (k = 0; k < table[i]->len; k++)
 			printf(", 0x%02x", table[i]->sym[k]);
 		printf("\n");
-
-		off += table[i]->len + 1;
 	}
 	printf("\n");
 

index ad39636e0c3f..649faac31ddb 100644
@@ -15,7 +15,7 @@
 
 #include <asm/sections.h>
 
-#define KSYM_NAME_LEN 128
+#define KSYM_NAME_LEN 512
 #define KSYM_SYMBOL_LEN (sizeof("%s+%#lx/%#lx [%s %s]") + \
 			(KSYM_NAME_LEN - 1) + \
 			2*(BITS_PER_LONG*3/10) + (MODULE_NAME_LEN - 1) + \

index bc475e62279d..ec06ce59d728 100644
@@ -213,7 +213,7 @@ static int klp_resolve_symbols(Elf_Shdr *sechdrs, const char *strtab,
 	 * we use the smallest/strictest upper bound possible (56, based on
 	 * the current definition of MODULE_NAME_LEN) to prevent overflows.
 	 */
-	BUILD_BUG_ON(MODULE_NAME_LEN < 56 || KSYM_NAME_LEN != 128);
+	BUILD_BUG_ON(MODULE_NAME_LEN < 56 || KSYM_NAME_LEN != 512);
 
 	relas = (Elf_Rela *) relasec->sh_addr;
 	/* For each rela in this klp relocation section */

@@ -227,7 +227,7 @@ static int klp_resolve_symbols(Elf_Shdr *sechdrs, const char *strtab,
 
 		/* Format: .klp.sym.sym_objname.sym_name,sympos */
 		cnt = sscanf(strtab + sym->st_name,
-			     ".klp.sym.%55[^.].%127[^,],%lu",
+			     ".klp.sym.%55[^.].%511[^,],%lu",
 			     sym_objname, sym_name, &sympos);
 		if (cnt != 3) {
 			pr_err("symbol %s has an incorrectly formatted name\n",

index 9da3b7767e9d..3b64dda7e4cc 100644
@@ -30,10 +30,10 @@
 #define _stringify_1(x)	#x
 #define _stringify(x)	_stringify_1(x)
 
-#define KSYM_NAME_LEN		128
+#define KSYM_NAME_LEN		512
 
 /* A substantially bigger size than the current maximum. */
-#define KSYM_NAME_LEN_BUFFER	512
+#define KSYM_NAME_LEN_BUFFER	2048
 _Static_assert(
 	KSYM_NAME_LEN_BUFFER == KSYM_NAME_LEN * 4,
 	"Please keep KSYM_NAME_LEN_BUFFER in sync with KSYM_NAME_LEN"

index efb6c3f5f2a9..5a37ccbec54f 100644
@@ -6,7 +6,7 @@
 #include <stdio.h>
 #include <unistd.h>
 
-#define KSYM_NAME_LEN 128
+#define KSYM_NAME_LEN 512
 
 struct module;
 

index e7758707cadd..116a80c31675 100644
@@ -95,7 +95,7 @@ struct perf_record_throttle {
 };
 
 #ifndef KSYM_NAME_LEN
-#define KSYM_NAME_LEN 256
+#define KSYM_NAME_LEN 512
 #endif
 
 struct perf_record_ksymbol {

index 72ab9870454b..542f9b059c3b 100644
@@ -7,7 +7,7 @@
 #include <linux/types.h>
 
 #ifndef KSYM_NAME_LEN
-#define KSYM_NAME_LEN 256
+#define KSYM_NAME_LEN 512
 #endif
 
 static inline u8 kallsyms2elf_binding(char type)

new file mode 100644
index 000000000000..b4f15eee2ffd
@@ -0,0 +1,51 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Non-trivial C macros cannot be used in Rust. Similarly, inlined C functions
+ * cannot be called either. This file explicitly creates functions ("helpers")
+ * that wrap those so that they can be called from Rust.
+ *
+ * Even though Rust kernel modules should never use directly the bindings, some
+ * of these helpers need to be exported because Rust generics and inlined
+ * functions may not get their code generated in the crate where they are
+ * defined. Other helpers, called from non-inline functions, may not be
+ * exported, in principle. However, in general, the Rust compiler does not
+ * guarantee codegen will be performed for a non-inline function either.
+ * Therefore, this file exports all the helpers. In the future, this may be
+ * revisited to reduce the number of exports after the compiler is informed
+ * about the places codegen is required.
+ *
+ * All symbols are exported as GPL-only to guarantee no GPL-only feature is
+ * accidentally exposed.
+ */
+
+#include <linux/bug.h>
+#include <linux/build_bug.h>
+
+__noreturn void rust_helper_BUG(void)
+{
+	BUG();
+}
+EXPORT_SYMBOL_GPL(rust_helper_BUG);
+
+/*
+ * We use `bindgen`'s `--size_t-is-usize` option to bind the C `size_t` type
+ * as the Rust `usize` type, so we can use it in contexts where Rust
+ * expects a `usize` like slice (array) indices. `usize` is defined to be
+ * the same as C's `uintptr_t` type (can hold any pointer) but not
+ * necessarily the same as `size_t` (can hold the size of any single
+ * object). Most modern platforms use the same concrete integer type for
+ * both of them, but in case we find ourselves on a platform where
+ * that's not true, fail early instead of risking ABI or
+ * integer-overflow issues.
+ *
+ * If your platform fails this assertion, it means that you are in
+ * danger of integer-overflow bugs (even if you attempt to remove
+ * `--size_t-is-usize`). It may be easiest to change the kernel ABI on
+ * your platform such that `size_t` matches `uintptr_t` (i.e., to increase
+ * `size_t`, because `uintptr_t` has to be at least as big as `size_t`).
+ */
+static_assert(
+	sizeof(size_t) == sizeof(uintptr_t) &&
+	__alignof__(size_t) == __alignof__(uintptr_t),
+	"Rust code expects C `size_t` to match Rust `usize`"
+);

