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 pub fn alloc_page(flags: Flags) -> Result<Self, AllocError> { 73 // SAFETY: Depending on the value of `gfp_flags`, this call may sleep. Other than that, it 74 // is always safe to call this method. 75 let page = unsafe { bindings::alloc_pages(flags.as_raw(), 0) }; 76 let page = NonNull::new(page).ok_or(AllocError)?; 77 // INVARIANT: We just successfully allocated a page, so we now have ownership of the newly 78 // allocated page. We transfer that ownership to the new `Page` object. 79 Ok(Self { page }) 80 } 81 82 /// Returns a raw pointer to the page. 83 pub fn as_ptr(&self) -> *mut bindings::page { 84 self.page.as_ptr() 85 } 86 87 /// Runs a piece of code with this page mapped to an address. 88 /// 89 /// The page is unmapped when this call returns. 90 /// 91 /// # Using the raw pointer 92 /// 93 /// It is up to the caller to use the provided raw pointer correctly. The pointer is valid for 94 /// `PAGE_SIZE` bytes and for the duration in which the closure is called. The pointer might 95 /// only be mapped on the current thread, and when that is the case, dereferencing it on other 96 /// threads is UB. Other than that, the usual rules for dereferencing a raw pointer apply: don't 97 /// cause data races, the memory may be uninitialized, and so on. 98 /// 99 /// If multiple threads map the same page at the same time, then they may reference with 100 /// different addresses. However, even if the addresses are different, the underlying memory is 101 /// still the same for these purposes (e.g., it's still a data race if they both write to the 102 /// same underlying byte at the same time). 103 fn with_page_mapped<T>(&self, f: impl FnOnce(*mut u8) -> T) -> T { 104 // SAFETY: `page` is valid due to the type invariants on `Page`. 105 let mapped_addr = unsafe { bindings::kmap_local_page(self.as_ptr()) }; 106 107 let res = f(mapped_addr.cast()); 108 109 // This unmaps the page mapped above. 110 // 111 // SAFETY: Since this API takes the user code as a closure, it can only be used in a manner 112 // where the pages are unmapped in reverse order. This is as required by `kunmap_local`. 113 // 114 // In other words, if this call to `kunmap_local` happens when a different page should be 115 // unmapped first, then there must necessarily be a call to `kmap_local_page` other than the 116 // call just above in `with_page_mapped` that made that possible. In this case, it is the 117 // unsafe block that wraps that other call that is incorrect. 118 unsafe { bindings::kunmap_local(mapped_addr) }; 119 120 res 121 } 122 123 /// Runs a piece of code with a raw pointer to a slice of this page, with bounds checking. 124 /// 125 /// If `f` is called, then it will be called with a pointer that points at `off` bytes into the 126 /// page, and the pointer will be valid for at least `len` bytes. The pointer is only valid on 127 /// this task, as this method uses a local mapping. 128 /// 129 /// If `off` and `len` refers to a region outside of this page, then this method returns 130 /// [`EINVAL`] and does not call `f`. 131 /// 132 /// # Using the raw pointer 133 /// 134 /// It is up to the caller to use the provided raw pointer correctly. The pointer is valid for 135 /// `len` bytes and for the duration in which the closure is called. The pointer might only be 136 /// mapped on the current thread, and when that is the case, dereferencing it on other threads 137 /// is UB. Other than that, the usual rules for dereferencing a raw pointer apply: don't cause 138 /// data races, the memory may be uninitialized, and so on. 139 /// 140 /// If multiple threads map the same page at the same time, then they may reference with 141 /// different addresses. However, even if the addresses are different, the underlying memory is 142 /// still the same for these purposes (e.g., it's still a data race if they both write to the 143 /// same underlying byte at the same time). 144 fn with_pointer_into_page<T>( 145 &self, 146 off: usize, 147 len: usize, 148 f: impl FnOnce(*mut u8) -> Result<T>, 149 ) -> Result<T> { 150 let bounds_ok = off <= PAGE_SIZE && len <= PAGE_SIZE && (off + len) <= PAGE_SIZE; 151 152 if bounds_ok { 153 self.with_page_mapped(move |page_addr| { 154 // SAFETY: The `off` integer is at most `PAGE_SIZE`, so this pointer offset will 155 // result in a pointer that is in bounds or one off the end of the page. 156 f(unsafe { page_addr.add(off) }) 157 }) 158 } else { 159 Err(EINVAL) 160 } 161 } 162 163 /// Maps the page and reads from it into the given buffer. 