[PATCH 2/2] drm/gpuvm: rust: add drm_gpuvm_exec support

[Alice Ryhl <aliceryhl@google.com>]

This adds support for simple usage of drm_gpuvm_exec() for locking all
of the dma reservations and adding fences to them. For more complex
usage that does not involve locking all reservations, it is expected
that the ww-mutex abstractions will be used instead.

Signed-off-by: Alice Ryhl <aliceryhl@google.com>
---
 rust/bindings/bindings_helper.h |  2 ++
 rust/helpers/drm_gpuvm.c        |  6 ++++
 rust/kernel/dma_buf/mod.rs      | 17 ++++++++++
 rust/kernel/drm/gpuvm/mod.rs    | 71 +++++++++++++++++++++++++++++++++++++++++
 4 files changed, 96 insertions(+)

diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helper.h
index 1124785e210b..3978682a6f2e 100644
--- a/rust/bindings/bindings_helper.h
+++ b/rust/bindings/bindings_helper.h
@@ -151,6 +151,8 @@ const vm_flags_t RUST_CONST_HELPER_VM_MIXEDMAP = VM_MIXEDMAP;
 const vm_flags_t RUST_CONST_HELPER_VM_HUGEPAGE = VM_HUGEPAGE;
 const vm_flags_t RUST_CONST_HELPER_VM_NOHUGEPAGE = VM_NOHUGEPAGE;
 
+const u32 RUST_CONST_HELPER_DRM_EXEC_INTERRUPTIBLE_WAIT = DRM_EXEC_INTERRUPTIBLE_WAIT;
+
 #if IS_ENABLED(CONFIG_GPU_BUDDY)
 const unsigned long RUST_CONST_HELPER_GPU_BUDDY_RANGE_ALLOCATION = GPU_BUDDY_RANGE_ALLOCATION;
 const unsigned long RUST_CONST_HELPER_GPU_BUDDY_TOPDOWN_ALLOCATION = GPU_BUDDY_TOPDOWN_ALLOCATION;
diff --git a/rust/helpers/drm_gpuvm.c b/rust/helpers/drm_gpuvm.c
index 4130b6325213..30fb1777fbf2 100644
--- a/rust/helpers/drm_gpuvm.c
+++ b/rust/helpers/drm_gpuvm.c
@@ -23,4 +23,10 @@ bool rust_helper_drm_gpuvm_is_extobj(struct drm_gpuvm *gpuvm,
 	return drm_gpuvm_is_extobj(gpuvm, obj);
 }
 
+__rust_helper
+void rust_helper_drm_gpuvm_exec_unlock(struct drm_gpuvm_exec *vm_exec)
+{
+	drm_gpuvm_exec_unlock(vm_exec);
+}
+
 #endif // CONFIG_RUST_DRM_GPUVM
diff --git a/rust/kernel/dma_buf/mod.rs b/rust/kernel/dma_buf/mod.rs
index b66e747c35ad..234936ba8265 100644
--- a/rust/kernel/dma_buf/mod.rs
+++ b/rust/kernel/dma_buf/mod.rs
@@ -5,3 +5,20 @@
 pub mod dma_fence;
 
 pub use self::dma_fence::Fence;
+
+/// How the fences from a `dma_resv` obj are used.
+///
+/// Please see [the C-side documentation][dma_resv_usage] for more details.
+///
+/// [dma_resv_usage]: https://docs.kernel.org/driver-api/dma-buf.html#c.dma_resv_usage
+#[repr(u32)]
+pub enum DmaResvUsage {
+    /// For in kernel memory management only (e.g. copying, clearing memory).
+    Kernel = bindings::dma_resv_usage_DMA_RESV_USAGE_KERNEL,
+    /// Implicit write synchronization for userspace submissions.
+    Write = bindings::dma_resv_usage_DMA_RESV_USAGE_WRITE,
+    /// Implicit read synchronization for userspace submissions.
+    Read = bindings::dma_resv_usage_DMA_RESV_USAGE_READ,
+    /// No implicit sync (e.g. preemption fences, page table updates, TLB flushes).
+    Bookkeep = bindings::dma_resv_usage_DMA_RESV_USAGE_BOOKKEEP,
+}
diff --git a/rust/kernel/drm/gpuvm/mod.rs b/rust/kernel/drm/gpuvm/mod.rs
index ae58f6f667c1..a52fb25f22ff 100644
--- a/rust/kernel/drm/gpuvm/mod.rs
+++ b/rust/kernel/drm/gpuvm/mod.rs
@@ -16,6 +16,7 @@
         Flags as AllocFlags, //
     },
     bindings,
+    dma_buf::{DmaResvUsage, Fence},
     drm,
     drm::gem::IntoGEMObject,
     error::to_result,
@@ -216,6 +217,30 @@ pub fn obtain(
         Ok(GpuVmBoAlloc::new(self, obj, data)?.obtain())
     }
 
