[PATCH v4 06/13] rust: add `io::{Io, IoRaw}` base types

Danilo Krummrich
2024-12-05T14:16:25Z

I/O memory is typically either mapped through direct calls to ioremap()
or subsystem / bus specific ones such as pci_iomap().

Even though subsystem / bus specific functions to map I/O memory are
based on ioremap() / iounmap() it is not desirable to re-implement them
in Rust.

Instead, implement a base type for I/O mapped memory, which generically
provides the corresponding accessors, such as `Io::readb` or
`Io:try_readb`.

`Io` supports an optional const generic, such that a driver can indicate
the minimal expected and required size of the mapping at compile time.
Correspondingly, calls to the 'non-try' accessors, support compile time
checks of the I/O memory offset to read / write, while the 'try'
accessors, provide boundary checks on runtime.

`IoRaw` is meant to be embedded into a structure (e.g. pci::Bar or
io::IoMem) which creates the actual I/O memory mapping and initializes
`IoRaw` accordingly.

To ensure that I/O mapped memory can't out-live the device it may be
bound to, subsystems must embed the corresponding I/O memory type (e.g.
pci::Bar) into a `Devres` container, such that it gets revoked once the
device is unbound.

Signed-off-by: Danilo Krummrich <dakr@kernel.org>
---
rust/helpers/helpers.c | 1 +
rust/helpers/io.c | 101 ++++++++++++++++
rust/kernel/io.rs | 260 +++++++++++++++++++++++++++++++++++++++++
rust/kernel/lib.rs | 1 +
4 files changed, 363 insertions(+)
create mode 100644 rust/helpers/io.c
create mode 100644 rust/kernel/io.rs

