1 // SPDX-License-Identifier: GPL-2.0 2 3 //! Kernel page allocation and management. 4 5 use crate::{ 6 alloc::{AllocError, Flags}, 7 bindings, 8 error::code::*, 9 error::Result, 10 uaccess::UserSliceReader, 11 }; 12 use core::ptr::{self, NonNull}; 13 14 /// A bitwise shift for the page size. 15 pub const PAGE_SHIFT: usize = bindings::PAGE_SHIFT as usize; 16 17 /// The number of bytes in a page. 18 pub const PAGE_SIZE: usize = bindings::PAGE_SIZE; 19 20 /// A bitmask that gives the page containing a given address. 21 pub const PAGE_MASK: usize = !(PAGE_SIZE - 1); 22 23 /// Round up the given number to the next multiple of [`PAGE_SIZE`]. 24 /// 25 /// It is incorrect to pass an address where the next multiple of [`PAGE_SIZE`] doesn't fit in a 26 /// [`usize`]. 27 pub const fn page_align(addr: usize) -> usize { 28 // Parentheses around `PAGE_SIZE - 1` to avoid triggering overflow sanitizers in the wrong 29 // cases. 30 (addr + (PAGE_SIZE - 1)) & PAGE_MASK 31 } 32 33 /// A pointer to a page that owns the page allocation. 34 /// 35 /// # Invariants 36 /// 37 /// The pointer is valid, and has ownership over the page. 38 pub struct Page { 39 page: NonNull<bindings::page>, 40 } 41 42 // SAFETY: Pages have no logic that relies on them staying on a given thread, so moving them across 43 // threads is safe. 44 unsafe impl Send for Page {} 45 46 // SAFETY: Pages have no logic that relies on them not being accessed concurrently, so accessing 47 // them concurrently is safe. 48 unsafe impl Sync for Page {} 49 50 impl Page { 51 /// Allocates a new page. 52 /// 53 /// # Examples 54 /// 55 /// Allocate memory for a page. 56 /// 57 /// ``` 58 /// use kernel::page::Page; 59 /// 60 /// let page = Page::alloc_page(GFP_KERNEL)?; 61 /// # Ok::<(), kernel::alloc::AllocError>(()) 62 /// ``` 63 /// 64 /// Allocate memory for a page and zero its contents. 65 /// 66 /// ``` 67 /// use kernel::page::Page; 68 /// 69 /// let page = Page::alloc_page(GFP_KERNEL | __GFP_ZERO)?; 70 /// # Ok::<(), kernel::alloc::AllocError>(()) 71 /// ``` 72 #[inline] 73 pub fn alloc_page(flags: Flags) -> Result<Self, AllocError> { 74 // SAFETY: Depending on the value of `gfp_flags`, this call may sleep. Other than that, it 75 // is always safe to call this method. 76 let page = unsafe { bindings::alloc_pages(flags.as_raw(), 0) }; 77 let page = NonNull::new(page).ok_or(AllocError)?; 78 // INVARIANT: We just successfully allocated a page, so we now have ownership of the newly 79 // allocated page. We transfer that ownership to the new `Page` object. 80 Ok(Self { page }) 81 } 82 83 /// Returns a raw pointer to the page. 84 pub fn as_ptr(&self) -> *mut bindings::page { 85 self.page.as_ptr() 86 } 87 88 /// Runs a piece of code with this page mapped to an address. 89 /// 90 /// The page is unmapped when this call returns. 91 /// 92 /// # Using the raw pointer 93 /// 94 /// It is up to the caller to use the provided raw pointer correctly. The pointer is valid for 95 /// `PAGE_SIZE` bytes and for the duration in which the closure is called. The pointer might 96 /// only be mapped on the current thread, and when that is the case, dereferencing it on other 97 /// threads is UB. Other than that, the usual rules for dereferencing a raw pointer apply: don't 98 /// cause data races, the memory may be uninitialized, and so on. 99 /// 100 /// If multiple threads map the same page at the same time, then they may reference with 101 /// different addresses. However, even if the addresses are different, the underlying memory is 102 /// still the same for these purposes (e.g., it's still a data race if they both write to the 103 /// same underlying byte at the same time). 104 fn with_page_mapped<T>(&self, f: impl FnOnce(*mut u8) -> T) -> T { 105 // SAFETY: `page` is valid due to the type invariants on `Page`. 106 let mapped_addr = unsafe { bindings::kmap_local_page(self.as_ptr()) }; 107 108 let res = f(mapped_addr.cast()); 109 110 // This unmaps the page mapped above. 111 // 112 // SAFETY: Since this API takes the user code as a closure, it can only be used in a manner 113 // where the pages are unmapped in reverse order. This is as required by `kunmap_local`. 114 // 115 // In other words, if this call to `kunmap_local` happens when a different page should be 116 // unmapped first, then there must necessarily be a call to `kmap_local_page` other than the 117 // call just above in `with_page_mapped` that made that possible. In this case, it is the 118 // unsafe block that wraps that other call that is incorrect. 119 unsafe { bindings::kunmap_local(mapped_addr) }; 120 121 res 122 } 123 124 /// Runs a piece of code with a raw pointer to a slice of this page, with bounds checking. 125 /// 126 /// If `f` is called, then it will be called with a pointer that points at `off` bytes into the 127 /// page, and the pointer will be valid for at least `len` bytes. The pointer is only valid on 128 /// this task, as this method uses a local mapping. 129 /// 130 /// If `off` and `len` refers to a region outside of this page, then this method returns 131 /// [`EINVAL`] and does not call `f`. 