Re: [PATCH v6 07/16] rust: add `io::{Io, IoRaw}` base types

From: Asahi Lina
Date: Sun Feb 02 2025 - 16:20:23 EST

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On 12/17/24 1:20 AM, Danilo Krummrich wrote:
> On Thu, Dec 12, 2024 at 05:33:38PM +0100, Danilo Krummrich wrote:
>> 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.
>>
>> Reviewed-by: Alice Ryhl <aliceryhl@xxxxxxxxxx>
>> Tested-by: Daniel Almeida <daniel.almeida@xxxxxxxxxxxxx>
>> Reviewed-by: Daniel Almeida <daniel.almeida@xxxxxxxxxxxxx>
>> Signed-off-by: Danilo Krummrich <dakr@xxxxxxxxxx>
>> ---
>> 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);
>
> Copy-paste mistake, obviously this return statement shouldn't be here.
>
>> +}
>> +
>> +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..7ec3341bb411
>> --- /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()) };

This is a problematic API. ioremap() does not work on some platforms
like Apple Silicon. Instead, you have to use ioremap_np() for most devices.

Please add a bindings::resource abstraction and use that to construct
IoMem. Then, you can check the flags for
bindings::IORESOURCE_MEM_NONPOSTED and use the appropriate function,
like this:

https://github.com/AsahiLinux/linux/blob/fce34c83f1dca5b10cc2c866fd8832a362de7974/rust/kernel/io_mem.rs#L152

>> +/// 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(raw: &IoRaw<SIZE>) -> &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 5702ce32ec8e..6c836ab73771 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;
>>
>> --
>> 2.47.1
>>
>
>

~~ Lina

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