164 /// 165 /// This method will perform bounds checks on the page offset. If `offset .. offset+len` goes 166 /// outside of the page, then this call returns [`EINVAL`]. 167 /// 168 /// # Safety 169 /// 170 /// * Callers must ensure that `dst` is valid for writing `len` bytes. 171 /// * Callers must ensure that this call does not race with a write to the same page that 172 /// overlaps with this read. 173 pub unsafe fn read_raw(&self, dst: *mut u8, offset: usize, len: usize) -> Result { 174 self.with_pointer_into_page(offset, len, move |src| { 175 // SAFETY: If `with_pointer_into_page` calls into this closure, then 176 // it has performed a bounds check and guarantees that `src` is 177 // valid for `len` bytes. 178 // 179 // There caller guarantees that there is no data race. 180 unsafe { ptr::copy_nonoverlapping(src, dst, len) }; 181 Ok(()) 182 }) 183 } 184 185 /// Maps the page and writes into it from the given buffer. 186 /// 187 /// This method will perform bounds checks on the page offset. If `offset .. offset+len` goes 188 /// outside of the page, then this call returns [`EINVAL`]. 189 /// 190 /// # Safety 191 /// 192 /// * Callers must ensure that `src` is valid for reading `len` bytes. 193 /// * Callers must ensure that this call does not race with a read or write to the same page 194 /// that overlaps with this write. 195 pub unsafe fn write_raw(&self, src: *const u8, offset: usize, len: usize) -> Result { 196 self.with_pointer_into_page(offset, len, move |dst| { 197 // SAFETY: If `with_pointer_into_page` calls into this closure, then it has performed a 198 // bounds check and guarantees that `dst` is valid for `len` bytes. 199 // 200 // There caller guarantees that there is no data race. 201 unsafe { ptr::copy_nonoverlapping(src, dst, len) }; 202 Ok(()) 203 }) 204 } 205 206 /// Maps the page and zeroes the given slice. 207 /// 208 /// This method will perform bounds checks on the page offset. If `offset .. offset+len` goes 209 /// outside of the page, then this call returns [`EINVAL`]. 210 /// 211 /// # Safety 212 /// 213 /// Callers must ensure that this call does not race with a read or write to the same page that 214 /// overlaps with this write. 215 pub unsafe fn fill_zero_raw(&self, offset: usize, len: usize) -> Result { 216 self.with_pointer_into_page(offset, len, move |dst| { 217 // SAFETY: If `with_pointer_into_page` calls into this closure, then it has performed a 218 // bounds check and guarantees that `dst` is valid for `len` bytes. 219 // 220 // There caller guarantees that there is no data race. 221 unsafe { ptr::write_bytes(dst, 0u8, len) }; 222 Ok(()) 223 }) 224 } 225 226 /// Copies data from userspace into this page. 227 /// 228 /// This method will perform bounds checks on the page offset. If `offset .. offset+len` goes 229 /// outside of the page, then this call returns [`EINVAL`]. 230 /// 231 /// Like the other `UserSliceReader` methods, data races are allowed on the userspace address. 232 /// However, they are not allowed on the page you are copying into. 233 /// 234 /// # Safety 235 /// 236 /// Callers must ensure that this call does not race with a read or write to the same page that 237 /// overlaps with this write. 238 pub unsafe fn copy_from_user_slice_raw( 239 &self, 240 reader: &mut UserSliceReader, 241 offset: usize, 242 len: usize, 243 ) -> Result { 244 self.with_pointer_into_page(offset, len, move |dst| { 245 // SAFETY: If `with_pointer_into_page` calls into this closure, then it has performed a 246 // bounds check and guarantees that `dst` is valid for `len` bytes. Furthermore, we have 247 // exclusive access to the slice since the caller guarantees that there are no races. 248 reader.read_raw(unsafe { core::slice::from_raw_parts_mut(dst.cast(), len) }) 249 }) 250 } 251 } 252 253 impl Drop for Page { 254 fn drop(&mut self) { 255 // SAFETY: By the type invariants, we have ownership of the page and can free it. 256 unsafe { bindings::__free_pages(self.page.as_ptr(), 0) }; 257 } 258 } 259