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 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Get rid of iosys_map bindings for now, only support non-iomem types * s/as_shmem()/as_raw_shmem() V9: * Get rid of some outdated comments I missed * Add missing SIZE check to raw_vmap() * Add a proper unit test that ensures that we actually validate SIZE at compile-time. Turns out it takes only 34 lines to make a boilerplate DRM driver for a kunit test :) * Add unit tests * Add some missing #[inline]s V10: * Correct issue with iomem error path We previously called raw_vunmap() if we got an iomem allocation, but raw_vunmap() was written such that it assumed all allocations were sysmem allocations. Fix this by just making raw_vunmap() accept a iosys_map. V11: * Use Alexandre's clever solution to remove the macros we were using for maintaining two different VMap types. * Change the order of items in Object<T> to ensure that sgt_res is always dropped before obj. * Fix typo in Object.raw_vmap() * s/raw_vmap()/make_vmap()/ Deduplicate code a bit more as well by using more generics here V15: * Add these patches back * We only have one VMap type now! * Use ObjectConfig::default() in unit tests since we unbroke it. V16: * Fix huge rebase error I made and did not notice that squashed 1.5 patches together that were definitely not supposed to be squashed * Update old commit message

rust/kernel/drm/gem/shmem.rs | 303 ++++++++++++++++++++++++++++++++++- 1 file changed, 302 insertions(+), 1 deletion(-)

diff --git a/rust/kernel/drm/gem/shmem.rs b/rust/kernel/drm/gem/shmem.rs index 066a820b0bffc..843869056b1d7 100644 --- a/rust/kernel/drm/gem/shmem.rs +++ b/rust/kernel/drm/gem/shmem.rs @@ -18,11 +18,18 @@ Device, // }, error::to_result, + io::{ + Io, + IoCapable, + IoKnownSize, // + }, prelude::*, sync::aref::ARef, types::Opaque, // }; use core::{ + ffi::c_void, + mem::MaybeUninit, // ops::{ Deref, DerefMut, // @@ -33,6 +40,7 @@ }, }; use gem::{ + BaseObject, BaseObjectPrivate, DriverObject, IntoGEMObject, // @@ -177,6 +185,80 @@ 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<VMap<T, R, SIZE>> + where + R: Deref<Target = Self> + 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: MaybeUninitbindings::iosys_map = 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. + // - We checked that this is an iomem allocation, making it safe to read vaddr_iomem + unsafe { self.raw_vunmap(map) }; + + Err(ENOTSUPP) + } else { + Ok(VMap { + // 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. + // - Our `ARef` is proof that the underlying gem object here is initialized and thus safe to + // dereference. + 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<const SIZE: usize>(&self) -> Result<VMapRef<'_, T, SIZE>> { + self.make_vmap() + } + + /// 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<VMapOwned<T, SIZE>> { + self.make_vmap() + } }

impl<T: DriverObject> Deref for Object<T> { @@ -237,7 +319,6 @@ impl<T: DriverObject> driver::AllocImpl for Object<T> {