new file mode 100644
index 000000000000..6162b5c6d4c9
@@ -0,0 +1,438 @@
+//! Memory allocation APIs
+
+#![stable(feature = "alloc_module", since = "1.28.0")]
+
+#[cfg(not(test))]
+use core::intrinsics;
+use core::intrinsics::{min_align_of_val, size_of_val};
+
+use core::ptr::Unique;
+#[cfg(not(test))]
+use core::ptr::{self, NonNull};
+
+#[stable(feature = "alloc_module", since = "1.28.0")]
+#[doc(inline)]
+pub use core::alloc::*;
+
+use core::marker::Destruct;
+
+#[cfg(test)]
+mod tests;
+
+extern "Rust" {
+    // These are the magic symbols to call the global allocator.  rustc generates
+    // them to call `__rg_alloc` etc. if there is a `#[global_allocator]` attribute
+    // (the code expanding that attribute macro generates those functions), or to call
+    // the default implementations in libstd (`__rdl_alloc` etc. in `library/std/src/alloc.rs`)
+    // otherwise.
+    // The rustc fork of LLVM also special-cases these function names to be able to optimize them
+    // like `malloc`, `realloc`, and `free`, respectively.
+    #[rustc_allocator]
+    #[rustc_allocator_nounwind]
+    fn __rust_alloc(size: usize, align: usize) -> *mut u8;
+    #[rustc_allocator_nounwind]
+    fn __rust_dealloc(ptr: *mut u8, size: usize, align: usize);
+    #[rustc_allocator_nounwind]
+    fn __rust_realloc(ptr: *mut u8, old_size: usize, align: usize, new_size: usize) -> *mut u8;
+    #[rustc_allocator_nounwind]
+    fn __rust_alloc_zeroed(size: usize, align: usize) -> *mut u8;
+}
+
+/// The global memory allocator.
+///
+/// This type implements the [`Allocator`] trait by forwarding calls
+/// to the allocator registered with the `#[global_allocator]` attribute
+/// if there is one, or the `std` crate’s default.
+///
+/// Note: while this type is unstable, the functionality it provides can be
+/// accessed through the [free functions in `alloc`](self#functions).
+#[unstable(feature = "allocator_api", issue = "32838")]
+#[derive(Copy, Clone, Default, Debug)]
+#[cfg(not(test))]
+pub struct Global;
+
+#[cfg(test)]
+pub use std::alloc::Global;
+
+/// Allocate memory with the global allocator.
+///
+/// This function forwards calls to the [`GlobalAlloc::alloc`] method
+/// of the allocator registered with the `#[global_allocator]` attribute
+/// if there is one, or the `std` crate’s default.
+///
+/// This function is expected to be deprecated in favor of the `alloc` method
+/// of the [`Global`] type when it and the [`Allocator`] trait become stable.
+///
+/// # Safety
+///
+/// See [`GlobalAlloc::alloc`].
+///
+/// # Examples
+///
+/// ```
+/// use std::alloc::{alloc, dealloc, Layout};
+///
+/// unsafe {
+///     let layout = Layout::new::<u16>();
+///     let ptr = alloc(layout);
+///
+///     *(ptr as *mut u16) = 42;
+///     assert_eq!(*(ptr as *mut u16), 42);
+///
+///     dealloc(ptr, layout);
+/// }
+/// ```
+#[stable(feature = "global_alloc", since = "1.28.0")]
+#[must_use = "losing the pointer will leak memory"]
+#[inline]
+pub unsafe fn alloc(layout: Layout) -> *mut u8 {
+    unsafe { __rust_alloc(layout.size(), layout.align()) }
+}
+
+/// Deallocate memory with the global allocator.
+///
+/// This function forwards calls to the [`GlobalAlloc::dealloc`] method
+/// of the allocator registered with the `#[global_allocator]` attribute
+/// if there is one, or the `std` crate’s default.
+///
+/// This function is expected to be deprecated in favor of the `dealloc` method
+/// of the [`Global`] type when it and the [`Allocator`] trait become stable.
+///
+/// # Safety
+///
+/// See [`GlobalAlloc::dealloc`].
+#[stable(feature = "global_alloc", since = "1.28.0")]
+#[inline]
+pub unsafe fn dealloc(ptr: *mut u8, layout: Layout) {
+    unsafe { __rust_dealloc(ptr, layout.size(), layout.align()) }
+}
+
+/// Reallocate memory with the global allocator.
+///
+/// This function forwards calls to the [`GlobalAlloc::realloc`] method
+/// of the allocator registered with the `#[global_allocator]` attribute
+/// if there is one, or the `std` crate’s default.
+///
+/// This function is expected to be deprecated in favor of the `realloc` method
+/// of the [`Global`] type when it and the [`Allocator`] trait become stable.
+///
+/// # Safety
+///
+/// See [`GlobalAlloc::realloc`].
+#[stable(feature = "global_alloc", since = "1.28.0")]
+#[must_use = "losing the pointer will leak memory"]
+#[inline]
+pub unsafe fn realloc(ptr: *mut u8, layout: Layout, new_size: usize) -> *mut u8 {
+    unsafe { __rust_realloc(ptr, layout.size(), layout.align(), new_size) }
+}
+
+/// Allocate zero-initialized memory with the global allocator.
+///
+/// This function forwards calls to the [`GlobalAlloc::alloc_zeroed`] method
+/// of the allocator registered with the `#[global_allocator]` attribute
+/// if there is one, or the `std` crate’s default.
+///
+/// This function is expected to be deprecated in favor of the `alloc_zeroed` method
+/// of the [`Global`] type when it and the [`Allocator`] trait become stable.
+///
+/// # Safety
+///
+/// See [`GlobalAlloc::alloc_zeroed`].
+///
+/// # Examples
+///
+/// ```
+/// use std::alloc::{alloc_zeroed, dealloc, Layout};
+///
+/// unsafe {
+///     let layout = Layout::new::<u16>();
+///     let ptr = alloc_zeroed(layout);
+///
+///     assert_eq!(*(ptr as *mut u16), 0);
+///
+///     dealloc(ptr, layout);
+/// }
+/// ```
+#[stable(feature = "global_alloc", since = "1.28.0")]
+#[must_use = "losing the pointer will leak memory"]
+#[inline]
+pub unsafe fn alloc_zeroed(layout: Layout) -> *mut u8 {