+    /// Prepare this GPUVM.
+    ///
+    /// The parameter indicates how many fences to preallocate space for.
+    #[inline]
+    pub fn prepare(&self, num_fences: u32) -> impl PinInit<GpuVmExec<'_, T>, Error> {
+        try_pin_init!(GpuVmExec {
+            exec <- Opaque::try_ffi_init(|exec: *mut bindings::drm_gpuvm_exec| {
+                // SAFETY: exec is valid but unused memory, so we can write.
+                unsafe {
+                    ptr::write_bytes(exec, 0u8, 1usize);
+                    ptr::write(&raw mut (*exec).vm, self.as_raw());
+                    ptr::write(&raw mut (*exec).flags, bindings::DRM_EXEC_INTERRUPTIBLE_WAIT);
+                    ptr::write(&raw mut (*exec).num_fences, num_fences);
+                }
+
+                // SAFETY: If successful, this `struct drm_gpuvm_exec` remains valid until this is
+                // unlocked because it's pinned and unlocks it in drop. The contained pointer to
+                // `self` remains valid because `GpuVmExec` borrows from `self`.
+                to_result(unsafe { bindings::drm_gpuvm_exec_lock(exec) })
+            }),
+            _gpuvm: PhantomData,
+        })
+    }
+
     /// Clean up buffer objects that are no longer used.
     #[inline]
     pub fn deferred_cleanup(&self) {
@@ -326,3 +351,49 @@ fn deref(&self) -> &GpuVm<T> {
         &self.0
     }
 }
+
+/// The exec token for preparing the objects.
+///
+/// # Invariants
+///
+/// Owns a GPUVM exec context.
+#[pin_data(PinnedDrop)]
+pub struct GpuVmExec<'vm, T: DriverGpuVm> {
+    #[pin]
+    exec: Opaque<bindings::drm_gpuvm_exec>,
+    _gpuvm: PhantomData<&'vm mut GpuVm<T>>,
+}
+
+impl<'vm, T: DriverGpuVm> GpuVmExec<'vm, T> {
+    /// Add a fence.
+    ///
+    /// The caller must ensure that the preallocated space for fences is sufficient.
+    #[inline]
+    pub fn resv_add_fence(
+        &self,
+        fence: &Fence,
+        private_usage: DmaResvUsage,
+        extobj_usage: DmaResvUsage,
+    ) {
+        // SAFETY: This method takes a refcount on the fence, so it's only required to be valid for
+        // the duration of this method. If there is not enough space for the pre-allocated fence,
+        // then this leads to a BUG_ON() but does not trigger UB.
+        unsafe {
+            bindings::drm_gpuvm_resv_add_fence(
+                (*self.exec.get()).vm,
+                &raw mut (*self.exec.get()).exec,
+                fence.as_raw(),
+                private_usage as u32,
+                extobj_usage as u32,
+            )
+        }
+    }
+}
+
+#[pinned_drop]
+impl<'vm, T: DriverGpuVm> PinnedDrop for GpuVmExec<'vm, T> {
+    fn drop(self: Pin<&mut Self>) {
+        // SAFETY: We hold the lock, so it's safe to unlock.
+        unsafe { bindings::drm_gpuvm_exec_unlock(self.exec.get()) };
+    }
+}

-- 
2.54.0.545.g6539524ca2-goog