impl<'a, T: DriverObject> DmaResvGuard<'a, T> { #[inline(always)] - #[expect(unused)] fn new(obj: &'a Object<T>) -> Self { // SAFETY: This lock is initialized throughout the lifetime of `object`. unsafe { bindings::dma_resv_lock(obj.raw_dma_resv(), ptr::null_mut()) }; @@ -253,3 +334,223 @@ fn drop(&mut self) { unsafe { bindings::dma_resv_unlock(self.0.raw_dma_resv()) }; } } + +macro_rules! impl_vmap_io_capable { + ($impl:ident, $ty:ty) => { + impl<D, R, const SIZE: usize> IoCapable<$ty> for $impl<D, R, SIZE> + where + D: DriverObject, + R: Deref<Target = Object<D>>, + { + #[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) } + } + } + }; +} + +/// 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<D, R, const SIZE: usize = 0> +where + D: DriverObject, + R: Deref<Target = Object<D>>, +{ + 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, const SIZE: usize = 0> = VMap<D, &'a Object<D>, SIZE>; + +/// An alias type for an owned reference to a shmem-based GEM object's VMap. +pub type VMapOwned<D, const SIZE: usize = 0> = VMap<D, ARef<Object<D>>, SIZE>; + +impl<D, R, const SIZE: usize> VMap<D, R, SIZE> +where + D: DriverObject, + R: Deref<Target = Object<D>>, +{ + /// Borrows a reference to the object that owns this virtual mapping. + #[inline(always)] + pub fn owner(&self) -> &Object<D> { + &self.owner + } +} + +impl<D, R, const SIZE: usize> Drop for VMap<D, R, SIZE> +where + D: DriverObject, + R: Deref<Target = Object<D>>, +{ + #[inline(always)] + 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 }, + }) + }; + } +} + +impl<D, R, const SIZE: usize> Io for VMap<D, R, SIZE> +where + D: DriverObject, + R: Deref<Target = Object<D>>, +{ + #[inline(always)] + fn addr(&self) -> usize { + self.addr as usize + } + + #[inline(always)] + fn maxsize(&self) -> usize { + self.owner.size() + } +} + +impl<D, R, const SIZE: usize> IoKnownSize for VMap<D, R, SIZE> +where + D: DriverObject, + R: Deref<Target = Object<D>>, +{ + const MIN_SIZE: usize = SIZE; +} + +impl_vmap_io_capable!(VMap, u8); +impl_vmap_io_capable!(VMap, u16); +impl_vmap_io_capable!(VMap, u32); +#[cfg(CONFIG_64BIT)] +impl_vmap_io_capable!(VMap, u64); + +#[kunit_tests(rust_drm_gem_shmem)] +mod tests { + use super::*; + use crate::{ + drm, + 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<KunitDriver>) -> Result<Pin<KBox<Self>>> { + Ok(KBox::new(Self, GFP_KERNEL)?.into()) + } + } + + impl gem::DriverObject for KunitObject { + type Driver = KunitDriver; + type Args = (); + + fn new( + _dev: &drm::Device<KunitDriver>, + _size: usize, + _args: Self::Args, + ) -> impl PinInit<Self, Error> { + try_pin_init!(KunitObject {}) + } + } + + #[vtable] + impl drm::Driver for KunitDriver { + type Data = KunitData; + type File = KunitFile; + type Object = Object<KunitObject>; + + const INFO: drm::DriverInfo = INFO; + const IOCTLS: &'static [drm::ioctl::DrmIoctlDescriptor] = &[]; + } + + fn create_drm_dev() -> Result<(faux::Registration, ARef<drm::Device<KunitDriver>>)> { + // 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 = drm::Device::<KunitDriver>::new(dev.as_ref(), data)?; + + Ok((dev, drm)) + } + + #[test] + fn compile_time_vmap_sizes() -> Result { + let (_dev, drm) = create_drm_dev()?; + + let obj = Object::<KunitObject>::new(&drm, PAGE_SIZE, ObjectConfig::default(), ())?; + + // Try creating a normal vmap + obj.vmap::<PAGE_SIZE>()?; + + // Try creating a vmap that's smaller then the size we specified + obj.vmap::<{ PAGE_SIZE - 100 }>()?; + + // 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::<KunitObject>::new(&drm, PAGE_SIZE, ObjectConfig::default(), ())?; + + let vmap = obj.vmap::<PAGE_SIZE>()?; + + vmap.write8(0xDE, 0x0); + assert_eq!(vmap.read8(0x0), 0xDE); + vmap.write32(0xFFFFFFFF, 0x20); + + assert_eq!(vmap.read32(0x20), 0xFFFFFFFF); + + assert_eq!(vmap.read8(0x20), 0xFF); + assert_eq!(vmap.read8(0x21), 0xFF); + assert_eq!(vmap.read8(0x22), 0xFF); + assert_eq!(vmap.read8(0x23), 0xFF); + + Ok(()) + } +}

I completely forgot when coming up with this type that #[derive(Default)] only works if all generics mentioned in the type implement Default (and T usually doesn't). This being said: We don't use `T` for anything besides using it for a reference type, so whether or not it implements `Default` shouldn't actually need to matter.

So, fix this by just manually implementing Default instead of deriving it.