+    unsafe { __rust_alloc_zeroed(layout.size(), layout.align()) }
+}
+
+#[cfg(not(test))]
+impl Global {
+    #[inline]
+    fn alloc_impl(&self, layout: Layout, zeroed: bool) -> Result<NonNull<[u8]>, AllocError> {
+        match layout.size() {
+            0 => Ok(NonNull::slice_from_raw_parts(layout.dangling(), 0)),
+            // SAFETY: `layout` is non-zero in size,
+            size => unsafe {
+                let raw_ptr = if zeroed { alloc_zeroed(layout) } else { alloc(layout) };
+                let ptr = NonNull::new(raw_ptr).ok_or(AllocError)?;
+                Ok(NonNull::slice_from_raw_parts(ptr, size))
+            },
+        }
+    }
+
+    // SAFETY: Same as `Allocator::grow`
+    #[inline]
+    unsafe fn grow_impl(
+        &self,
+        ptr: NonNull<u8>,
+        old_layout: Layout,
+        new_layout: Layout,
+        zeroed: bool,
+    ) -> Result<NonNull<[u8]>, AllocError> {
+        debug_assert!(
+            new_layout.size() >= old_layout.size(),
+            "`new_layout.size()` must be greater than or equal to `old_layout.size()`"
+        );
+
+        match old_layout.size() {
+            0 => self.alloc_impl(new_layout, zeroed),
+
+            // SAFETY: `new_size` is non-zero as `old_size` is greater than or equal to `new_size`
+            // as required by safety conditions. Other conditions must be upheld by the caller
+            old_size if old_layout.align() == new_layout.align() => unsafe {
+                let new_size = new_layout.size();
+
+                // `realloc` probably checks for `new_size >= old_layout.size()` or something similar.
+                intrinsics::assume(new_size >= old_layout.size());
+
+                let raw_ptr = realloc(ptr.as_ptr(), old_layout, new_size);
+                let ptr = NonNull::new(raw_ptr).ok_or(AllocError)?;
+                if zeroed {
+                    raw_ptr.add(old_size).write_bytes(0, new_size - old_size);
+                }
+                Ok(NonNull::slice_from_raw_parts(ptr, new_size))
+            },
+
+            // SAFETY: because `new_layout.size()` must be greater than or equal to `old_size`,
+            // both the old and new memory allocation are valid for reads and writes for `old_size`
+            // bytes. Also, because the old allocation wasn't yet deallocated, it cannot overlap
+            // `new_ptr`. Thus, the call to `copy_nonoverlapping` is safe. The safety contract
+            // for `dealloc` must be upheld by the caller.
+            old_size => unsafe {
+                let new_ptr = self.alloc_impl(new_layout, zeroed)?;
+                ptr::copy_nonoverlapping(ptr.as_ptr(), new_ptr.as_mut_ptr(), old_size);
+                self.deallocate(ptr, old_layout);
+                Ok(new_ptr)
+            },
+        }
+    }
+}
+
+#[unstable(feature = "allocator_api", issue = "32838")]
+#[cfg(not(test))]
+unsafe impl Allocator for Global {
+    #[inline]
+    fn allocate(&self, layout: Layout) -> Result<NonNull<[u8]>, AllocError> {
+        self.alloc_impl(layout, false)
+    }
+
+    #[inline]
+    fn allocate_zeroed(&self, layout: Layout) -> Result<NonNull<[u8]>, AllocError> {
+        self.alloc_impl(layout, true)
+    }
+
+    #[inline]
+    unsafe fn deallocate(&self, ptr: NonNull<u8>, layout: Layout) {
+        if layout.size() != 0 {
+            // SAFETY: `layout` is non-zero in size,
+            // other conditions must be upheld by the caller
+            unsafe { dealloc(ptr.as_ptr(), layout) }
+        }
+    }
+
+    #[inline]
+    unsafe fn grow(
+        &self,
+        ptr: NonNull<u8>,
+        old_layout: Layout,
+        new_layout: Layout,
+    ) -> Result<NonNull<[u8]>, AllocError> {
+        // SAFETY: all conditions must be upheld by the caller
+        unsafe { self.grow_impl(ptr, old_layout, new_layout, false) }
+    }
+
+    #[inline]
+    unsafe fn grow_zeroed(
+        &self,
+        ptr: NonNull<u8>,
+        old_layout: Layout,
+        new_layout: Layout,
+    ) -> Result<NonNull<[u8]>, AllocError> {
+        // SAFETY: all conditions must be upheld by the caller
+        unsafe { self.grow_impl(ptr, old_layout, new_layout, true) }
+    }
+
+    #[inline]
+    unsafe fn shrink(
+        &self,
+        ptr: NonNull<u8>,
+        old_layout: Layout,
+        new_layout: Layout,
+    ) -> Result<NonNull<[u8]>, AllocError> {
+        debug_assert!(
+            new_layout.size() <= old_layout.size(),
+            "`new_layout.size()` must be smaller than or equal to `old_layout.size()`"
+        );
+
+        match new_layout.size() {
+            // SAFETY: conditions must be upheld by the caller
+            0 => unsafe {
+                self.deallocate(ptr, old_layout);
+                Ok(NonNull::slice_from_raw_parts(new_layout.dangling(), 0))
+            },
+
+            // SAFETY: `new_size` is non-zero. Other conditions must be upheld by the caller
+            new_size if old_layout.align() == new_layout.align() => unsafe {
+                // `realloc` probably checks for `new_size <= old_layout.size()` or something similar.
+                intrinsics::assume(new_size <= old_layout.size());
+
+                let raw_ptr = realloc(ptr.as_ptr(), old_layout, new_size);
+                let ptr = NonNull::new(raw_ptr).ok_or(AllocError)?;
+                Ok(NonNull::slice_from_raw_parts(ptr, new_size))
+            },
+
+            // SAFETY: because `new_size` must be smaller than or equal to `old_layout.size()`,
