rust: io_pgtable: Add io_pgtable abstraction

The io_pgtable subsystem implements page table management for various
IOMMU page table formats. This abstraction allows Rust drivers for
devices with an embedded MMU to use this shared code directly.

Gather structures are not implemented yet, since we don't have a
consumer for that functionality. That can be added and refactored when
someone needs it.

It's worth noting that although this abstraction is nominally used to
manage page tables and mapping physical memory addresses, the
abstraction API itself is not unsafe. This is because, by itself, it can
only be used to manage page tables in isolation, which have no effect on
the system. In Rust, we typically use `unsafe` to mark operations that
actually introduce the safety requirements (that is, where the
responsibilities are created). Here, that would be actually installing
the page table root pointer into a device register (the downstream iomem
abstractions are unsafe for this reason, because devices can do DMA).

Signed-off-by: Asahi Lina <[email protected]>

Author: asahilina

rust/bindings/bindings_helper.h

@@ -9,6 +9,7 @@
 #include <kunit/test.h>
 #include <linux/device.h>
 #include <linux/errname.h>
+#include <linux/io-pgtable.h>
 #include <linux/slab.h>
 #include <linux/refcount.h>
 #include <linux/wait.h>

rust/kernel/io_pgtable.rs

@@ -0,0 +1,351 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! IOMMU page table management
+//!
+//! C header: [`include/io-pgtable.h`](../../../../include/io-pgtable.h)
+
+use crate::{
+    bindings, device,
+    error::{code::*, to_result, Result},
+    types::{ForeignOwnable, ScopeGuard},
+};
+
+use core::marker::PhantomData;
+use core::mem;
+use core::num::NonZeroU64;
+
+/// Protection flags used with IOMMU mappings.
+pub mod prot {
+    /// Read access.
+    pub const READ: u32 = bindings::IOMMU_READ;
+    /// Write access.
+    pub const WRITE: u32 = bindings::IOMMU_WRITE;
+    /// Request cache coherency.
+    pub const CACHE: u32 = bindings::IOMMU_CACHE;
+    /// Request no-execute permission.
+    pub const NOEXEC: u32 = bindings::IOMMU_NOEXEC;
+    /// MMIO peripheral mapping.
+    pub const MMIO: u32 = bindings::IOMMU_MMIO;
+    /// Privileged mapping.
+    pub const PRIV: u32 = bindings::IOMMU_PRIV;
+}
+
+/// Represents a requested io_pgtable configuration.
+pub struct Config {
+    /// Quirk bitmask (type-specific).
+    pub quirks: usize,
+    /// Valid page sizes, as a bitmask of powers of two.
+    pub pgsize_bitmap: usize,
+    /// Input address space size in bits.
+    pub ias: usize,
+    /// Output address space size in bits.
+    pub oas: usize,
+    /// IOMMU uses coherent accesses for page table walks.
+    pub coherent_walk: bool,
+}
+
+/// IOMMU callbacks for TLB and page table management.
+///
+/// Users must implement this trait to perform the TLB flush actions for this IOMMU, if
+/// required.
+pub trait FlushOps {
+    /// User-specified type owned by the IOPagetable that will be passed to TLB operations.
+    type Data: ForeignOwnable + Send + Sync;
+
+    /// Synchronously invalidate the entire TLB context.
+    fn tlb_flush_all(data: <Self::Data as ForeignOwnable>::Borrowed<'_>);
+
+    /// Synchronously invalidate all intermediate TLB state (sometimes referred to as the "walk
+    /// cache") for a virtual address range.
+    fn tlb_flush_walk(
+        data: <Self::Data as ForeignOwnable>::Borrowed<'_>,
+        iova: usize,
+        size: usize,
+        granule: usize,
+    );
+
+    /// Optional callback to queue up leaf TLB invalidation for a single page.
+    ///
+    /// IOMMUs that cannot batch TLB invalidation operations efficiently will typically issue
+    /// them here, but others may decide to update the iommu_iotlb_gather structure and defer
+    /// the invalidation until iommu_iotlb_sync() instead.
+    ///
+    /// TODO: Implement the gather argument for batching.
+    fn tlb_add_page(
+        data: <Self::Data as ForeignOwnable>::Borrowed<'_>,
+        iova: usize,
+        granule: usize,
+    );
+}
+
+/// Inner page table info shared across all table types.
+/// # Invariants
+///
+///   - [`self.ops`] is valid and non-null.
+///   - [`self.cfg`] is valid and non-null.
+#[doc(hidden)]
+pub struct IoPageTableInner {
+    ops: *mut bindings::io_pgtable_ops,
