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(dsl-hkibng22-54f8dc-251.dhcp.inet.fi. [84.248.220.251]) by smtp.gmail.com with ESMTPSA id 2adb3069b0e04-549ba865024sm1387506e87.123.2025.03.17.11.54.07 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 17 Mar 2025 11:54:07 -0700 (PDT) From: Abdiel Janulgue To: rust-for-linux@vger.kernel.org, daniel.almeida@collabora.com, dakr@kernel.org, robin.murphy@arm.com, aliceryhl@google.com Cc: Miguel Ojeda , Alex Gaynor , Boqun Feng , Gary Guo , =?UTF-8?q?Bj=C3=B6rn=20Roy=20Baron?= , Benno Lossin , Andreas Hindborg , Trevor Gross , Valentin Obst , linux-kernel@vger.kernel.org (open list), Christoph Hellwig , Marek Szyprowski , airlied@redhat.com, iommu@lists.linux.dev (open list:DMA MAPPING HELPERS), Abdiel Janulgue Subject: [PATCH v15 02/11] rust: add dma coherent allocator abstraction. Date: Mon, 17 Mar 2025 20:52:09 +0200 Message-ID: <20250317185345.2608976-3-abdiel.janulgue@gmail.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20250317185345.2608976-1-abdiel.janulgue@gmail.com> References: <20250317185345.2608976-1-abdiel.janulgue@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Add a simple dma coherent allocator rust abstraction. Based on Andreas Hindborg's dma abstractions from the rnvme driver, which was also based on earlier work by Wedson Almeida Filho. Reviewed-by: Alice Ryhl Signed-off-by: Abdiel Janulgue --- rust/bindings/bindings_helper.h | 1 + rust/kernel/dma.rs | 387 ++++++++++++++++++++++++++++++++ rust/kernel/lib.rs | 1 + 3 files changed, 389 insertions(+) create mode 100644 rust/kernel/dma.rs diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helpe= r.h index ae39fc18a8bf..ccb988340df6 100644 --- a/rust/bindings/bindings_helper.h +++ b/rust/bindings/bindings_helper.h @@ -12,6 +12,7 @@ #include #include #include +#include #include #include #include diff --git a/rust/kernel/dma.rs b/rust/kernel/dma.rs new file mode 100644 index 000000000000..9d00f9c49f47 --- /dev/null +++ b/rust/kernel/dma.rs @@ -0,0 +1,387 @@ +// SPDX-License-Identifier: GPL-2.0 + +//! Direct memory access (DMA). +//! +//! C header: [`include/linux/dma-mapping.h`](srctree/include/linux/dma-ma= pping.h) + +use crate::{ + bindings, build_assert, + device::Device, + error::code::*, + error::Result, + transmute::{AsBytes, FromBytes}, + types::ARef, +}; + +/// Possible attributes associated with a DMA mapping. +/// +/// They can be combined with the operators `|`, `&`, and `!`. +/// +/// Values can be used from the [`attrs`] module. +/// +/// # Examples +/// +/// ``` +/// use kernel::device::Device; +/// use kernel::dma::{attrs::*, CoherentAllocation}; +/// +/// # fn test(dev: &Device) -> Result { +/// let attribs =3D DMA_ATTR_FORCE_CONTIGUOUS | DMA_ATTR_NO_WARN; +/// let c: CoherentAllocation =3D +/// CoherentAllocation::alloc_attrs(dev, 4, GFP_KERNEL, attribs)?; +/// # Ok::<(), Error>(()) } +/// ``` +#[derive(Clone, Copy, PartialEq)] +#[repr(transparent)] +pub struct Attrs(u32); + +impl Attrs { + /// Get the raw representation of this attribute. + pub(crate) fn as_raw(self) -> crate::ffi::c_ulong { + self.0 as _ + } + + /// Check whether `flags` is contained in `self`. + pub fn contains(self, flags: Attrs) -> bool { + (self & flags) =3D=3D flags + } +} + +impl core::ops::BitOr for Attrs { + type Output =3D Self; + fn bitor(self, rhs: Self) -> Self::Output { + Self(self.0 | rhs.0) + } +} + +impl core::ops::BitAnd for Attrs { + type Output =3D Self; + fn bitand(self, rhs: Self) -> Self::Output { + Self(self.0 & rhs.0) + } +} + +impl core::ops::Not for Attrs { + type Output =3D Self; + fn not(self) -> Self::Output { + Self(!self.0) + } +} + +/// DMA mapping attributes. +pub mod attrs { + use super::Attrs; + + /// Specifies that reads and writes to the mapping may be weakly order= ed, that is that reads + /// and writes may pass each other. + pub const DMA_ATTR_WEAK_ORDERING: Attrs =3D Attrs(bindings::DMA_ATTR_W= EAK_ORDERING); + + /// Specifies that writes to the mapping may be buffered to improve pe= rformance. + pub const DMA_ATTR_WRITE_COMBINE: Attrs =3D Attrs(bindings::DMA_ATTR_W= RITE_COMBINE); + + /// Lets the platform to avoid