+            // both the old and new memory allocation are valid for reads and writes for `new_size`
+            // bytes. Also, because the old allocation wasn't yet deallocated, it cannot overlap
+            // `new_ptr`. Thus, the call to `copy_nonoverlapping` is safe. The safety contract
+            // for `dealloc` must be upheld by the caller.
+            new_size => unsafe {
+                let new_ptr = self.allocate(new_layout)?;
+                ptr::copy_nonoverlapping(ptr.as_ptr(), new_ptr.as_mut_ptr(), new_size);
+                self.deallocate(ptr, old_layout);
+                Ok(new_ptr)
+            },
+        }
+    }
+}
+
+/// The allocator for unique pointers.
+#[cfg(all(not(no_global_oom_handling), not(test)))]
+#[lang = "exchange_malloc"]
+#[inline]
+unsafe fn exchange_malloc(size: usize, align: usize) -> *mut u8 {
+    let layout = unsafe { Layout::from_size_align_unchecked(size, align) };
+    match Global.allocate(layout) {
+        Ok(ptr) => ptr.as_mut_ptr(),
+        Err(_) => handle_alloc_error(layout),
+    }
+}
+
+#[cfg_attr(not(test), lang = "box_free")]
+#[inline]
+#[rustc_const_unstable(feature = "const_box", issue = "92521")]
+// This signature has to be the same as `Box`, otherwise an ICE will happen.
+// When an additional parameter to `Box` is added (like `A: Allocator`), this has to be added here as
+// well.
+// For example if `Box` is changed to  `struct Box<T: ?Sized, A: Allocator>(Unique<T>, A)`,
+// this function has to be changed to `fn box_free<T: ?Sized, A: Allocator>(Unique<T>, A)` as well.
+pub(crate) const unsafe fn box_free<T: ?Sized, A: ~const Allocator + ~const Destruct>(
+    ptr: Unique<T>,
+    alloc: A,
+) {
+    unsafe {
+        let size = size_of_val(ptr.as_ref());
+        let align = min_align_of_val(ptr.as_ref());
+        let layout = Layout::from_size_align_unchecked(size, align);
+        alloc.deallocate(From::from(ptr.cast()), layout)
+    }
+}
+
+// # Allocation error handler
+
+#[cfg(not(no_global_oom_handling))]
+extern "Rust" {
+    // This is the magic symbol to call the global alloc error handler.  rustc generates
+    // it to call `__rg_oom` if there is a `#[alloc_error_handler]`, or to call the
+    // default implementations below (`__rdl_oom`) otherwise.
+    fn __rust_alloc_error_handler(size: usize, align: usize) -> !;
+}
+
+/// Abort on memory allocation error or failure.
+///
+/// Callers of memory allocation APIs wishing to abort computation
+/// in response to an allocation error are encouraged to call this function,
+/// rather than directly invoking `panic!` or similar.
+///
+/// The default behavior of this function is to print a message to standard error
+/// and abort the process.
+/// It can be replaced with [`set_alloc_error_hook`] and [`take_alloc_error_hook`].
+///
+/// [`set_alloc_error_hook`]: ../../std/alloc/fn.set_alloc_error_hook.html
+/// [`take_alloc_error_hook`]: ../../std/alloc/fn.take_alloc_error_hook.html
+#[stable(feature = "global_alloc", since = "1.28.0")]
+#[rustc_const_unstable(feature = "const_alloc_error", issue = "92523")]
+#[cfg(all(not(no_global_oom_handling), not(test)))]
+#[cold]
+pub const fn handle_alloc_error(layout: Layout) -> ! {
+    const fn ct_error(_: Layout) -> ! {
+        panic!("allocation failed");
+    }
+
+    fn rt_error(layout: Layout) -> ! {
+        unsafe {
+            __rust_alloc_error_handler(layout.size(), layout.align());
+        }
+    }
+
+    unsafe { core::intrinsics::const_eval_select((layout,), ct_error, rt_error) }
+}
+
+// For alloc test `std::alloc::handle_alloc_error` can be used directly.
+#[cfg(all(not(no_global_oom_handling), test))]
+pub use std::alloc::handle_alloc_error;
+
+#[cfg(all(not(no_global_oom_handling), not(test)))]
+#[doc(hidden)]
+#[allow(unused_attributes)]
+#[unstable(feature = "alloc_internals", issue = "none")]
+pub mod __alloc_error_handler {
+    use crate::alloc::Layout;
+
+    // called via generated `__rust_alloc_error_handler`
+
+    // if there is no `#[alloc_error_handler]`
+    #[rustc_std_internal_symbol]
+    pub unsafe extern "C-unwind" fn __rdl_oom(size: usize, _align: usize) -> ! {
+        panic!("memory allocation of {size} bytes failed")
+    }
+
+    // if there is an `#[alloc_error_handler]`
+    #[rustc_std_internal_symbol]
+    pub unsafe extern "C-unwind" fn __rg_oom(size: usize, align: usize) -> ! {
+        let layout = unsafe { Layout::from_size_align_unchecked(size, align) };
+        extern "Rust" {
+            #[lang = "oom"]
+            fn oom_impl(layout: Layout) -> !;
+        }
+        unsafe { oom_impl(layout) }
+    }
+}
+
+/// Specialize clones into pre-allocated, uninitialized memory.
+/// Used by `Box::clone` and `Rc`/`Arc::make_mut`.
+pub(crate) trait WriteCloneIntoRaw: Sized {
+    unsafe fn write_clone_into_raw(&self, target: *mut Self);
+}
+
+impl<T: Clone> WriteCloneIntoRaw for T {
+    #[inline]
+    default unsafe fn write_clone_into_raw(&self, target: *mut Self) {
+        // Having allocated *first* may allow the optimizer to create
+        // the cloned value in-place, skipping the local and move.
+        unsafe { target.write(self.clone()) };
+    }
+}
+
+impl<T: Copy> WriteCloneIntoRaw for T {
+    #[inline]
+    unsafe fn write_clone_into_raw(&self, target: *mut Self) {
+        // We can always copy in-place, without ever involving a local value.
+        unsafe { target.copy_from_nonoverlapping(self, 1) };
+    }
+}

