From d055768429b3a49090e5f633fa45d7b964fc23ec Mon Sep 17 00:00:00 2001 From: Lyude Paul Date: Fri, 12 Jun 2026 15:43:34 -0400 Subject: [PATCH] rust: drm: gem: shmem: Add vmap functions 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. Signed-off-by: Lyude Paul Reviewed-by: Alexandre Courbot Reviewed-by: Alice Ryhl Acked-by: Danilo Krummrich Link: https://patch.msgid.link/20260612194436.585385-3-lyude@redhat.com --- rust/kernel/drm/gem/shmem.rs | 338 ++++++++++++++++++++++++++++++++++- 1 file changed, 337 insertions(+), 1 deletion(-) diff --git a/rust/kernel/drm/gem/shmem.rs b/rust/kernel/drm/gem/shmem.rs index 090c5d869fdb..a38c98add3d1 100644 --- a/rust/kernel/drm/gem/shmem.rs +++ b/rust/kernel/drm/gem/shmem.rs @@ -20,6 +20,11 @@ Registered, // }, error::to_result, + io::{ + Io, + IoCapable, + IoKnownSize, // + }, prelude::*, sync::aref::ARef, types::{ @@ -28,7 +33,9 @@ }, }; use core::{ + ffi::c_void, marker::PhantomData, + mem::MaybeUninit, // ops::{ Deref, DerefMut, // @@ -39,6 +46,7 @@ }, }; use gem::{ + BaseObject, BaseObjectPrivate, DriverObject, IntoGEMObject, // @@ -200,6 +208,79 @@ extern "C" fn free_callback(obj: *mut bindings::drm_gem_object) { // SAFETY: We're recovering the Kbox<> we created in gem_create_object() let _ = unsafe { KBox::from_raw(this) }; } + + /// Attempt to create a vmap from the gem object, and confirm the size of said vmap. + fn make_vmap<'a, R, const SIZE: usize>(&'a self) -> Result> + where + R: Deref + From<&'a Self>, + { + // INVARIANT: We check here that the gem object is at least as large as `SIZE`. + if self.size() < SIZE { + return Err(ENOSPC); + } + + let mut map: MaybeUninit = MaybeUninit::uninit(); + let guard = DmaResvGuard::new(self); + + // SAFETY: `drm_gem_shmem_vmap()` can be called with the DMA reservation lock held. + to_result(unsafe { + bindings::drm_gem_shmem_vmap_locked(self.as_raw_shmem(), map.as_mut_ptr()) + })?; + + // Drop the guard explicitly here, since we may need to call `raw_vunmap()` (which + // re-acquires the lock). + drop(guard); + + // SAFETY: The call to `drm_gem_shmem_vmap_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, guaranteeing that `map` points to a valid + // memory mapping. + unsafe { self.raw_vunmap(map) }; + + Err(ENOTSUPP) + } else { + Ok(VMap { + // INVARIANT: `addr` remains valid for as long as `owner` does, which extends to the + // lifetime of `VMap` itself. + // SAFETY: We checked that this is not an iomem allocation, making it safe to read + // vaddr. + addr: unsafe { map.__bindgen_anon_1.vaddr }, + owner: self.into(), + }) + } + } + + /// Unmap a vmap from the gem object. + /// + /// # Safety + /// + /// - The caller promises that `map` is a valid vmap on this gem object. + /// - The caller promises that the memory pointed to by map will no longer be accesed through + /// this instance. + unsafe fn raw_vunmap(&self, mut map: bindings::iosys_map) { + let _guard = DmaResvGuard::new(self); + + // SAFETY: + // - This function is safe to call with the DMA reservation lock held. + // - The caller promises that `map` is a valid vmap on this gem object. + unsafe { bindings::drm_gem_shmem_vunmap_locked(self.as_raw_shmem(), &mut map) }; + } + + /// Creates and returns a virtual kernel memory mapping for this object. + #[inline] + pub fn vmap(&self) -> Result> { + self.make_vmap() + } + + /// Creates and returns an owned reference to a virtual kernel memory mapping for this object. + #[inline] + pub fn owned_vmap(&self) -> Result> { + self.make_vmap() + } } impl Deref for Object { @@ -263,7 +344,6 @@ struct DmaResvGuard<'a, T: DriverObject, C: DeviceContext = Registered>( impl<'a, T: DriverObject, C: DeviceContext> DmaResvGuard<'a, T, C> { #[inline] - #[expect(unused)] fn new(obj: &'a Object) -> Self { // SAFETY: This lock is initialized throughout the lifetime of `object`. unsafe { bindings::dma_resv_lock(obj.raw_dma_resv(), ptr::null_mut()) }; @@ -279,3 +359,259 @@ fn drop(&mut self) { unsafe { bindings::dma_resv_unlock(self.0.raw_dma_resv()) }; } } + +/// A reference to a virtual mapping for an shmem-based GEM object in kernel address space. +/// +/// # Invariants +/// +/// - The size of `owner` is >= SIZE. +/// - The memory pointed to by `addr` remains valid at least until this object is dropped. +pub struct VMap +where + D: DriverObject, + C: DeviceContext, + R: Deref>, +{ + addr: *mut c_void, + owner: R, +} + +/// An alias type for a reference to a shmem-based GEM object's VMap. +pub type VMapRef<'a, D, C, const SIZE: usize = 0> = VMap, C, SIZE>; + +/// An alias type for an owned reference to a shmem-based GEM object's VMap. +pub type VMapOwned = VMap>, C, SIZE>; + +impl VMap +where + D: DriverObject, + C: DeviceContext, + R: Deref>, +{ + /// Borrows a reference to the object that owns this virtual mapping. + #[inline] + pub fn owner(&self) -> &Object { + &self.owner + } +} + +impl Drop for VMap +where + D: DriverObject, + C: DeviceContext, + R: Deref>, +{ + #[inline] + fn drop(&mut self) { + // SAFETY: + // - Our existence is proof that this map was previously created using self.owner. + // - Since we are in Drop, we are guaranteed that no one will access the memory + // through this mapping after calling this. + unsafe { + self.owner.raw_vunmap(bindings::iosys_map { + is_iomem: false, + __bindgen_anon_1: bindings::iosys_map__bindgen_ty_1 { vaddr: self.addr }, + }) + }; + } +} + +// SAFETY: `addr` points to a valid memory address for as long as `owner` exists, meaning that so +// long as `owner` is `Send` so is `VMap`. +unsafe impl Send for VMap +where + D: DriverObject, + C: DeviceContext, + R: Deref> + Send, +{ +} + +// SAFETY: `addr` points to a valid memory address for as long as `owner` exists, meaning that so +// long as `owner` is `Sync` so is `VMap`. +unsafe impl Sync for VMap +where + D: DriverObject, + C: DeviceContext, + R: Deref> + Sync, +{ +} + +impl Io for VMap +where + D: DriverObject, + C: DeviceContext, + R: Deref>, +{ + #[inline] + fn addr(&self) -> usize { + self.addr as usize + } + + #[inline] + fn maxsize(&self) -> usize { + self.owner.size() + } +} + +impl IoKnownSize for VMap +where + D: DriverObject, + C: DeviceContext, + R: Deref>, +{ + const MIN_SIZE: usize = SIZE; +} + +macro_rules! impl_vmap_io_capable { + ($ty:ty) => { + impl IoCapable<$ty> for VMap + where + D: DriverObject, + C: DeviceContext, + R: Deref>, + { + #[inline] + 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_volatile(ptr) } + } + + #[inline] + 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_volatile(ptr, value) } + } + } + }; +} + +impl_vmap_io_capable!(u8); +impl_vmap_io_capable!(u16); +impl_vmap_io_capable!(u32); +#[cfg(CONFIG_64BIT)] +impl_vmap_io_capable!(u64); + +#[kunit_tests(rust_drm_gem_shmem)] +mod tests { + use super::*; + use crate::{ + drm::{ + self, + UnregisteredDevice, // + }, + faux, + page::PAGE_SIZE, // + }; + + // The bare minimum needed to create a fake drm driver for kunit + + #[pin_data] + struct KunitData {} + struct KunitDriver; + struct KunitFile; + #[pin_data] + struct KunitObject {} + + const INFO: drm::DriverInfo = drm::DriverInfo { + major: 0, + minor: 0, + patchlevel: 0, + name: c"kunit", + desc: c"Kunit", + }; + + impl drm::file::DriverFile for KunitFile { + type Driver = KunitDriver; + + fn open(_dev: &drm::Device) -> Result>> { + Ok(KBox::new(Self, GFP_KERNEL)?.into()) + } + } + + impl gem::DriverObject for KunitObject { + type Driver = KunitDriver; + type Args = (); + + fn new( + _dev: &drm::Device, + _size: usize, + _args: Self::Args, + ) -> impl PinInit { + try_pin_init!(KunitObject {}) + } + } + + #[vtable] + impl drm::Driver for KunitDriver { + type Data = KunitData; + type File = KunitFile; + type Object = Object; + + const INFO: drm::DriverInfo = INFO; + const IOCTLS: &'static [drm::ioctl::DrmIoctlDescriptor] = &[]; + } + + fn create_drm_dev() -> Result<(faux::Registration, UnregisteredDevice)> { + // Create a faux DRM device so we can test gem object creation. + let data = try_pin_init!(KunitData {}); + let dev = faux::Registration::new(c"Kunit", None)?; + let drm = UnregisteredDevice::new(dev.as_ref(), data)?; + + Ok((dev, drm)) + } + + #[test] + fn compile_time_vmap_sizes() -> Result { + let (_dev, drm) = create_drm_dev()?; + + let obj = Object::::new(&drm, PAGE_SIZE, ObjectConfig::default(), ())?; + + // Try creating a normal vmap + obj.vmap::()?; + + // Try creating a vmap that's smaller then the size we specified + let vmap = obj.vmap::<{ PAGE_SIZE - 100 }>()?; + + // Verify the owner matches + assert!(ptr::eq(vmap.owner(), obj.deref())); + + // Verify the max size matches the actual object size + assert_eq!(vmap.maxsize(), PAGE_SIZE); + + // Make sure creating a vmap that's too large fails + assert!(obj.vmap::<{ PAGE_SIZE + 200 }>().is_err()); + + Ok(()) + } + + #[test] + fn vmap_io() -> Result { + let (_dev, drm) = create_drm_dev()?; + + let obj = Object::::new(&drm, PAGE_SIZE, ObjectConfig::default(), ())?; + + let vmap = obj.vmap::()?; + + vmap.write8(0xDE, 0x0); + assert_eq!(vmap.read8(0x0), 0xDE); + vmap.write32(0xFEDCBA98, 0x20); + + assert_eq!(vmap.read32(0x20), 0xFEDCBA98); + + // Ensure the ordering in memory is correct + let expected = 0xFEDCBA98_u32.to_ne_bytes().into_iter(); + for (offset, expected) in (0x20..=0x23).zip(expected) { + assert_eq!(vmap.read8(offset), expected); + } + + Ok(()) + } +}