[PATCH v8 7/7] rust: drm/gem: Add vmap functions to shmem bindings

[Lyude Paul <lyude@redhat.com>]

One of the more obvious use cases for gem shmem objects is the ability to
create mappings into their contents. So, let's hook this up in our rust
bindings.

Similar to how we handle SGTables, we make sure there's two different types
of mappings: owned mappings (kernel::drm::gem::shmem::VMap) and borrowed
mappings (kernel::drm::gem::shmem::VMapRef).

Signed-off-by: Lyude Paul <lyude@redhat.com>

---
V7:
* Switch over to the new iosys map bindings that use the Io trait
V8:
* Get rid of iosys_map bindings for now, only support non-iomem types
* s/as_shmem()/as_raw_shmem()

 rust/kernel/drm/gem/shmem.rs | 231 ++++++++++++++++++++++++++++++++++-
 1 file changed, 230 insertions(+), 1 deletion(-)

diff --git a/rust/kernel/drm/gem/shmem.rs b/rust/kernel/drm/gem/shmem.rs
index 3fab5d76c197b..33f46fee87332 100644
--- a/rust/kernel/drm/gem/shmem.rs
+++ b/rust/kernel/drm/gem/shmem.rs
@@ -21,6 +21,11 @@
         from_err_ptr,
         to_result, //
     },
+    io::{
+        Io,
+        IoCapable,
+        IoKnownSize, //
+    },
     prelude::*,
     scatterlist,
     types::{
@@ -29,13 +34,22 @@
     }, //
 };
 use core::{
+    ffi::c_void,
+    mem::{
+        self,
+        MaybeUninit, //
+    },
     ops::{
         Deref,
         DerefMut, //
     },
-    ptr::NonNull,
+    ptr::{
+        self,
+        NonNull, //
+    },
 };
 use gem::{
+    BaseObject,
     BaseObjectPrivate,
     DriverObject,
     IntoGEMObject, //
@@ -217,6 +231,82 @@ pub fn owned_sg_table(&self) -> Result<SGTable<T>> {
             _owner: self.into(),
         })
     }
+
+    /// Attempt to create a [`RawIoSysMap`] from the gem object.
+    fn raw_vmap(&self) -> Result<*mut c_void> {
+        let mut map: MaybeUninit<bindings::iosys_map> = MaybeUninit::uninit();
+
+        // SAFETY: drm_gem_shmem_vmap can be called with the DMA reservation lock held
+        to_result(unsafe {
+            // TODO: see top of file
+            bindings::dma_resv_lock(self.raw_dma_resv(), ptr::null_mut());
+            let ret = bindings::drm_gem_shmem_vmap_locked(self.as_raw_shmem(), map.as_mut_ptr());
+            bindings::dma_resv_unlock(self.raw_dma_resv());
+            ret
+        })?;
+
+        // SAFETY: The call to drm_gem_shmem_vunmap_locked succeeded above, so we are guaranteed
+        // that map is properly initialized.
+        let map = unsafe { map.assume_init() };
+
+        // XXX: We don't currently support iomem allocations
+        if map.is_iomem {
+            // SAFETY:
+            // - The vmap operation above succeeded, making it safe to call vunmap
+            // - We checked that this is an iomem allocation, making it safe to read vaddr_iomem
+            unsafe { self.raw_vunmap(map.__bindgen_anon_1.vaddr_iomem) };
+
+            Err(ENOTSUPP)
+        } else {
+            // SAFETY: We checked that this is not an iomem allocation, making it safe to read vaddr
+            Ok(unsafe { map.__bindgen_anon_1.vaddr })
+        }
+    }
+
+    /// Unmap a [`RawIoSysMap`] from the gem object.
+    ///
+    /// # Safety
+    ///
+    /// - The caller promises that addr came from a prior call to [`Self::raw_vmap`] on this gem
+    ///   object.
+    /// - The caller promises that the memory pointed to by addr will no longer be accesed through
+    ///   this instance.
+    unsafe fn raw_vunmap(&self, vaddr: *mut c_void) {
+        let resv = self.raw_dma_resv();
+        let mut map = bindings::iosys_map {
+            is_iomem: false,
+            __bindgen_anon_1: bindings::iosys_map__bindgen_ty_1 { vaddr },
+        };
+
+        // SAFETY:
+        // - This function is safe to call with the DMA reservation lock held
+        // - Our `ARef` is proof that the underlying gem object here is initialized and thus safe to
+        //   dereference.
+        unsafe {
+            // TODO: see top of file
+            bindings::dma_resv_lock(resv, ptr::null_mut());
+            bindings::drm_gem_shmem_vunmap_locked(self.as_raw_shmem(), &mut map);
+            bindings::dma_resv_unlock(resv);
+        }
+    }
+
+    /// Creates and returns a virtual kernel memory mapping for this object.
+    #[inline]
+    pub fn vmap<const SIZE: usize>(&self) -> Result<VMapRef<'_, T, SIZE>> {
+        Ok(VMapRef {
+            addr: self.raw_vmap()?,
+            owner: self,
+        })
+    }
+
+    /// Creates and returns an owned reference to a virtual kernel memory mapping for this object.
+    #[inline]
+    pub fn owned_vmap<const SIZE: usize>(&self) -> Result<VMap<T, SIZE>> {
+        Ok(VMap {
+            addr: self.raw_vmap()?,
+            owner: self.into(),
+        })
+    }
 }
 
 impl<T: DriverObject> Deref for Object<T> {
@@ -268,6 +358,145 @@ impl<T: DriverObject> driver::AllocImpl for Object<T> {
     };
 }
 