Signed-off-by: Lyude Paul lyude@redhat.com --- rust/kernel/drm/gem/shmem.rs | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/rust/kernel/drm/gem/shmem.rs b/rust/kernel/drm/gem/shmem.rs index 843869056b1d7..d8bda8c8e2fb2 100644 --- a/rust/kernel/drm/gem/shmem.rs +++ b/rust/kernel/drm/gem/shmem.rs @@ -50,7 +50,6 @@ /// /// This is used with [`Object::new()`] to control various properties that can only be set when /// initially creating a shmem-backed GEM object. -#[derive(Default)] pub struct ObjectConfig<'a, T: DriverObject> { /// Whether to set the write-combine map flag. pub map_wc: bool, @@ -61,6 +60,16 @@ pub struct ObjectConfig<'a, T: DriverObject> { pub parent_resv_obj: Option<&'a Object<T>>, }

+impl<'a, T: DriverObject> Default for ObjectConfig<'a, T> { + #[inline(always)] + fn default() -> Self { + Self { + map_wc: false, + parent_resv_obj: None, + } + } +} + /// A shmem-backed GEM object. /// /// # Invariants

In order to do this, we need to be careful to ensure that any interface we expose for scatterlists ensures that any mappings created from one are destroyed on driver-unbind. To do this, we introduce a Devres resource into shmem::Object that we use in order to ensure that we release any SGTable mappings on driver-unbind.

There's some other slightly unfortunate caveats of this:

* Drivers don't have explicit control at the moment over when unmapping happens (which is exactly the same as the C side atm, so it might not be a problem). * We can't just return `SGTableMap` to the user through an Arc to attempt to fix the last caveat - because that implies the gem object would need to hold a reference count to the scatterlist mapping, which just leaves us with the same problem.

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

--- V3: * Rename OwnedSGTable to shmem::SGTable. Since the current version of the SGTable abstractions now has a `Owned` and `Borrowed` variant, I think renaming this to shmem::SGTable makes things less confusing. We do however, keep the name of owned_sg_table() as-is. V4: * Clarify safety comments for SGTable to explain why the object is thread-safe. * Rename from SGTableRef to SGTable V10: * Use Devres in order to ensure that SGTables are revocable, and are unmapped on driver-unbind. V11: * s/create_sg_table()/get_sg_table() * Get rid of extraneous `ret = ` in shmem::Object::get_sg_table() V12: * Actually move sgt_res in this patch and not the next one V13: * Use DmaResvGuard suggestion from Alexander * Use Alexander's (much better) solution for get_sg_table() * Use SetOnce instead of UnsafeCell * s/SGTableRef/SGTableMap * Fix typo in SGTableMap documentation * Create fallible constructor for SGTableMap * Don't reuse dma_resv lock for protecting Object contents, just use Mutex + SetOnce * Drop use of drm_gem_shmem_get_pages_sgt_locked(), since we don't need to hold the dma_resv lock ourselves for anything but this function. * Check that the device we receive in the bounds for sg_table() and owned_sg_table() that said Device is in fact, the correct device. * Remove redundant docs in owned_sg_table(), just point it back to sg_table(). * Implement Deborah's suggestion to fix double-free in free_callback() * Restore original order of Object<T> * Fix doc typo for SGTableMap V14: * Use new InitOnce container over the Mutex/SetOnce horror show we had before. * Start using LazyInit container for storing Devres for sgt unmap * Add some kunit tests for sg_table (not sure why I didn't do this before) using some of the boilerplate code leftover from the vmap bindings * Get rid of the owned SGTable variant for now, we'll add it back in a future patch if people actually need it. * Use new LazyInit container from me to get rid of the horrid Mutex<SetOnce<>> mess. * Add the best we can do for unit tests w/r/t SGTable at the moment V16: * Get rid of LazyInit, go back to SetOnce, use trick that Alice recommended that is a lot cleaner. * Fix horrid rebasing mistake

rust/kernel/drm/gem/shmem.rs | 164 +++++++++++++++++++++++++++++++++-- 1 file changed, 155 insertions(+), 9 deletions(-)

diff --git a/rust/kernel/drm/gem/shmem.rs b/rust/kernel/drm/gem/shmem.rs index d8bda8c8e2fb2..5f27e8d59e765 100644 --- a/rust/kernel/drm/gem/shmem.rs +++ b/rust/kernel/drm/gem/shmem.rs @@ -11,20 +11,34 @@

