drm/asahi: Align kernel range to buffer::PAGE_SIZE

We only require alignment to the UAT page size from userspace, but
internally we need more, so just align it if userspace gives us lower
alignment.

Signed-off-by: Asahi Lina <lina@asahilina.net>

Author: hoshinolina

drivers/gpu/drm/asahi/file.rs

@@ -9,7 +9,10 @@
 
 use crate::debug::*;
 use crate::driver::AsahiDevice;
-use crate::{alloc, buffer, driver, gem, hw, mmu, queue, util::RangeExt};
+use crate::{
+    alloc, buffer, driver, gem, hw, mmu, queue,
+    util::{align, align_down, RangeExt},
+};
 use core::mem::MaybeUninit;
 use core::ops::Range;
 use kernel::dma_fence::RawDmaFence;
@@ -319,7 +322,11 @@ impl File {
             return Err(EINVAL);
         }
 
-        let kernel_half_size = (kernel_range.range() >> 1) & !(mmu::UAT_PGMSK as u64);
+        // Align to buffer::PAGE_SIZE so the allocators are happy
+        let kernel_range = align(kernel_range.start, buffer::PAGE_SIZE as u64)
+            ..align_down(kernel_range.end, buffer::PAGE_SIZE as u64);
+
+        let kernel_half_size = align_down(kernel_range.range() >> 1, buffer::PAGE_SIZE as u64);
         let kernel_gpu_range = kernel_range.start..(kernel_range.start + kernel_half_size);
         let kernel_gpufw_range = kernel_gpu_range.end..kernel_range.end;
 

drivers/gpu/drm/asahi/util.rs

@@ -25,6 +25,26 @@ where
     (a + b - one) & !(b - one)
 }
 
+/// Aligns an integer type down to a power of two.
+pub(crate) fn align_down<T>(a: T, b: T) -> T
+where
+    T: Copy
+        + Default
+        + BitAnd<Output = T>
+        + Not<Output = T>
+        + Sub<Output = T>
+        + Div<Output = T>
+        + core::cmp::PartialEq,
+{
+    let def: T = Default::default();
+    #[allow(clippy::eq_op)]
+    let one: T = !def / !def;
+
+    assert!((b & (b - one)) == def);
+
+    a & !(b - one)
+}
+
 /// Integer division rounding up.
 pub(crate) fn div_ceil<T>(a: T, b: T) -> T
 where