+macro_rules! impl_vmap_io_capable {
+    ($impl:ident, $ty:ty $(, $lifetime:lifetime )?) => {
+        impl<$( $lifetime ,)? D: DriverObject, const SIZE: usize> IoCapable<$ty>
+            for $impl<$( $lifetime ,)? D, SIZE>
+        {
+            #[inline(always)]
+            unsafe fn io_read(&self, address: usize) -> $ty {
+                let ptr = address as *mut $ty;
+
+                // SAFETY: The safety contract of `io_read` guarantees that address is a valid
+                // address within the bounds of `Self` of at least the size of $ty, and is properly
+                // aligned.
+                unsafe { ptr::read(ptr) }
+            }
+
+            #[inline(always)]
+            unsafe fn io_write(&self, value: $ty, address: usize) {
+                let ptr = address as *mut $ty;
+
+                // SAFETY: The safety contract of `io_write` guarantees that address is a valid
+                // address within the bounds of `Self` of at least the size of $ty, and is properly
+                // aligned.
+                unsafe { ptr::write(ptr, value) }
+            }
+        }
+    };
+}
+
+// Implement various traits common to both VMap types
+macro_rules! impl_vmap_common {
+    ($impl:ident $(, $lifetime:lifetime )?) => {
+        impl<$( $lifetime ,)? D, const SIZE: usize> $impl<$( $lifetime ,)? D, SIZE>
+        where
+            D: DriverObject,
+        {
+            /// Borrows a reference to the object that owns this virtual mapping.
+            #[inline(always)]
+            pub fn owner(&self) -> &Object<D> {
+                &self.owner
+            }
+        }
+
+        impl<$( $lifetime ,)? D, const SIZE: usize> Drop for $impl<$( $lifetime ,)? D, SIZE>
+        where
+            D: DriverObject,
+        {
+            #[inline(always)]
+            fn drop(&mut self) {
+                // SAFETY: Our existence is proof that this map was previously created using
+                // self.owner
+                unsafe { self.owner.raw_vunmap(self.addr) };
+            }
+        }
+
+        impl<$( $lifetime ,)? D, const SIZE: usize> Io for $impl<$( $lifetime ,)? D, SIZE>
+        where
+            D: DriverObject,
+        {
+            #[inline(always)]
+            fn addr(&self) -> usize {
+                self.addr as usize
+            }
+
+            #[inline(always)]
+            fn maxsize(&self) -> usize {
+                self.owner.size()
+            }
+        }
+
+        impl<$( $lifetime ,)? D, const SIZE: usize> IoKnownSize for $impl<$( $lifetime ,)? D, SIZE>
+        where
+            D: DriverObject,
+        {
+            const MIN_SIZE: usize = SIZE;
+        }
+
+        impl_vmap_io_capable!($impl, u8 $( , $lifetime )?);
+        impl_vmap_io_capable!($impl, u16 $( , $lifetime )?);
+        impl_vmap_io_capable!($impl, u32 $( , $lifetime )?);
+        #[cfg(CONFIG_64BIT)]
+        impl_vmap_io_capable!($impl, u64 $( , $lifetime )?);
+    };
+}
+
+/// An owned reference to a virtual mapping for a shmem-based GEM object in kernel address space.
+///
+/// # Invariants
+///
+/// - The size of `owner` is >= SIZE.
+/// - The memory pointed to by addr is at least as large as `T`.
+/// - The memory pointed to by addr remains valid at least until this object is dropped.
+pub struct VMap<D: DriverObject, const SIZE: usize = 0> {
+    addr: *mut c_void,
+    owner: ARef<Object<D>>,
+}
+
+impl_vmap_common!(VMap);
+
+impl<D: DriverObject, const SIZE: usize> Clone for VMap<D, SIZE> {
+    fn clone(&self) -> Self {
+        // SAFETY: We have a successful vmap already, so this can't fail
+        unsafe { self.owner.owned_vmap().unwrap_unchecked() }
+    }
+}
+
+impl<'a, D: DriverObject, const SIZE: usize> From<VMapRef<'a, D, SIZE>> for VMap<D, SIZE> {
+    fn from(value: VMapRef<'a, D, SIZE>) -> Self {
+        let this = Self {
+            addr: value.addr,
+            owner: value.owner.into(),
+        };
+
+        mem::forget(value);
+        this
+    }
+}
+
+// SAFETY: addr is guaranteed to be valid and accessible for the lifetime of VMap, ensuring its
+// safe to send across threads.
+unsafe impl<D: DriverObject, const SIZE: usize> Send for VMap<D, SIZE> {}
+// SAFETY: addr is guaranteed to be valid and accessible for the lifetime of VMap, ensuring its
+// safe to send across threads.
+unsafe impl<D: DriverObject, const SIZE: usize> Sync for VMap<D, SIZE> {}
+
+/// A borrowed reference to a virtual mapping for a shmem-based GEM object in kernel address space.
+pub struct VMapRef<'a, D: DriverObject, const SIZE: usize = 0> {
+    addr: *mut c_void,
+    owner: &'a Object<D>,
+}
+
+impl_vmap_common!(VMapRef, 'a);
+
+impl<'a, D: DriverObject, const SIZE: usize> Clone for VMapRef<'a, D, SIZE> {
+    fn clone(&self) -> Self {
+        // SAFETY: We have a successful vmap already, so this can't fail
+        unsafe { self.owner.vmap().unwrap_unchecked() }
+    }
+}
+
 /// An owned reference to a scatter-gather table of DMA address spans for a GEM shmem object.
 ///
 /// This object holds an owned reference to the underlying GEM shmem object, ensuring that the
-- 
2.53.0