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index 6162b5c6d4c9..ca224a541770 100644
@@ -1,3 +1,5 @@
+// SPDX-License-Identifier: Apache-2.0 OR MIT
+
 //! Memory allocation APIs
 
 #![stable(feature = "alloc_module", since = "1.28.0")]

index cb4e438f8bea..dde4957200d4 100644
@@ -1,3 +1,5 @@
+// SPDX-License-Identifier: Apache-2.0 OR MIT
+
 //! A module for working with borrowed data.
 
 #![stable(feature = "rust1", since = "1.0.0")]

@@ -11,7 +13,7 @@ use core::ops::{Add, AddAssign};
 #[stable(feature = "rust1", since = "1.0.0")]
 pub use core::borrow::{Borrow, BorrowMut};
 
-use crate::fmt;
+use core::fmt;
 #[cfg(not(no_global_oom_handling))]
 use crate::string::String;
 

index c07536f0d0ce..dcfe87b14f3a 100644
@@ -1,3 +1,5 @@
+// SPDX-License-Identifier: Apache-2.0 OR MIT
+
 //! A pointer type for heap allocation.
 //!
 //! [`Box<T>`], casually referred to as a 'box', provides the simplest form of

@@ -163,9 +165,11 @@ use crate::str::from_boxed_utf8_unchecked;
 #[cfg(not(no_global_oom_handling))]
 use crate::vec::Vec;
 
+#[cfg(not(no_thin))]
 #[unstable(feature = "thin_box", issue = "92791")]
 pub use thin::ThinBox;
 
+#[cfg(not(no_thin))]
 mod thin;
 
 /// A pointer type for heap allocation.

index 628a5b155673..1eec265b28f8 100644
@@ -1,3 +1,5 @@
+// SPDX-License-Identifier: Apache-2.0 OR MIT
+
 //! Collection types.
 
 #![stable(feature = "rust1", since = "1.0.0")]

index fd21b3671182..233bcd5e4654 100644
@@ -1,3 +1,5 @@
+// SPDX-License-Identifier: Apache-2.0 OR MIT
+
 //! # The Rust core allocation and collections library
 //!
 //! This library provides smart pointers and collections for managing

@@ -192,6 +194,7 @@ extern crate std;
 extern crate test;
 
 // Module with internal macros used by other modules (needs to be included before other modules).
+#[cfg(not(no_macros))]
 #[macro_use]
 mod macros;
 

@@ -216,11 +219,16 @@ pub mod borrow;
 pub mod collections;
 #[cfg(not(no_global_oom_handling))]
 pub mod ffi;
+#[cfg(not(no_fmt))]
 pub mod fmt;
+#[cfg(not(no_rc))]
 pub mod rc;
 pub mod slice;
+#[cfg(not(no_str))]
 pub mod str;
+#[cfg(not(no_string))]
 pub mod string;
+#[cfg(not(no_sync))]
 #[cfg(target_has_atomic = "ptr")]
 pub mod sync;
 #[cfg(all(not(no_global_oom_handling), target_has_atomic = "ptr"))]

index 4be5f6cf9ca5..daf5f2da7168 100644
@@ -1,3 +1,5 @@
+// SPDX-License-Identifier: Apache-2.0 OR MIT
+
 #![unstable(feature = "raw_vec_internals", reason = "unstable const warnings", issue = "none")]
 
 use core::alloc::LayoutError;

@@ -307,6 +309,12 @@ impl<T, A: Allocator> RawVec<T, A> {
         }
     }
 
+    /// The same as `reserve_for_push`, but returns on errors instead of panicking or aborting.
+    #[inline(never)]
+    pub fn try_reserve_for_push(&mut self, len: usize) -> Result<(), TryReserveError> {
+        self.grow_amortized(len, 1)
+    }
+
     /// Ensures that the buffer contains at least enough space to hold `len +
     /// additional` elements. If it doesn't already, will reallocate the
     /// minimum possible amount of memory necessary. Generally this will be

@@ -421,6 +429,7 @@ impl<T, A: Allocator> RawVec<T, A> {
         Ok(())
     }
 
+    #[allow(dead_code)]
     fn shrink(&mut self, cap: usize) -> Result<(), TryReserveError> {
         assert!(cap <= self.capacity(), "Tried to shrink to a larger capacity");
 

index 199b3c9d0290..e444e97fa145 100644
@@ -1,3 +1,5 @@
+// SPDX-License-Identifier: Apache-2.0 OR MIT
+
 //! A dynamically-sized view into a contiguous sequence, `[T]`.
 //!
 //! *[See also the slice primitive type](slice).*

index 5cdee0bd4da4..b6a5f98e4fcd 100644
@@ -1,3 +1,5 @@
+// SPDX-License-Identifier: Apache-2.0 OR MIT
+
 use crate::alloc::{Allocator, Global};
 use core::fmt;
 use core::iter::{FusedIterator, TrustedLen};

index 3c37c92ae44b..b04fce041622 100644
@@ -1,3 +1,5 @@
+// SPDX-License-Identifier: Apache-2.0 OR MIT
+
 use crate::alloc::{Allocator, Global};
 use core::ptr::{self};
 use core::slice::{self};

index 9b84a1d9b4b6..f7a50e76691e 100644
@@ -1,3 +1,5 @@
+// SPDX-License-Identifier: Apache-2.0 OR MIT
+
 #[cfg(not(no_global_oom_handling))]
 use super::AsVecIntoIter;
 use crate::alloc::{Allocator, Global};

@@ -9,6 +11,7 @@ use core::iter::{
 };
 use core::marker::PhantomData;
 use core::mem::{self, ManuallyDrop};
+#[cfg(not(no_global_oom_handling))]
 use core::ops::Deref;
 use core::ptr::{self, NonNull};
 use core::slice::{self};

@@ -123,6 +126,7 @@ impl<T, A: Allocator> IntoIter<T, A> {
     }
 
     /// Forgets to Drop the remaining elements while still allowing the backing allocation to be freed.
+    #[allow(dead_code)]
     pub(crate) fn forget_remaining_elements(&mut self) {
         self.ptr = self.end;
     }

index edf270db81d4..377f3d172777 100644
@@ -1,3 +1,5 @@
+// SPDX-License-Identifier: Apache-2.0 OR MIT
+
 use crate::boxed::Box;
 
 #[rustc_specialization_trait]

index 3dc8a4fbba86..540787804cc2 100644
@@ -1,3 +1,5 @@
+// SPDX-License-Identifier: Apache-2.0 OR MIT
+
 //! A contiguous growable array type with heap-allocated contents, written
 //! `Vec<T>`.
 //!