creating a kernel virtual mapping for t= he allocated buffer. + pub const DMA_ATTR_NO_KERNEL_MAPPING: Attrs =3D Attrs(bindings::DMA_AT= TR_NO_KERNEL_MAPPING); + + /// Allows platform code to skip synchronization of the CPU cache for = the given buffer assuming + /// that it has been already transferred to 'device' domain. + pub const DMA_ATTR_SKIP_CPU_SYNC: Attrs =3D Attrs(bindings::DMA_ATTR_S= KIP_CPU_SYNC); + + /// Forces contiguous allocation of the buffer in physical memory. + pub const DMA_ATTR_FORCE_CONTIGUOUS: Attrs =3D Attrs(bindings::DMA_ATT= R_FORCE_CONTIGUOUS); + + /// This is a hint to the DMA-mapping subsystem that it's probably not= worth the time to try + /// to allocate memory to in a way that gives better TLB efficiency. + pub const DMA_ATTR_ALLOC_SINGLE_PAGES: Attrs =3D Attrs(bindings::DMA_A= TTR_ALLOC_SINGLE_PAGES); + + /// This tells the DMA-mapping subsystem to suppress allocation failur= e reports (similarly to + /// __GFP_NOWARN). + pub const DMA_ATTR_NO_WARN: Attrs =3D Attrs(bindings::DMA_ATTR_NO_WARN= ); + + /// Used to indicate that the buffer is fully accessible at an elevate= d privilege level (and + /// ideally inaccessible or at least read-only at lesser-privileged le= vels). + pub const DMA_ATTR_PRIVILEGED: Attrs =3D Attrs(bindings::DMA_ATTR_PRIV= ILEGED); +} + +/// An abstraction of the `dma_alloc_coherent` API. +/// +/// This is an abstraction around the `dma_alloc_coherent` API which is us= ed to allocate and map +/// large consistent DMA regions. +/// +/// A [`CoherentAllocation`] instance contains a pointer to the allocated = region (in the +/// processor's virtual address space) and the device address which can be= given to the device +/// as the DMA address base of the region. The region is released once [`C= oherentAllocation`] +/// is dropped. +/// +/// # Invariants +/// +/// For the lifetime of an instance of [`CoherentAllocation`], the `cpu_ad= dr` is a valid pointer +/// to an allocated region of consistent memory and `dma_handle` is the DM= A address base of +/// the region. +// TODO +// +// DMA allocations potentially carry device resources (e.g.IOMMU mappings)= , hence for soundness +// reasons DMA allocation would need to be embedded in a `Devres` containe= r, in order to ensure +// that device resources can never survive device unbind. +// +// However, it is neither desirable nor necessary to protect the allocated= memory of the DMA +// allocation from surviving device unbind; it would require RCU read side= critical sections to +// access the memory, which may require subsequent unnecessary copies. +// +// Hence, find a way to revoke the device resources of a `CoherentAllocati= on`, but not the +// entire `CoherentAllocation` including the allocated memory itself. +pub struct CoherentAllocation { + dev: ARef, + dma_handle: bindings::dma_addr_t, + count: usize, + cpu_addr: *mut T, + dma_attrs: Attrs, +} + +impl CoherentAllocation { + /// Allocates a region of `size_of:: * count` of consistent memory. + /// + /// # Examples + /// + /// ``` + /// use kernel::device::Device; + /// use kernel::dma::{attrs::*, CoherentAllocation}; + /// + /// # fn test(dev: &Device) -> Result { + /// let c: CoherentAllocation =3D + /// CoherentAllocation::alloc_attrs(dev, 4, GFP_KERNEL, DMA_ATTR_N= O_WARN)?; + /// # Ok::<(), Error>(()) } + /// ``` + pub fn alloc_attrs( + dev: &Device, + count: usize, + gfp_flags: kernel::alloc::Flags, + dma_attrs: Attrs, + ) -> Result> { + build_assert!( + core::mem::size_of::() > 0, + "It doesn't make sense for the allocated type to be a ZST" + ); + + let size =3D count + .checked_mul(core::mem::size_of::()) + .ok_or(EOVERFLOW)?; + let mut dma_handle =3D 0; + // SAFETY: Device pointer is guaranteed as valid by the type invar= iant on `Device`. + let ret =3D unsafe { + bindings::dma_alloc_attrs( + dev.as_raw(), + size, + &mut dma_handle, + gfp_flags.as_raw(), + dma_attrs.as_raw(), + ) + }; + if ret.is_null() { + return Err(ENOMEM); + } + // INVARIANT: We just successfully allocated a coherent region whi= ch is accessible for + // `count` elements, hence the cpu address is valid. We also hold = a refcounted reference + // to the device. + Ok(Self { + dev: dev.into(), + dma_handle, + count, + cpu_addr: ret as *mut T, + dma_attrs, + }) + } + + /// Performs the same functionality as [`CoherentAllocation::alloc_att= rs`], except the + /// `dma_attrs` is 0 by default. + pub fn alloc_coherent( + dev: &Device, + count: usize, + gfp_flags: kernel::alloc::Flags, + ) -> Result> { + CoherentAllocation::alloc_attrs(dev, count, gfp_flags, Attrs(0)) + } + + /// Returns the base address to the allocated region in the CPU's virt= ual address space. + pub fn start_ptr(&self) -> *const T { + self.cpu_addr + } + + /// Returns the base address to the allocated region in the CPU's virt= ual address space as + /// a mutable pointer. + pub fn start_ptr_mut(&mut self) -> *mut T { + self.cpu_addr + } + + /// Returns a DMA handle which may given to the device as the DMA addr= ess base of + /// the region. + pub fn dma_handle(&self) -> bindings::dma_addr_t { + self.dma_handle + } + + /// Returns a pointer to an element from the region with bounds checki= ng. `offset` is in + /// units of `T`, not the number of bytes. + /// + /// Public but hidden since it should only be used from [`dma_read`] a= nd [`dma_write`] macros. + #[doc(hidden)] + pub fn item_from_index(&self, offset: usize) -> Result<*mut T> { + if offset >=3D self.count { + return Err(EINVAL); + } + // SAFETY: + // - The pointer is valid due to type invariant on `CoherentAlloca= tion` + // and we've just checked that the range and index is within bound= s. + // - `offset` can't overflow since it is smaller than `self.count`= and we've checked + // that `self.count` won't overflow early in the constructor. + Ok(unsafe { self.cpu_addr.add(offset) }) + } + + /// Reads the value of `field` and ensures that its type is [`FromByte= s`]. + /// + /// # Safety + /// + /// This must be called from the [`dma_read`] macro which ensures that= the `field` pointer is + /// validated beforehand. + /// + /// Public but hidden since it should only be used from [`dma_read`] m= acro. + #[doc(hidden)] + pub unsafe fn field_read(&self, field: *const F) -> F { + // SAFETY: + // - By the safety requirements field is valid. + // - Using read_volatile() here is not sound as per the usual rule= s, the usage here is + // a special exception with the following notes in place. When dea= ling with a potential + // race from a hardware or code outside kernel (e.g. user-space pr= ogram), we need that + // read on a valid memory is not UB. Currently read_volatile() is = used for this, and the + // rationale behind is that it should generate the same code as RE= AD_ONCE() which the + // kernel already relies on to avoid UB on data races. Note that t= he usage of + // read_volatile() is limited to this particular case, it cannot b= e used to prevent + // the UB caused by racing between two kernel functions nor do the= y provide atomicity. + unsafe { field.read_volatile() } + } + + /// Writes a value to `field` and ensures that its type is [`AsBytes`]. + /// + /// # Safety + /// + /// This must be called from the [`dma_write`] macro which ensures tha= t the `field` pointer is + /// validated beforehand. + /// + /// Public but hidden since it should only be used from [`dma_write`] = macro. + #[doc(hidden)] + pub unsafe fn field_write(&self, field: *mut F, val: F) { + // SAFETY: + // - By the safety requirements field is valid. + // - Using write_volatile() here is not sound as per the usual rul= es, the usage here is + // a special exception with the following notes in place. When dea= ling with a potential + // race from a hardware or code outside kernel (e.g. user-space pr= ogram), we need that + // write on a valid memory is not UB. Currently write_volatile() i= s used for this, and the + // rationale behind is that it should generate the same code as WR= ITE_ONCE() which the + // kernel already relies on to avoid UB on data races. Note that t= he usage of + // write_volatile() is limited to this particular case, it cannot = be used to prevent + // the UB caused by racing between two kernel functions nor do the= y provide atomicity. + unsafe { field.write_volatile(val) } + } +} + +/// Note