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To: Abdiel Janulgue Cc: rust-for-linux@vger.kernel.org, Miguel Ojeda , Alex Gaynor , Boqun Feng , Gary Guo , =?UTF-8?Q?Bj=C3=B6rn_Roy_Baron?= , Benno Lossin , Andreas Hindborg , Trevor Gross , Danilo Krummrich , Valentin Obst , open list , Christoph Hellwig , Marek Szyprowski , Robin Murphy , airlied@redhat.com, "open list:DMA MAPPING HELPERS" , Daniel Almeida Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Tue, Dec 10, 2024 at 11:16=E2=80=AFPM Abdiel Janulgue wrote: > > 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: Daniel Almeida > Tested-by: Daniel Almeida > Signed-off-by: Abdiel Janulgue > --- > rust/bindings/bindings_helper.h | 1 + > rust/kernel/dma.rs | 223 ++++++++++++++++++++++++++++++++ > rust/kernel/lib.rs | 1 + > 3 files changed, 225 insertions(+) > create mode 100644 rust/kernel/dma.rs > > diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_hel= per.h > index 5c4dfe22f41a..49bf713b9bb6 100644 > --- a/rust/bindings/bindings_helper.h > +++ b/rust/bindings/bindings_helper.h > @@ -11,6 +11,7 @@ > #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..29ae744d6f2b > --- /dev/null > +++ b/rust/kernel/dma.rs > @@ -0,0 +1,223 @@ > +// SPDX-License-Identifier: GPL-2.0 > + > +//! Direct memory access (DMA). > +//! > +//! C header: [`include/linux/dma-mapping.h`](srctree/include/linux/dma-= mapping.h) > + > +use crate::{ > + bindings, > + build_assert, > + device::Device, > + error::code::*, > + error::Result, > + types::ARef, > + transmute::{AsBytes, FromBytes}, > +}; > + > +/// Possible attributes associated with a DMA mapping. > +/// > +/// They can be combined with the operators `|`, `&`, and `!`. > +/// > +/// Values can be used from the [`attrs`] module. > +#[derive(Clone, Copy, PartialEq)] > +pub struct Attribs(u32); > + > +impl Attribs { > + /// Get the raw representation of this attribute. > + pub(crate) fn as_raw(self) -> u64 { > + self.0.into() > + } > + > + /// Check whether `flags` is contained in `self`. > + pub fn contains(self, flags: Attribs) -> bool { > + (self & flags) =3D=3D flags > + } > +} > + > +impl core::ops::BitOr for Attribs { > + type Output =3D Self; > + fn bitor(self, rhs: Self) -> Self::Output { > + Self(self.0 | rhs.0) > + } > +} > + > +impl core::ops::BitAnd for Attribs { > + type Output =3D Self; > + fn bitand(self, rhs: Self) -> Self::Output { > + Self(self.0 & rhs.0) > + } > +} > + > +impl core::ops::Not for Attribs { > + type Output =3D Self; > + fn not(self) -> Self::Output { > + Self(!self.0) > + } > +} > + > +/// DMA mapping attrributes. > +pub mod attrs { > + use super::Attribs; > + > + /// Specifies that reads and writes to the mapping may be weakly ord= ered, that is that reads > + /// and writes may pass each other. > + pub const DMA_ATTR_WEAK_ORDERING: Attribs =3D Attribs(bindings::DMA_= ATTR_WEAK_ORDERING); > + > + /// Specifies that writes to the mapping may be buffered to improve = performance. > + pub const DMA_ATTR_WRITE_COMBINE: Attribs =3D Attribs(bindings::DMA_= ATTR_WRITE_COMBINE); > + > + /// Lets the platform to avoid creating a kernel virtual mapping for= the allocated buffer. > + pub const DMA_ATTR_NO_KERNEL_MAPPING: Attribs =3D Attribs(bindings::= DMA_ATTR_NO_KERNEL_MAPPING); > + > + /// Allows platform code to skip synchronization of the CPU cache fo= r the given buffer assuming > + /// that it has been already transferred to 'device' domain. > + pub const DMA_ATTR_SKIP_CPU_SYNC: Attribs =3D Attribs(bindings::DMA_= ATTR_SKIP_CPU_SYNC); > + > + /// Forces contiguous allocation of the buffer in physical memory. > + pub const DMA_ATTR_FORCE_CONTIGUOUS: Attribs =3D Attribs(bindings::D= MA_ATTR_FORCE_CONTIGUOUS); > + > + /// This is a hint to the DMA-mapping subsystem that it's probably n= ot worth the time to try > + /// to allocate memory to in a way that gives better TLB efficiency. > + pub const DMA_ATTR_ALLOC_SINGLE_PAGES: Attribs =3D Attribs(bindings:= :DMA_ATTR_ALLOC_SINGLE_PAGES); > + > + /// This tells the DMA-mapping subsystem to suppress allocation fail= ure reports (similarly to > + /// __GFP_NOWARN). > + pub const DMA_ATTR_NO_WARN: Attribs =3D Attribs(bindings::DMA_ATTR_N= O_WARN); > + > + /// Used to indicate that the buffer is fully accessible at an eleva= ted privilege level (and > + /// ideally inaccessible or at least read-only at lesser-privileged = levels). > + pub const DMA_ATTR_PRIVILEGED: Attribs =3D Attribs(bindings::DMA_ATT= R_PRIVILEGED); > +} > + > +/// An abstraction of the `dma_alloc_coherent` API. > +/// > +/// This is an abstraction around the `dma_alloc_coherent` API which