@@ -1739,6 +1741,29 @@ impl<T, A: Allocator> Vec<T, A> {
         }
     }
 
+    /// Tries to append an element to the back of a collection.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let mut vec = vec![1, 2];
+    /// vec.try_push(3).unwrap();
+    /// assert_eq!(vec, [1, 2, 3]);
+    /// ```
+    #[inline]
+    #[stable(feature = "kernel", since = "1.0.0")]
+    pub fn try_push(&mut self, value: T) -> Result<(), TryReserveError> {
+        if self.len == self.buf.capacity() {
+            self.buf.try_reserve_for_push(self.len)?;
+        }
+        unsafe {
+            let end = self.as_mut_ptr().add(self.len);
+            ptr::write(end, value);
+            self.len += 1;
+        }
+        Ok(())
+    }
+
     /// Removes the last element from a vector and returns it, or [`None`] if it
     /// is empty.
     ///

index b0cf72577a1b..10ad4e492287 100644
@@ -1,3 +1,5 @@
+// SPDX-License-Identifier: Apache-2.0 OR MIT
+
 use crate::alloc::Allocator;
 #[cfg(not(no_global_oom_handling))]
 use crate::borrow::Cow;

new file mode 100644
index 000000000000..f8f39a3e6855
@@ -0,0 +1,63 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Our own `compiler_builtins`.
+//!
+//! Rust provides [`compiler_builtins`] as a port of LLVM's [`compiler-rt`].
+//! Since we do not need the vast majority of them, we avoid the dependency
+//! by providing this file.
+//!
+//! At the moment, some builtins are required that should not be. For instance,
+//! [`core`] has 128-bit integers functionality which we should not be compiling
+//! in. We will work with upstream [`core`] to provide feature flags to disable
+//! the parts we do not need. For the moment, we define them to [`panic!`] at
+//! runtime for simplicity to catch mistakes, instead of performing surgery
+//! on `core.o`.
+//!
+//! In any case, all these symbols are weakened to ensure we do not override
+//! those that may be provided by the rest of the kernel.
+//!
+//! [`compiler_builtins`]: https://github.com/rust-lang/compiler-builtins
+//! [`compiler-rt`]: https://compiler-rt.llvm.org/
+
+#![feature(compiler_builtins)]
+#![compiler_builtins]
+#![no_builtins]
+#![no_std]
+
+macro_rules! define_panicking_intrinsics(
+    ($reason: tt, { $($ident: ident, )* }) => {
+        $(
+            #[doc(hidden)]
+            #[no_mangle]
+            pub extern "C" fn $ident() {
+                panic!($reason);
+            }
+        )*
+    }
+);
+
+define_panicking_intrinsics!("`f32` should not be used", {
+    __eqsf2,
+    __gesf2,
+    __lesf2,
+    __nesf2,
+    __unordsf2,
+});
+
+define_panicking_intrinsics!("`f64` should not be used", {
+    __unorddf2,
+});
+
+define_panicking_intrinsics!("`i128` should not be used", {
+    __ashrti3,
+    __muloti4,
+    __multi3,
+});
+
+define_panicking_intrinsics!("`u128` should not be used", {
+    __ashlti3,
+    __lshrti3,
+    __udivmodti4,
+    __udivti3,
+    __umodti3,
+});

new file mode 100644
index 000000000000..cdc7dc6135d2
@@ -0,0 +1,51 @@
+// SPDX-License-Identifier: GPL-2.0
+
+use proc_macro::{token_stream, TokenTree};
+
+pub(crate) fn try_ident(it: &mut token_stream::IntoIter) -> Option<String> {
+    if let Some(TokenTree::Ident(ident)) = it.next() {
+        Some(ident.to_string())
+    } else {
+        None
+    }
+}
+
+pub(crate) fn try_literal(it: &mut token_stream::IntoIter) -> Option<String> {
+    if let Some(TokenTree::Literal(literal)) = it.next() {
+        Some(literal.to_string())
+    } else {
+        None
+    }
+}
+
+pub(crate) fn try_byte_string(it: &mut token_stream::IntoIter) -> Option<String> {
+    try_literal(it).and_then(|byte_string| {
+        if byte_string.starts_with("b\"") && byte_string.ends_with('\"') {
+            Some(byte_string[2..byte_string.len() - 1].to_string())
+        } else {
+            None
+        }
+    })
+}
+
+pub(crate) fn expect_ident(it: &mut token_stream::IntoIter) -> String {
+    try_ident(it).expect("Expected Ident")
+}
+
+pub(crate) fn expect_punct(it: &mut token_stream::IntoIter) -> char {
+    if let TokenTree::Punct(punct) = it.next().expect("Reached end of token stream for Punct") {
+        punct.as_char()
+    } else {
+        panic!("Expected Punct");
+    }
+}
+
+pub(crate) fn expect_byte_string(it: &mut token_stream::IntoIter) -> String {
+    try_byte_string(it).expect("Expected byte string")
+}
+
+pub(crate) fn expect_end(it: &mut token_stream::IntoIter) {
+    if it.next().is_some() {
+        panic!("Expected end");
+    }
+}

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new file mode 100644
index 000000000000..c48bc284214a
@@ -0,0 +1,13 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Header that contains the code (mostly headers) for which Rust bindings
+ * will be automatically generated by `bindgen`.
+ *
+ * Sorted alphabetically.
+ */
+
+#include <linux/slab.h>
+
+/* `bindgen` gets confused at certain things. */
+const gfp_t BINDINGS_GFP_KERNEL = GFP_KERNEL;
+const gfp_t BINDINGS___GFP_ZERO = __GFP_ZERO;

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new file mode 100644
index 000000000000..397a3dd57a9b
@@ -0,0 +1,64 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Allocator support.
+
+use core::alloc::{GlobalAlloc, Layout};
+use core::ptr;
+
+use crate::bindings;
+
+struct KernelAllocator;
+
+unsafe impl GlobalAlloc for KernelAllocator {
+    unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
+        // `krealloc()` is used instead of `kmalloc()` because the latter is
+        // an inline function and cannot be bound to as a result.
+        unsafe { bindings::krealloc(ptr::null(), layout.size(), bindings::GFP_KERNEL) as *mut u8 }
+    }
+
+    unsafe fn dealloc(&self, ptr: *mut u8, _layout: Layout) {
+        unsafe {
+            bindings::kfree(ptr as *const core::ffi::c_void);
+        }
+    }
+}
+
+#[global_allocator]
+static ALLOCATOR: KernelAllocator = KernelAllocator;
+
+// `rustc` only generates these for some crate types. Even then, we would need
+// to extract the object file that has them from the archive. For the moment,
+// let's generate them ourselves instead.
+//
+// Note that `#[no_mangle]` implies exported too, nowadays.
+#[no_mangle]
+fn __rust_alloc(size: usize, _align: usize) -> *mut u8 {
+    unsafe { bindings::krealloc(core::ptr::null(), size, bindings::GFP_KERNEL) as *mut u8 }
+}
+
+#[no_mangle]
+fn __rust_dealloc(ptr: *mut u8, _size: usize, _align: usize) {
+    unsafe { bindings::kfree(ptr as *const core::ffi::c_void) };
+}
+
+#[no_mangle]
+fn __rust_realloc(ptr: *mut u8, _old_size: usize, _align: usize, new_size: usize) -> *mut u8 {
+    unsafe {
+        bindings::krealloc(
+            ptr as *const core::ffi::c_void,
+            new_size,
+            bindings::GFP_KERNEL,
+        ) as *mut u8
+    }
+}
+
+#[no_mangle]
+fn __rust_alloc_zeroed(size: usize, _align: usize) -> *mut u8 {
+    unsafe {
+        bindings::krealloc(
+            core::ptr::null(),
+            size,
+            bindings::GFP_KERNEL | bindings::__GFP_ZERO,
+        ) as *mut u8
+    }
+}