+    cfg: bindings::io_pgtable_cfg,
+    data: *mut core::ffi::c_void,
+}
+
+/// Helper trait to get the config type for a single page table type from the union.
+pub trait GetConfig {
+    /// Returns the specific output configuration for this page table type.
+    fn cfg(iopt: &impl IoPageTable) -> &Self
+    where
+        Self: Sized;
+}
+
+/// A generic IOMMU page table
+pub trait IoPageTable: crate::private::Sealed {
+    #[doc(hidden)]
+    const FLUSH_OPS: bindings::iommu_flush_ops;
+
+    #[doc(hidden)]
+    fn new_fmt<T: FlushOps>(
+        dev: &dyn device::RawDevice,
+        format: u32,
+        config: Config,
+        data: T::Data,
+    ) -> Result<IoPageTableInner> {
+        let ptr = data.into_foreign() as *mut _;
+        let guard = ScopeGuard::new(|| {
+            // SAFETY: `ptr` came from a previous call to `into_foreign`.
+            unsafe { T::Data::from_foreign(ptr) };
+        });
+
+        let mut raw_cfg = bindings::io_pgtable_cfg {
+            quirks: config.quirks.try_into()?,
+            pgsize_bitmap: config.pgsize_bitmap.try_into()?,
+            ias: config.ias.try_into()?,
+            oas: config.oas.try_into()?,
+            coherent_walk: config.coherent_walk,
+            tlb: &Self::FLUSH_OPS,
+            iommu_dev: dev.raw_device(),
+            // SAFETY: This is an output field which is fine to zero-init.
+            __bindgen_anon_1: unsafe { mem::zeroed() },
+        };
+
+        // SAFETY: FFI call, all input pointers are valid.
+        let ops = unsafe {
+            bindings::alloc_io_pgtable_ops(format as bindings::io_pgtable_fmt, &mut raw_cfg, ptr)
+        };
+
+        if ops.is_null() {
+            return Err(EINVAL);
+        }
+
+        guard.dismiss();
+        Ok(IoPageTableInner {
+            ops,
+            cfg: raw_cfg,
+            data: ptr,
+        })
+    }
+
+    /// Map a range of pages.
+    fn map_pages(
+        &mut self,
+        iova: usize,
+        paddr: usize,
+        pgsize: usize,
+        pgcount: usize,
+        prot: u32,
+    ) -> Result<usize> {
+        let mut mapped: usize = 0;
+
+        // SAFETY: FFI call, ops is valid per the type invariant.
+        to_result(unsafe {
+            (*self.inner().ops).map_pages.unwrap()(
+                self.inner().ops,
+                iova as u64,
+                paddr as u64,
+                pgsize,
+                pgcount,
+                prot as i32,
+                bindings::GFP_KERNEL,
+                &mut mapped,
+            )
+        })?;
+
+        Ok(mapped)
+    }
+
+    /// Unmap a range of pages.
+    fn unmap_pages(
+        &mut self,
+        iova: usize,
+        pgsize: usize,
+        pgcount: usize,
+        // TODO: gather: *mut iommu_iotlb_gather,
+    ) -> usize {
+        // SAFETY: FFI call, ops is valid per the type invariant.
+        unsafe {
+            (*self.inner().ops).unmap_pages.unwrap()(
+                self.inner().ops,
+                iova as u64,
+                pgsize,
+                pgcount,
+                core::ptr::null_mut(),
+            )
+        }
+    }
+
+    /// Translate an IOVA to the corresponding physical address, if mapped.
+    fn iova_to_phys(&self, iova: usize) -> Option<NonZeroU64> {
+        // SAFETY: FFI call, ops is valid per the type invariant.
+        NonZeroU64::new(unsafe {
+            (*self.inner().ops).iova_to_phys.unwrap()(self.inner().ops, iova as u64)
+        })
+    }
+
+    #[doc(hidden)]
+    fn inner(&self) -> &IoPageTableInner;
+
+    #[doc(hidden)]
+    fn raw_cfg(&self) -> &bindings::io_pgtable_cfg {
+        &self.inner().cfg
+    }
+}
+
+// SAFETY: All abstraction operations either require mutable references or are thread-safe,
+// and io_pgtable_ops objects can be passed between threads without issue.
+unsafe impl Send for IoPageTableInner {}
+unsafe impl Sync for IoPageTableInner {}
+
+unsafe extern "C" fn tlb_flush_all_callback<T: FlushOps>(cookie: *mut core::ffi::c_void) {
+    // SAFETY: The cookie is always a ForeignOwnable of the right type, per new_fmt().
+    T::tlb_flush_all(unsafe { T::Data::borrow(cookie) });
+}
+
+unsafe extern "C" fn tlb_flush_walk_callback<T: FlushOps>(
+    iova: core::ffi::c_ulong,
+    size: usize,
+    granule: usize,
+    cookie: *mut core::ffi::c_void,
+) {