that the device configured to do DMA must be halted before this o= bject is dropped. +impl Drop for CoherentAllocation { + fn drop(&mut self) { + let size =3D self.count * core::mem::size_of::(); + // SAFETY: Device pointer is guaranteed as valid by the type invar= iant on `Device`. + // The cpu address, and the dma handle are valid due to the type i= nvariants on + // `CoherentAllocation`. + unsafe { + bindings::dma_free_attrs( + self.dev.as_raw(), + size, + self.cpu_addr as _, + self.dma_handle, + self.dma_attrs.as_raw(), + ) + } + } +} + +/// Reads a field of an item from an allocated region of structs. +/// +/// # Examples +/// +/// ``` +/// use kernel::device::Device; +/// use kernel::dma::{attrs::*, CoherentAllocation}; +/// +/// struct MyStruct { field: u32, } +/// +/// // SAFETY: All bit patterns are acceptable values for `MyStruct`. +/// unsafe impl kernel::transmute::FromBytes for MyStruct{}; +/// // SAFETY: Instances of `MyStruct` have no uninitialized portions. +/// unsafe impl kernel::transmute::AsBytes for MyStruct{}; +/// +/// # fn test(alloc: &kernel::dma::CoherentAllocation) -> Result= { +/// let whole =3D kernel::dma_read!(alloc[2]); +/// let field =3D kernel::dma_read!(alloc[1].field); +/// # Ok::<(), Error>(()) } +/// ``` +#[macro_export] +macro_rules! dma_read { + ($dma:expr, $idx: expr, $($field:tt)*) =3D> {{ + let item =3D $crate::dma::CoherentAllocation::item_from_index(&$dm= a, $idx)?; + // SAFETY: `item_from_index` ensures that `item` is always a valid= pointer and can be + // dereferenced. The compiler also further validates the expressio= n on whether `field` + // is a member of `item` when expanded by the macro. + unsafe { + let ptr_field =3D ::core::ptr::addr_of!((*item) $($field)*); + $crate::dma::CoherentAllocation::field_read(&$dma, ptr_field) + } + }}; + ($dma:ident [ $idx:expr ] $($field:tt)* ) =3D> { + $crate::dma_read!($dma, $idx, $($field)*); + }; + ($($dma:ident).* [ $idx:expr ] $($field:tt)* ) =3D> { + $crate::dma_read!($($dma).*, $idx, $($field)*); + }; +} + +/// Writes to a field of an item from an allocated region of structs. +/// +/// # Examples +/// +/// ``` +/// use kernel::device::Device; +/// use kernel::dma::{attrs::*, CoherentAllocation}; +/// +/// struct MyStruct { member: u32, } +/// +/// // SAFETY: All bit patterns are acceptable values for `MyStruct`. +/// unsafe impl kernel::transmute::FromBytes for MyStruct{}; +/// // SAFETY: Instances of `MyStruct` have no uninitialized portions. +/// unsafe impl kernel::transmute::AsBytes for MyStruct{}; +/// +/// # fn test(alloc: &kernel::dma::CoherentAllocation) -> Result= { +/// kernel::dma_write!(alloc[2].member =3D 0xf); +/// kernel::dma_write!(alloc[1] =3D MyStruct { member: 0xf }); +/// # Ok::<(), Error>(()) } +/// ``` +#[macro_export] +macro_rules! dma_write { + ($dma:ident [ $idx:expr ] $($field:tt)*) =3D> {{ + $crate::dma_write!($dma, $idx, $($field)*); + }}; + ($($dma:ident).* [ $idx:expr ] $($field:tt)* ) =3D> {{ + $crate::dma_write!($($dma).*, $idx, $($field)*); + }}; + ($dma:expr, $idx: expr, =3D $val:expr) =3D> { + let item =3D $crate::dma::CoherentAllocation::item_from_index(&$dm= a, $idx)?; + // SAFETY: `item_from_index` ensures that `item` is always a valid= item. + unsafe { $crate::dma::CoherentAllocation::field_write(&$dma, item,= $val) } + }; + ($dma:expr, $idx: expr, $(.$field:ident)* =3D $val:expr) =3D> { + let item =3D $crate::dma::CoherentAllocation::item_from_index(&$dm= a, $idx)?; + // SAFETY: `item_from_index` ensures that `item` is always a valid= pointer and can be + // dereferenced. The compiler also further validates the expressio= n on whether `field` + // is a member of `item` when expanded by the macro. + unsafe { + let ptr_field =3D ::core::ptr::addr_of_mut!((*item) $(.$field)= *); + $crate::dma::CoherentAllocation::field_write(&$dma, ptr_field,= $val) + } + }; +} diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs index c92497c7c655..001374a96d66 100644 --- a/rust/kernel/lib.rs +++ b/rust/kernel/lib.rs @@ -44,6 +44,7 @@ pub mod device; pub mod device_id; pub mod devres; +pub mod dma; pub mod driver; pub mod error; pub mod faux; --=20 2.43.0