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new file mode 100644
index 000000000000..495e22250726
@@ -0,0 +1,20 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! The `kernel` prelude.
+//!
+//! These are the most common items used by Rust code in the kernel,
+//! intended to be imported by all Rust code, for convenience.
+//!
+//! # Examples
+//!
+//! ```
+//! use kernel::prelude::*;
+//! ```
+
+pub use super::{
+    error::{Error, Result},
+    pr_emerg, pr_info, ThisModule,
+};
+pub use alloc::{boxed::Box, vec::Vec};
+pub use core::pin::Pin;
+pub use macros::module;

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index 90fbe4a3f9c8..c88c932dba5b 100644
@@ -224,7 +224,6 @@ THUMB(	fpreg	.req	r7	)
 /*
  * Increment/decrement the preempt count.
  */
-#ifdef CONFIG_PREEMPT_COUNT
 	.macro	inc_preempt_count, ti, tmp
 	ldr	\tmp, [\ti, #TI_PREEMPT]	@ get preempt count
 	add	\tmp, \tmp, #1			@ increment it

@@ -241,16 +240,6 @@ THUMB(	fpreg	.req	r7	)
 	get_thread_info \ti
 	dec_preempt_count \ti, \tmp
 	.endm
-#else
-	.macro	inc_preempt_count, ti, tmp
-	.endm
-
-	.macro	dec_preempt_count, ti, tmp
-	.endm
-
-	.macro	dec_preempt_count_ti, ti, tmp
-	.endm
-#endif
 
 #define USERL(l, x...)				\
 9999:	x;					\

index c10d68cdc3ca..93686bdb9707 100644
@@ -293,8 +293,7 @@ wait_remaining_ms_from_jiffies(unsigned long timestamp_jiffies, int to_wait_ms)
 						   (Wmax))
 #define wait_for(COND, MS)		_wait_for((COND), (MS) * 1000, 10, 1000)
 
-/* If CONFIG_PREEMPT_COUNT is disabled, in_atomic() always reports false. */
-#if defined(CONFIG_DRM_I915_DEBUG) && defined(CONFIG_PREEMPT_COUNT)
+#if defined(CONFIG_DRM_I915_DEBUG)
 # define _WAIT_FOR_ATOMIC_CHECK(ATOMIC) WARN_ON_ONCE((ATOMIC) && !in_atomic())
 #else
 # define _WAIT_FOR_ATOMIC_CHECK(ATOMIC) do { } while (0)

index bbc4730a6505..1e03d54b0b6f 100644
@@ -90,10 +90,8 @@ static inline int bit_spin_is_locked(int bitnum, unsigned long *addr)
 {
 #if defined(CONFIG_SMP) || defined(CONFIG_DEBUG_SPINLOCK)
 	return test_bit(bitnum, addr);
-#elif defined CONFIG_PREEMPT_COUNT
-	return preempt_count();
 #else
-	return 1;
+	return preempt_count();
 #endif
 }
 

index 1f1099dac3f0..a05e40dccb0a 100644
@@ -600,16 +600,14 @@ do {									\
 
 #define lockdep_assert_preemption_enabled()				\
 do {									\
-	WARN_ON_ONCE(IS_ENABLED(CONFIG_PREEMPT_COUNT)	&&		\
-		     __lockdep_enabled			&&		\
+	WARN_ON_ONCE(__lockdep_enabled			&&		\
 		     (preempt_count() != 0		||		\
 		      !this_cpu_read(hardirqs_enabled)));		\
 } while (0)
 
 #define lockdep_assert_preemption_disabled()				\
 do {									\
-	WARN_ON_ONCE(IS_ENABLED(CONFIG_PREEMPT_COUNT)	&&		\
-		     __lockdep_enabled			&&		\
+	WARN_ON_ONCE(__lockdep_enabled			&&		\
 		     (preempt_count() == 0		&&		\
 		      this_cpu_read(hardirqs_enabled)));		\
 } while (0)

index 2e677e6ad09f..4cddcb17489a 100644
@@ -271,9 +271,7 @@ static inline bool folio_ref_try_add_rcu(struct folio *folio, int count)
 	 * context, so (on !SMP) we only need preemption to be disabled
 	 * and TINY_RCU does that for us.
 	 */
-# ifdef CONFIG_PREEMPT_COUNT
 	VM_BUG_ON(!in_atomic() && !irqs_disabled());
-# endif
 	VM_BUG_ON_FOLIO(folio_ref_count(folio) == 0, folio);
 	folio_ref_add(folio, count);
 #else

index b4381f255a5c..77da73007375 100644
@@ -56,8 +56,7 @@
 #define PREEMPT_DISABLED	(PREEMPT_DISABLE_OFFSET + PREEMPT_ENABLED)
 
 /*
- * Disable preemption until the scheduler is running -- use an unconditional
- * value so that it also works on !PREEMPT_COUNT kernels.
+ * Disable preemption until the scheduler is running.
  *
  * Reset by start_kernel()->sched_init()->init_idle()->init_idle_preempt_count().
  */

@@ -69,7 +68,6 @@
  *
  *    preempt_count() == 2*PREEMPT_DISABLE_OFFSET
  *
- * Note: PREEMPT_DISABLE_OFFSET is 0 for !PREEMPT_COUNT kernels.
  * Note: See finish_task_switch().
  */
 #define FORK_PREEMPT_COUNT	(2*PREEMPT_DISABLE_OFFSET + PREEMPT_ENABLED)