+    // SAFETY: The cookie is always a ForeignOwnable of the right type, per new_fmt().
+    T::tlb_flush_walk(
+        unsafe { T::Data::borrow(cookie) },
+        iova as usize,
+        size,
+        granule,
+    );
+}
+
+unsafe extern "C" fn tlb_add_page_callback<T: FlushOps>(
+    _gather: *mut bindings::iommu_iotlb_gather,
+    iova: core::ffi::c_ulong,
+    granule: usize,
+    cookie: *mut core::ffi::c_void,
+) {
+    // SAFETY: The cookie is always a ForeignOwnable of the right type, per new_fmt().
+    T::tlb_add_page(unsafe { T::Data::borrow(cookie) }, iova as usize, granule);
+}
+
+macro_rules! iopt_cfg {
+    ($name:ident, $field:ident, $type:ident) => {
+        /// An IOMMU page table configuration for a specific kind of pagetable.
+        pub type $name = bindings::$type;
+
+        impl GetConfig for $name {
+            fn cfg(iopt: &impl IoPageTable) -> &$name {
+                // SAFETY: The type system ensures we are accessing the right union field.
+                unsafe { &iopt.raw_cfg().__bindgen_anon_1.$field }
+            }
+        }
+    };
+}
+
+impl GetConfig for () {
+    fn cfg(_iopt: &impl IoPageTable) -> &() {
+        &()
+    }
+}
+
+macro_rules! iopt_type {
+    ($type:ident, $cfg:ty, $fmt:ident) => {
+        /// Represents an IOPagetable of this type.
+        pub struct $type<T: FlushOps>(IoPageTableInner, PhantomData<T>);
+
+        impl<T: FlushOps> $type<T> {
+            /// Creates a new IOPagetable implementation of this type.
+            pub fn new(dev: &dyn device::RawDevice, config: Config, data: T::Data) -> Result<Self> {
+                Ok(Self(
+                    <Self as IoPageTable>::new_fmt::<T>(dev, bindings::$fmt, config, data)?,
+                    PhantomData,
+                ))
+            }
+
+            /// Get the configuration for this IOPagetable.
+            pub fn cfg(&self) -> &$cfg {
+                <$cfg as GetConfig>::cfg(self)
+            }
+        }
+
+        impl<T: FlushOps> crate::private::Sealed for $type<T> {}
+
+        impl<T: FlushOps> IoPageTable for $type<T> {
+            const FLUSH_OPS: bindings::iommu_flush_ops = bindings::iommu_flush_ops {
+                tlb_flush_all: Some(tlb_flush_all_callback::<T>),
+                tlb_flush_walk: Some(tlb_flush_walk_callback::<T>),
+                tlb_add_page: Some(tlb_add_page_callback::<T>),
+            };
+
+            fn inner(&self) -> &IoPageTableInner {
+                &self.0
+            }
+        }
+
+        impl<T: FlushOps> Drop for $type<T> {
+            fn drop(&mut self) {
+                // SAFETY: The pointer is valid by the type invariant.
+                unsafe { bindings::free_io_pgtable_ops(self.0.ops) };
+
+                // Free context data.
+                //
+                // SAFETY: This matches the call to `into_foreign` from `new_fmt`.
+                unsafe { T::Data::from_foreign(self.0.data) };
+            }
+        }
+    };
+}
+
+// Ew, bindgen unions really are quite messy...
+iopt_cfg!(
+    ARMLPAES1Cfg,
+    arm_lpae_s1_cfg,
+    io_pgtable_cfg__bindgen_ty_1__bindgen_ty_1
+);
+iopt_cfg!(
+    ARMLPAES2Cfg,
+    arm_lpae_s2_cfg,
+    io_pgtable_cfg__bindgen_ty_1__bindgen_ty_2
+);
+iopt_cfg!(
+    ARMv7SCfg,
+    arm_v7s_cfg,
+    io_pgtable_cfg__bindgen_ty_1__bindgen_ty_3
+);
+iopt_cfg!(
+    ARMMaliLPAECfg,
+    arm_mali_lpae_cfg,
+    io_pgtable_cfg__bindgen_ty_1__bindgen_ty_4
+);
+iopt_cfg!(
+    AppleDARTCfg,
+    apple_dart_cfg,
+    io_pgtable_cfg__bindgen_ty_1__bindgen_ty_5
+);
+
+iopt_type!(ARM32LPAES1, ARMLPAES1Cfg, io_pgtable_fmt_ARM_32_LPAE_S1);
+iopt_type!(ARM32LPAES2, ARMLPAES2Cfg, io_pgtable_fmt_ARM_32_LPAE_S2);
+iopt_type!(ARM64LPAES1, ARMLPAES1Cfg, io_pgtable_fmt_ARM_64_LPAE_S1);
+iopt_type!(ARM64LPAES2, ARMLPAES2Cfg, io_pgtable_fmt_ARM_64_LPAE_S2);
+iopt_type!(ARMv7S, ARMv7SCfg, io_pgtable_fmt_ARM_V7S);
+iopt_type!(ARMMaliLPAE, ARMMaliLPAECfg, io_pgtable_fmt_ARM_MALI_LPAE);
+iopt_type!(AMDIOMMUV1, (), io_pgtable_fmt_AMD_IOMMU_V1);
+iopt_type!(AppleDART, AppleDARTCfg, io_pgtable_fmt_APPLE_DART);
+iopt_type!(AppleDART2, AppleDARTCfg, io_pgtable_fmt_APPLE_DART2);

rust/kernel/lib.rs

@@ -37,6 +37,8 @@ pub mod device;
 pub mod error;
 pub mod init;
 pub mod ioctl;
+#[cfg(CONFIG_IOMMU_IO_PGTABLE)]
+pub mod io_pgtable;
 #[cfg(CONFIG_KUNIT)]
 pub mod kunit;
 pub mod prelude;