132 /// 133 /// # Using the raw pointer 134 /// 135 /// It is up to the caller to use the provided raw pointer correctly. The pointer is valid for 136 /// `len` bytes and for the duration in which the closure is called. The pointer might only be 137 /// mapped on the current thread, and when that is the case, dereferencing it on other threads 138 /// is UB. Other than that, the usual rules for dereferencing a raw pointer apply: don't cause 139 /// data races, the memory may be uninitialized, and so on. 140 /// 141 /// If multiple threads map the same page at the same time, then they may reference with 142 /// different addresses. However, even if the addresses are different, the underlying memory is 143 /// still the same for these purposes (e.g., it's still a data race if they both write to the 144 /// same underlying byte at the same time). 145 fn with_pointer_into_page<T>( 146 &self, 147 off: usize, 148 len: usize, 149 f: impl FnOnce(*mut u8) -> Result<T>, 150 ) -> Result<T> { 151 let bounds_ok = off <= PAGE_SIZE && len <= PAGE_SIZE && (off + len) <= PAGE_SIZE; 152 153 if bounds_ok { 154 self.with_page_mapped(move |page_addr| { 155 // SAFETY: The `off` integer is at most `PAGE_SIZE`, so this pointer offset will 156 // result in a pointer that is in bounds or one off the end of the page. 157 f(unsafe { page_addr.add(off) }) 158 }) 159 } else { 160 Err(EINVAL) 161 } 162 } 163 164 /// Maps the page and reads from it into the given buffer. 165 /// 166 /// This method will perform bounds checks on the page offset. If `offset .. offset+len` goes 167 /// outside of the page, then this call returns [`EINVAL`]. 168 /// 169 /// # Safety 170 /// 171 /// * Callers must ensure that `dst` is valid for writing `len` bytes. 172 /// * Callers must ensure that this call does not race with a write to the same page that 173 /// overlaps with this read. 174 pub unsafe fn read_raw(&self, dst: *mut u8, offset: usize, len: usize) -> Result { 175 self.with_pointer_into_page(offset, len, move |src| { 176 // SAFETY: If `with_pointer_into_page` calls into this closure, then 177 // it has performed a bounds check and guarantees that `src` is 178 // valid for `len` bytes. 179 // 180 // There caller guarantees that there is no data race. 181 unsafe { ptr::copy_nonoverlapping(src, dst, len) }; 182 Ok(()) 183 }) 184 } 185 186 /// Maps the page and writes into it from the given buffer. 187 /// 188 /// This method will perform bounds checks on the page offset. If `offset .. offset+len` goes 189 /// outside of the page, then this call returns [`EINVAL`]. 190 /// 191 /// # Safety 192 /// 193 /// * Callers must ensure that `src` is valid for reading `len` bytes. 194 /// * Callers must ensure that this call does not race with a read or write to the same page 195 /// that overlaps with this write. 196 pub unsafe fn write_raw(&self, src: *const u8, offset: usize, len: usize) -> Result { 197 self.with_pointer_into_page(offset, len, move |dst| { 198 // SAFETY: If `with_pointer_into_page` calls into this closure, then it has performed a 199 // bounds check and guarantees that `dst` is valid for `len` bytes. 200 // 201 // There caller guarantees that there is no data race. 202 unsafe { ptr::copy_nonoverlapping(src, dst, len) }; 203 Ok(()) 204 }) 205 } 206 207 /// Maps the page and zeroes the given slice. 208 /// 209 /// This method will perform bounds checks on the page offset. If `offset .. offset+len` goes 210 /// outside of the page, then this call returns [`EINVAL`]. 211 /// 212 /// # Safety 213 /// 214 /// Callers must ensure that this call does not race with a read or write to the same page that 215 /// overlaps with this write. 216 pub unsafe fn fill_zero_raw(&self, offset: usize, len: usize) -> Result { 217 self.with_pointer_into_page(offset, len, move |dst| { 218 // SAFETY: If `with_pointer_into_page` calls into this closure, then it has performed a 219 // bounds check and guarantees that `dst` is valid for `len` bytes. 220 // 221 // There caller guarantees that there is no data race. 222 unsafe { ptr::write_bytes(dst, 0u8, len) }; 223 Ok(()) 224 }) 225 } 226 227 /// Copies data from userspace into this page. 228 /// 229 /// This method will perform bounds checks on the page offset. If `offset .. offset+len` goes 230 /// outside of the page, then this call returns [`EINVAL`]. 231 /// 232 /// Like the other `UserSliceReader` methods, data races are allowed on the userspace address. 233 /// However, they are not allowed on the page you are copying into. 234 /// 235 /// # Safety 236 /// 237 /// Callers must ensure that this call does not race with a read or write to the same page that 238 /// overlaps with this write. 239 pub unsafe fn copy_from_user_slice_raw( 240 &self, 241 reader: &mut UserSliceReader, 242 offset: usize, 243 len: usize, 244 ) -> Result { 245 self.with_pointer_into_page(offset, len, move |dst| { 246 // SAFETY: If `with_pointer_into_page` calls into this closure, then it has performed a 247 // bounds check and guarantees that `dst` is valid for `len` bytes. Furthermore, we have 248 // exclusive access to the slice since the caller guarantees that there are no races. 249 reader.read_raw(unsafe { core::slice::from_raw_parts_mut(dst.cast(), len) }) 250 }) 251 } 252 } 253 254 impl Drop for Page { 255 #[inline] 256 fn drop(&mut self) { 257 // SAFETY: By the type invariants, we have ownership of the page and can free it. 258 unsafe { bindings::__free_pages(self.page.as_ptr(), 0) }; 259 } 260 } 261