diff --git a/rust/helpers/helpers.c b/rust/helpers/helpers.c
index 060750af6524..63f9b1da179f 100644
--- a/rust/helpers/helpers.c
+++ b/rust/helpers/helpers.c
@@ -14,6 +14,7 @@
#include "cred.c"
#include "err.c"
#include "fs.c"
+#include "io.c"
#include "jump_label.c"
#include "kunit.c"
#include "mutex.c"
diff --git a/rust/helpers/io.c b/rust/helpers/io.c
new file mode 100644
index 000000000000..1dde6374c0e2
--- /dev/null
+++ b/rust/helpers/io.c
@@ -0,0 +1,101 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/io.h>
+
+void __iomem *rust_helper_ioremap(phys_addr_t offset, size_t size)
+{
+ return ioremap(offset, size);
+}
+
+void rust_helper_iounmap(volatile void __iomem *addr)
+{
+ return iounmap(addr);
+}
+
+u8 rust_helper_readb(const volatile void __iomem *addr)
+{
+ return readb(addr);
+}
+
+u16 rust_helper_readw(const volatile void __iomem *addr)
+{
+ return readw(addr);
+}
+
+u32 rust_helper_readl(const volatile void __iomem *addr)
+{
+ return readl(addr);
+}
+
+#ifdef CONFIG_64BIT
+u64 rust_helper_readq(const volatile void __iomem *addr)
+{
+ return readq(addr);
+}
+#endif
+
+void rust_helper_writeb(u8 value, volatile void __iomem *addr)
+{
+ writeb(value, addr);
+}
+
+void rust_helper_writew(u16 value, volatile void __iomem *addr)
+{
+ writew(value, addr);
+}
+
+void rust_helper_writel(u32 value, volatile void __iomem *addr)
+{
+ writel(value, addr);
+}
+
+#ifdef CONFIG_64BIT
+void rust_helper_writeq(u64 value, volatile void __iomem *addr)
+{
+ writeq(value, addr);
+}
+#endif
+
+u8 rust_helper_readb_relaxed(const volatile void __iomem *addr)
+{
+ return readb_relaxed(addr);
+}
+
+u16 rust_helper_readw_relaxed(const volatile void __iomem *addr)
+{
+ return readw_relaxed(addr);
+}
+
+u32 rust_helper_readl_relaxed(const volatile void __iomem *addr)
+{
+ return readl_relaxed(addr);
+}
+
+#ifdef CONFIG_64BIT
+u64 rust_helper_readq_relaxed(const volatile void __iomem *addr)
+{
+ return readq_relaxed(addr);
+}
+#endif
+
+void rust_helper_writeb_relaxed(u8 value, volatile void __iomem *addr)
+{
+ writeb_relaxed(value, addr);
+}
+
+void rust_helper_writew_relaxed(u16 value, volatile void __iomem *addr)
+{
+ writew_relaxed(value, addr);
+}
+
+void rust_helper_writel_relaxed(u32 value, volatile void __iomem *addr)
+{
+ writel_relaxed(value, addr);
+}
+
+#ifdef CONFIG_64BIT
+void rust_helper_writeq_relaxed(u64 value, volatile void __iomem *addr)
+{
+ writeq_relaxed(value, addr);
+}
+#endif
diff --git a/rust/kernel/io.rs b/rust/kernel/io.rs
new file mode 100644
index 000000000000..36aa2ec1bcc8
--- /dev/null
+++ b/rust/kernel/io.rs
@@ -0,0 +1,260 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Memory-mapped IO.
+//!
+//! C header: [`include/asm-generic/io.h`](srctree/include/asm-generic/io.h)
+
+use crate::error::{code::EINVAL, Result};
+use crate::{bindings, build_assert};
+
+/// Raw representation of an MMIO region.
+///
+/// By itself, the existence of an instance of this structure does not provide any guarantees that
+/// the represented MMIO region does exist or is properly mapped.
+///
+/// Instead, the bus specific MMIO implementation must convert this raw representation into an `Io`
+/// instance providing the actual memory accessors. Only by the conversion into an `Io` structure
+/// any guarantees are given.
+pub struct IoRaw<const SIZE: usize = 0> {
+ addr: usize,
+ maxsize: usize,
+}
+
+impl<const SIZE: usize> IoRaw<SIZE> {
+ /// Returns a new `IoRaw` instance on success, an error otherwise.
+ pub fn new(addr: usize, maxsize: usize) -> Result<Self> {
+ if maxsize < SIZE {
+ return Err(EINVAL);
+ }
+
+ Ok(Self { addr, maxsize })
+ }
+
+ /// Returns the base address of the MMIO region.
+ #[inline]
+ pub fn addr(&self) -> usize {
+ self.addr
+ }
+
+ /// Returns the maximum size of the MMIO region.
+ #[inline]
+ pub fn maxsize(&self) -> usize {
+ self.maxsize
+ }
+}
+
+/// IO-mapped memory, starting at the base address @addr and spanning @maxlen bytes.
+///
+/// The creator (usually a subsystem / bus such as PCI) is responsible for creating the
+/// mapping, performing an additional region request etc.
+///
+/// # Invariant
+///
+/// `addr` is the start and `maxsize` the length of valid I/O mapped memory region of size
+/// `maxsize`.
+///
+/// # Examples
+///
+/// ```no_run
+/// # use kernel::{bindings, io::{Io, IoRaw}};
+/// # use core::ops::Deref;
+///
+/// // See also [`pci::Bar`] for a real example.
+/// struct IoMem<const SIZE: usize>(IoRaw<SIZE>);
+///
+/// impl<const SIZE: usize> IoMem<SIZE> {
+/// /// # Safety
+/// ///
+/// /// [`paddr`, `paddr` + `SIZE`) must be a valid MMIO region that is mappable into the CPUs
+/// /// virtual address space.
+/// unsafe fn new(paddr: usize) -> Result<Self>{
+/// // SAFETY: By the safety requirements of this function [`paddr`, `paddr` + `SIZE`) is
+/// // valid for `ioremap`.
+/// let addr = unsafe { bindings::ioremap(paddr as _, SIZE.try_into().unwrap()) };
+/// if addr.is_null() {
+/// return Err(ENOMEM);
+/// }
+///
+/// Ok(IoMem(IoRaw::new(addr as _, SIZE)?))
+/// }
+/// }
+///
+/// impl<const SIZE: usize> Drop for IoMem<SIZE> {
+/// fn drop(&mut self) {
+/// // SAFETY: `self.0.addr()` is guaranteed to be properly mapped by `Self::new`.
+/// unsafe { bindings::iounmap(self.0.addr() as _); };
+/// }
+/// }
+///