is = used to allocate and map > +/// large consistent DMA regions. > +/// > +/// A [`CoherentAllocation`] instance contains a pointer to the allocate= d 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 [= `CoherentAllocation`] > +/// is dropped. > +/// > +/// # Invariants > +/// > +/// For the lifetime of an instance of [`CoherentAllocation`], the cpu a= ddress is a valid pointer > +/// to an allocated region of consistent memory and we hold a reference = to the device. > +pub struct CoherentAllocation { > + dev: ARef, > + dma_handle: bindings::dma_addr_t, > + count: usize, > + cpu_addr: *mut T, > + dma_attrs: Attribs, > +} > + > +impl CoherentAllocation { > + /// Allocates a region of `size_of:: * count` of consistent memor= y. > + /// > + /// # Examples > + /// > + /// ``` > + /// use kernel::device::Device; > + /// use kernel::dma::{attrs::*, CoherentAllocation}; > + /// > + /// # fn test(dev: &Device) -> Result { > + /// let c: CoherentAllocation =3D CoherentAllocation::alloc_att= rs(dev, 4, GFP_KERNEL, > + /// = DMA_ATTR_NO_WARN)?; > + /// # Ok::<(), Error>(()) } > + /// ``` > + pub fn alloc_attrs( > + dev: &Device, > + count: usize, > + gfp_flags: kernel::alloc::Flags, > + dma_attrs: Attribs, > + ) -> Result> { > + build_assert!(core::mem::size_of::() > 0, > + "It doesn't make sense for the allocated type to b= e 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 invariant on= `Device`. > + // We ensure that we catch the failure on this function and thro= w an ENOMEM > + 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 w= hich is accessible for > + // `count` elements, hence the cpu address is valid. We also hol= d 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 `alloc_attrs`, except the `dm= a_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, Attribs(0= )) > + } Please run rustfmt. > + /// Returns the base address to the allocated region and the dma han= dle. The caller takes > + /// ownership of the returned resources. > + pub fn into_parts(self) -> (usize, bindings::dma_addr_t) { > + let ret =3D (self.cpu_addr as _, self.dma_handle); > + core::mem::forget(self); > + ret > + } Not only does this skip the destructor of `dma_free_attrs`. It also skips the destructor of fields including the `dev` field. Did you intend to leave the refcount on `struct device` without decrementing it? > + /// Returns the base address to the allocated region in the CPU's vi= rtual address space. > + pub fn start_ptr(&self) -> *const T { > + self.cpu_addr as _ This conversion happens without needing a cast. > + } > + > + /// Returns the base address to the allocated region in the CPU's vi= rtual 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 ad= dress base of > + /// the region. > + pub fn dma_handle(&self) -> bindings::dma_addr_t { > + self.dma_handle > + } > + > + /// Returns the CPU-addressable region as a slice. > + pub fn cpu_buf(&self) -> &[T] > + { > + // SAFETY: The pointer is valid due to type invariant on `Cohere= ntAllocation` and > + // is valid for reads for `self.count * size_of::` bytes. > + unsafe { core::slice::from_raw_parts(self.cpu_addr, self.count) = } Immutable slices require that the data does not change while the reference is live. Is that the case? If so, your safety comment should explain that. > + } > + > + /// Performs the same functionality as `cpu_buf`, except that a muta= ble slice is returned. > + pub fn cpu_buf_mut(&mut self) -> &mut [T] > + { > + // SAFETY: The pointer is valid due to type invariant on `Cohere= ntAllocation` and > + // is valid for reads for `self.count * size_of::` bytes. > + unsafe { core::slice::from_raw_parts_mut(self.cpu_addr, self.cou= nt) } Mutable slices require that the data is not written to *or read* by anybody else while the reference is live. Is that the case? If so, your safety comment should explain that. > + } > +} > + > +impl Drop for CoherentAllocation { > + fn drop(&mut self) { > + let size =3D self.count * core::mem::size_of::(); > + // SAFETY: the device, cpu address, and the dma handle is valid = due to the > + // type invariants on `CoherentAllocation`. > + unsafe { bindings::dma_free_attrs(self.dev.as_raw(), size, > + self.cpu_addr as _, > + self.dma_handle, > + self.dma_attrs.as_raw(),) } > + } > +} > diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs > index e1065a7551a3..6e90ebf5a130 100644 > --- a/rust/kernel/lib.rs > +++ b/rust/kernel/lib.rs > @@ -35,6 +35,7 @@ > mod build_assert; > pub mod cred; > pub mod device; > +pub mod dma; > pub mod error; > #[cfg(CONFIG_RUST_FW_LOADER_ABSTRACTIONS)] > pub mod firmware; > -- > 2.43.0 >