use crate::{ container_of, + device::{ + self, + Bound, // + }, + devres::*, drm::{ driver, gem, private::Sealed, Device, // }, - error::to_result, + error::{ + from_err_ptr, + to_result, // + }, io::{ Io, IoCapable, IoKnownSize, // }, prelude::*, - sync::aref::ARef, + scatterlist, + sync::{ + aref::ARef, + new_mutex, + Mutex, + SetOnce, // + }, types::Opaque, // }; use core::{ @@ -83,6 +97,11 @@ pub struct Object<T: DriverObject> { obj: Opaquebindings::drm_gem_shmem_object, /// Parent object that owns this object's DMA reservation object. parent_resv_obj: Option<ARef<Object<T>>>, + /// Devres object for unmapping any SGTable on driver-unbind. + sgt_res: SetOnce<Devres<SGTableMap<T>>>, + #[pin] + /// Lock for protecting initialization of `sgt_res`. + sgt_lock: Mutex<()>, #[pin] inner: T, } @@ -135,6 +154,8 @@ pub fn new( try_pin_init!(Self { obj <- Opaque::init_zeroed(), parent_resv_obj: config.parent_resv_obj.map(|p| p.into()), + sgt_res: SetOnce::new(), + sgt_lock <- new_mutex!(()), inner <- T::new(dev, size, args), }), GFP_KERNEL, @@ -178,18 +199,23 @@ extern "C" fn free_callback(obj: *mut bindings::drm_gem_object) { // - DRM always passes a valid gem object here // - We used drm_gem_shmem_create() in our create_gem_object callback, so we know that // `obj` is contained within a drm_gem_shmem_object - let this = unsafe { container_of!(obj, bindings::drm_gem_shmem_object, base) }; - - // SAFETY: - // - We're in free_callback - so this function is safe to call. - // - We won't be using the gem resources on `this` after this call. - unsafe { bindings::drm_gem_shmem_release(this) }; + let base = unsafe { container_of!(obj, bindings::drm_gem_shmem_object, base) };

// SAFETY: // - We verified above that `obj` is valid, which makes `this` valid // - This function is set in AllocOps, so we know that `this` is contained within a // `Object<T>` - let this = unsafe { container_of!(Opaque::cast_from(this), Self, obj) }.cast_mut(); + let this = unsafe { container_of!(Opaque::cast_from(base), Self, obj) }.cast_mut(); + + // We need to drop `sgt_res` first, since doing so requires that the GEM object is still + // alive. + // SAFETY: We verified above that `this` is valid. + unsafe { &mut (*this).sgt_res }.reset(); + + // SAFETY: + // - We're in free_callback - so this function is safe to call. + // - We won't be using the gem resources on `this` after this call. + unsafe { bindings::drm_gem_shmem_release(base) };

// SAFETY: We're recovering the Kbox<> we created in gem_create_object() let _ = unsafe { KBox::from_raw(this) }; @@ -268,6 +294,45 @@ pub fn vmap<const SIZE: usize>(&self) -> Result<VMapRef<'_, T, SIZE>> { pub fn owned_vmap<const SIZE: usize>(&self) -> Result<VMapOwned<T, SIZE>> { self.make_vmap() } + + /// Creates (if necessary) and returns an immutable reference to a scatter-gather table of DMA + /// pages for this object. + /// + /// This will pin the object in memory. It is expected that `dev` should be a pointer to the + /// same [`device::Device`] which `self` belongs to, otherwise this function will return + /// `Err(EINVAL)`. + pub fn sg_table<'a>( + &'a self, + dev: &'a device::Device<Bound>, + ) -> Result<&'a scatterlist::SGTable> { + if dev.as_raw() != self.dev().as_ref().as_raw() { + return Err(EINVAL); + } + + let sgt_res = 'out: { + // Fast path: sgt_res is already initialized + if let Some(sgt_res) = self.sgt_res.as_ref() { + break 'out sgt_res; + } + + // Slow path: Grab the lock and see if we need to initialize sgt_res. + let _guard = self.sgt_lock.lock(); + + // If someone initialized it while we were waiting, we can exit early. + if let Some(sgt_res) = self.sgt_res.as_ref() { + break 'out sgt_res; + } + + // If not, finish initializing and return. + self.sgt_res + .populate(Devres::new(dev, SGTableMap::new(self))?); + + // SAFETY: We just populated sgt_res above. + unsafe { self.sgt_res.as_ref().unwrap_unchecked() } + }; + + Ok(sgt_res.access(dev)?) + } }

impl<T: DriverObject> Deref for Object<T> { @@ -457,6 +522,63 @@ impl<D, R, const SIZE: usize> IoKnownSize for VMap<D, R, SIZE> #[cfg(CONFIG_64BIT)] impl_vmap_io_capable!(VMap, u64);