+/// impl<const SIZE: usize> Deref for IoMem<SIZE> {
+/// type Target = Io<SIZE>;
+///
+/// fn deref(&self) -> &Self::Target {
+/// // SAFETY: The memory range stored in `self` has been properly mapped in `Self::new`.
+/// unsafe { Io::from_raw(&self.0) }
+/// }
+/// }
+///
+///# fn no_run() -> Result<(), Error> {
+/// // SAFETY: Invalid usage for example purposes.
+/// let iomem = unsafe { IoMem::<{ core::mem::size_of::<u32>() }>::new(0xBAAAAAAD)? };
+/// iomem.writel(0x42, 0x0);
+/// assert!(iomem.try_writel(0x42, 0x0).is_ok());
+/// assert!(iomem.try_writel(0x42, 0x4).is_err());
+/// # Ok(())
+/// # }
+/// ```
+#[repr(transparent)]
+pub struct Io<const SIZE: usize = 0>(IoRaw<SIZE>);
+
+macro_rules! define_read {
+ ($(#[$attr:meta])* $name:ident, $try_name:ident, $type_name:ty) => {
+ /// Read IO data from a given offset known at compile time.
+ ///
+ /// Bound checks are performed on compile time, hence if the offset is not known at compile
+ /// time, the build will fail.
+ $(#[$attr])*
+ #[inline]
+ pub fn $name(&self, offset: usize) -> $type_name {
+ let addr = self.io_addr_assert::<$type_name>(offset);
+
+ // SAFETY: By the type invariant `addr` is a valid address for MMIO operations.
+ unsafe { bindings::$name(addr as _) }
+ }
+
+ /// Read IO data from a given offset.
+ ///
+ /// Bound checks are performed on runtime, it fails if the offset (plus the type size) is
+ /// out of bounds.
+ $(#[$attr])*
+ pub fn $try_name(&self, offset: usize) -> Result<$type_name> {
+ let addr = self.io_addr::<$type_name>(offset)?;
+
+ // SAFETY: By the type invariant `addr` is a valid address for MMIO operations.
+ Ok(unsafe { bindings::$name(addr as _) })
+ }
+ };
+}
+
+macro_rules! define_write {
+ ($(#[$attr:meta])* $name:ident, $try_name:ident, $type_name:ty) => {
+ /// Write IO data from a given offset known at compile time.
+ ///
+ /// Bound checks are performed on compile time, hence if the offset is not known at compile
+ /// time, the build will fail.
+ $(#[$attr])*
+ #[inline]
+ pub fn $name(&self, value: $type_name, offset: usize) {
+ let addr = self.io_addr_assert::<$type_name>(offset);
+
+ // SAFETY: By the type invariant `addr` is a valid address for MMIO operations.
+ unsafe { bindings::$name(value, addr as _, ) }
+ }
+
+ /// Write IO data from a given offset.
+ ///
+ /// Bound checks are performed on runtime, it fails if the offset (plus the type size) is
+ /// out of bounds.
+ $(#[$attr])*
+ pub fn $try_name(&self, value: $type_name, offset: usize) -> Result {
+ let addr = self.io_addr::<$type_name>(offset)?;
+
+ // SAFETY: By the type invariant `addr` is a valid address for MMIO operations.
+ unsafe { bindings::$name(value, addr as _) }
+ Ok(())
+ }
+ };
+}
+
+impl<const SIZE: usize> Io<SIZE> {
+ /// Converts an `IoRaw` into an `Io` instance, providing the accessors to the MMIO mapping.
+ ///
+ /// # Safety
+ ///
+ /// Callers must ensure that `addr` is the start of a valid I/O mapped memory region of size
+ /// `maxsize`.
+ pub unsafe fn from_raw<'a>(raw: &IoRaw<SIZE>) -> &'a Self {
+ // SAFETY: `Io` is a transparent wrapper around `IoRaw`.
+ unsafe { &*core::ptr::from_ref(raw).cast() }
+ }
+
+ /// Returns the base address of this mapping.
+ #[inline]
+ pub fn addr(&self) -> usize {
+ self.0.addr()
+ }
+
+ /// Returns the maximum size of this mapping.
+ #[inline]
+ pub fn maxsize(&self) -> usize {
+ self.0.maxsize()
+ }
+
+ #[inline]
+ const fn offset_valid(offset: usize, size: usize) -> bool {
+ let type_size = core::mem::size_of::();
+ if let Some(end) = offset.checked_add(type_size) {
+ end <= size && offset % type_size == 0
+ } else {
+ false
+ }
+ }
+
+ #[inline]
+ fn io_addr(&self, offset: usize) -> Result<usize> {
+ if !Self::offset_valid::(offset, self.maxsize()) {
+ return Err(EINVAL);
+ }
+
+ // Probably no need to check, since the safety requirements of `Self::new` guarantee that
+ // this can't overflow.
+ self.addr().checked_add(offset).ok_or(EINVAL)
+ }
+
+ #[inline]
+ fn io_addr_assert(&self, offset: usize) -> usize {
+ build_assert!(Self::offset_valid::(offset, SIZE));
+
+ self.addr() + offset
+ }
+
+ define_read!(readb, try_readb, u8);
+ define_read!(readw, try_readw, u16);
+ define_read!(readl, try_readl, u32);
+ define_read!(
+ #[cfg(CONFIG_64BIT)]
+ readq,
+ try_readq,
+ u64
+ );
+
+ define_read!(readb_relaxed, try_readb_relaxed, u8);
+ define_read!(readw_relaxed, try_readw_relaxed, u16);
+ define_read!(readl_relaxed, try_readl_relaxed, u32);
+ define_read!(
+ #[cfg(CONFIG_64BIT)]
+ readq_relaxed,
+ try_readq_relaxed,
+ u64
+ );
+
+ define_write!(writeb, try_writeb, u8);
+ define_write!(writew, try_writew, u16);
+ define_write!(writel, try_writel, u32);
+ define_write!(
+ #[cfg(CONFIG_64BIT)]
+ writeq,
+ try_writeq,
+ u64
+ );
+
+ define_write!(writeb_relaxed, try_writeb_relaxed, u8);
+ define_write!(writew_relaxed, try_writew_relaxed, u16);
+ define_write!(writel_relaxed, try_writel_relaxed, u32);
+ define_write!(
+ #[cfg(CONFIG_64BIT)]
+ writeq_relaxed,
+ try_writeq_relaxed,
+ u64
+ );
+}
diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
index 200c5f99a805..d1f30b1a05fb 100644
--- a/rust/kernel/lib.rs
+++ b/rust/kernel/lib.rs
@@ -79,6 +79,7 @@

#[doc(hidden)]
pub use bindings;
+pub mod io;
pub use macros;
pub use uapi;

--
2.47.0