@@ -133,11 +131,7 @@ static __always_inline unsigned char interrupt_context_level(void)
 /*
  * The preempt_count offset after preempt_disable();
  */
-#if defined(CONFIG_PREEMPT_COUNT)
-# define PREEMPT_DISABLE_OFFSET	PREEMPT_OFFSET
-#else
-# define PREEMPT_DISABLE_OFFSET	0
-#endif
+#define PREEMPT_DISABLE_OFFSET	PREEMPT_OFFSET
 
 /*
  * The preempt_count offset after spin_lock()

@@ -154,7 +148,7 @@ static __always_inline unsigned char interrupt_context_level(void)
  *
  *  spin_lock_bh()
  *
- * Which need to disable both preemption (CONFIG_PREEMPT_COUNT) and
+ * Which need to disable both preemption and
  * softirqs, such that unlock sequences of:
  *
  *  spin_unlock();

@@ -196,8 +190,6 @@ extern void preempt_count_sub(int val);
 #define preempt_count_inc() preempt_count_add(1)
 #define preempt_count_dec() preempt_count_sub(1)
 
-#ifdef CONFIG_PREEMPT_COUNT
-
 #define preempt_disable() \
 do { \
 	preempt_count_inc(); \

@@ -263,27 +255,6 @@ do { \
 	__preempt_count_dec(); \
 } while (0)
 
-#else /* !CONFIG_PREEMPT_COUNT */
-
-/*
- * Even if we don't have any preemption, we need preempt disable/enable
- * to be barriers, so that we don't have things like get_user/put_user
- * that can cause faults and scheduling migrate into our preempt-protected
- * region.
- */
-#define preempt_disable()			barrier()
-#define sched_preempt_enable_no_resched()	barrier()
-#define preempt_enable_no_resched()		barrier()
-#define preempt_enable()			barrier()
-#define preempt_check_resched()			do { } while (0)
-
-#define preempt_disable_notrace()		barrier()
-#define preempt_enable_no_resched_notrace()	barrier()
-#define preempt_enable_notrace()		barrier()
-#define preemptible()				0
-
-#endif /* CONFIG_PREEMPT_COUNT */
-
 #ifdef MODULE
 /*
  * Modules have no business playing preemption tricks.

index 47e5d374c7eb..8761b85c7874 100644
@@ -225,9 +225,6 @@ static inline bool pagefault_disabled(void)
  *
  * This function should only be used by the fault handlers. Other users should
  * stick to pagefault_disabled().
- * Please NEVER use preempt_disable() to disable the fault handler. With
- * !CONFIG_PREEMPT_COUNT, this is like a NOP. So the handler won't be disabled.
- * in_atomic() will report different values based on !CONFIG_PREEMPT_COUNT.
  */
 #define faulthandler_disabled() (pagefault_disabled() || in_atomic())
 

index 79aea7df4345..c21a83e7b534 100644
@@ -2478,7 +2478,7 @@ static __latent_entropy void rcu_core(void)
 	WARN_ON_ONCE(!rdp->beenonline);
 
 	/* Report any deferred quiescent states if preemption enabled. */
-	if (IS_ENABLED(CONFIG_PREEMPT_COUNT) && (!(preempt_count() & PREEMPT_MASK))) {
+	if (!(preempt_count() & PREEMPT_MASK)) {
 		rcu_preempt_deferred_qs(current);
 	} else if (rcu_preempt_need_deferred_qs(current)) {
 		set_tsk_need_resched(current);

index 438ecae6bd7e..432aa6e6cff7 100644
@@ -29,7 +29,7 @@ static bool rcu_rdp_is_offloaded(struct rcu_data *rdp)
 		  (IS_ENABLED(CONFIG_HOTPLUG_CPU) && lockdep_is_cpus_held()) ||
 		  rcu_lockdep_is_held_nocb(rdp) ||
 		  (rdp == this_cpu_ptr(&rcu_data) &&
-		   !(IS_ENABLED(CONFIG_PREEMPT_COUNT) && preemptible())) ||
+		   !preemptible()) ||
 		  rcu_current_is_nocb_kthread(rdp)),
 		"Unsafe read of RCU_NOCB offloaded state"
 	);

index ee28253c9ac0..938f41569ae9 100644
@@ -5111,8 +5111,7 @@ asmlinkage __visible void schedule_tail(struct task_struct *prev)
 	 * finish_task_switch() for details.
 	 *
 	 * finish_task_switch() will drop rq->lock() and lower preempt_count
-	 * and the preempt_enable() will end up enabling preemption (on
-	 * PREEMPT_COUNT kernels).
+	 * and the preempt_enable() will end up enabling preemption.
 	 */
 
 	finish_task_switch(prev);

@@ -9901,9 +9900,6 @@ void __cant_sleep(const char *file, int line, int preempt_offset)
 	if (irqs_disabled())
 		return;
 
-	if (!IS_ENABLED(CONFIG_PREEMPT_COUNT))
-		return;
-
 	if (preempt_count() > preempt_offset)
 		return;
 

@@ -9933,9 +9929,6 @@ void __cant_migrate(const char *file, int line)
 	if (is_migration_disabled(current))
 		return;
 
-	if (!IS_ENABLED(CONFIG_PREEMPT_COUNT))
-		return;
-
 	if (preempt_count() > 0)
 		return;
 

index 862dbd9af4f5..b01767226476 100644
@@ -3106,19 +3106,15 @@ static void *__slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node,
 {
 	void *p;
 
-#ifdef CONFIG_PREEMPT_COUNT
 	/*
 	 * We may have been preempted and rescheduled on a different
 	 * cpu before disabling preemption. Need to reload cpu area
 	 * pointer.
 	 */
 	c = slub_get_cpu_ptr(s->cpu_slab);
-#endif
-
 	p = ___slab_alloc(s, gfpflags, node, addr, c);
-#ifdef CONFIG_PREEMPT_COUNT
 	slub_put_cpu_ptr(s->cpu_slab);
-#endif
+
 	return p;
 }
 

index 283d7103334f..d0d485d48649 100644
@@ -8,7 +8,6 @@
 #undef CONFIG_HOTPLUG_CPU
 #undef CONFIG_MODULES
 #undef CONFIG_NO_HZ_FULL_SYSIDLE
-#undef CONFIG_PREEMPT_COUNT
 #undef CONFIG_PREEMPT_RCU
 #undef CONFIG_PROVE_RCU
 #undef CONFIG_RCU_NOCB_CPU