+/// A reference to a GEM object that is known to have a mapped [`SGTable`]. +/// +/// This is used by the Rust bindings with [`Devres`] in order to ensure that mappings for SGTables +/// on GEM shmem objects are revoked on driver-unbind. +/// +/// # Invariants +/// +/// - `self.obj` always points to a valid GEM object. +/// - This object is proof that `self.obj.owner.sgt` has an initialized and valid +/// [`scatterlist::SGTable`]. +pub struct SGTableMap<T: DriverObject> { + obj: NonNull<Object<T>>, +} + +impl<T: DriverObject> Deref for SGTableMap<T> { + type Target = scatterlist::SGTable; + + fn deref(&self) -> &Self::Target { + // SAFETY: + // - The NonNull is guaranteed to be valid via our type invariants. + // - The sgt field is guaranteed to be initialized and valid via our type invariants. + unsafe { scatterlist::SGTable::from_raw((*self.obj.as_ref().as_raw_shmem()).sgt) } + } +} + +impl<T: DriverObject> Drop for SGTableMap<T> { + fn drop(&mut self) { + // SAFETY: `obj` is always valid via our type invariants + let obj = unsafe { self.obj.as_ref() }; + let _lock = DmaResvGuard::new(obj); + + // SAFETY: We acquired the lock needed for calling this function above + unsafe { bindings::__drm_gem_shmem_free_sgt_locked(obj.as_raw_shmem()) }; + } +} + +impl<T: DriverObject> SGTableMap<T> { + fn new(obj: &Object<T>) -> impl Init<Self, Error> { + // INVARIANT: + // - We call drm_gem_shmem_get_pages_sgt_locked below and check whether or not it + // succeeds, fulfilling the invariant of SGTableMap that the object's `sgt` field is + // initialized. + // SAFETY: + // - `obj` is fully initialized, making this function safe to call. + from_err_ptr(unsafe { bindings::drm_gem_shmem_get_pages_sgt(obj.as_raw_shmem()) })?; + + Ok(Self { obj: obj.into() }) + } +} + +// SAFETY: The NonNull in SGTableMap is guaranteed valid by our type invariants, and the GEM object +// it points to is guaranteed to be thread-safe. +unsafe impl<T: DriverObject> Send for SGTableMap<T> {} +// SAFETY: The NonNull in SGTableMap is guaranteed valid by our type invariants, and the GEM object +// it points to is guaranteed to be thread-safe. +unsafe impl<T: DriverObject> Sync for SGTableMap<T> {} + #[kunit_tests(rust_drm_gem_shmem)] mod tests { use super::*; @@ -562,4 +684,28 @@ fn vmap_io() -> Result {

Ok(()) } + + // TODO: I would love to actually test the success paths of sg_table(), but that would require + // also implementing dummy dma_ops so that trying to create a mapping doesn't explode. So, leave + // that for someone else. + + // Ensures that passing the wrong device to sg_table() fails as we expect, and also ensure it + // skips initializing `sgt_res` since we could otherwise create `sgt_res` with the wrong device + // bound to it. + #[test] + fn fail_sg_table_on_wrong_dev() -> Result { + let (_dev, drm) = create_drm_dev()?; + let wrong_dev = faux::Registration::new(c"EvilKunit", None)?; + + let obj = Object::<KunitObject>::new(&drm, PAGE_SIZE, ObjectConfig::default(), ())?; + + assert_eq!(obj.sg_table(wrong_dev.as_ref()).err().unwrap(), EINVAL); + + // If sgt_res was not initialized mistakenly with the wrong device, this should still fail. + assert_eq!(obj.sg_table(wrong_dev.as_ref()).err().unwrap(), EINVAL); + + // TODO: Someday, we should test that creating an sg_table here still succeeds. + + Ok(()) + } }