From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from sender4-pp-f112.zoho.com (sender4-pp-f112.zoho.com [136.143.188.112]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id D47BF19C546; Tue, 17 Feb 2026 19:39:08 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=pass smtp.client-ip=136.143.188.112 ARC-Seal:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1771357150; cv=pass; b=FMRt4/pjR6gnDmoXSy12FRYIjCJojBhXysAghmQyiBPn8MzwPtiIDxzMbi1BsBLB4K9v9Hddbvql2kGJKsTFiKaF6rusXyiUIJw7mYCq6MARLo8dsySxGBPLaF82BssqeQuA5w+fVVCQSLMlBSVGW1fJOGexaFNGk7wFfINlLPM= ARC-Message-Signature:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1771357150; c=relaxed/simple; bh=10+ox2xf8+togaQSB/SOjXMz6cKkm9ywGwVA7tarKrE=; h=Content-Type:Mime-Version:Subject:From:In-Reply-To:Date:Cc: Message-Id:References:To; b=HU/j7SXRXOmwsFq//Em+x+KkqnO71MO1p9dw6aFuVP/gePmPI8jdaCUb6s5UJYtlefKiQjwOLv8+jakRgP3ybPmi3wmmnuTBLVXe5PVY1+W2psjylcvKZHRgZpJYKLLekwtkStoWC4PQu/6Ienfd3gvC3xDgnDJEVUEXuoSC2Kk= ARC-Authentication-Results:i=2; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=collabora.com; spf=pass smtp.mailfrom=collabora.com; dkim=pass (1024-bit key) header.d=collabora.com header.i=daniel.almeida@collabora.com header.b=E3UO+B5J; arc=pass smtp.client-ip=136.143.188.112 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=collabora.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=collabora.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=collabora.com header.i=daniel.almeida@collabora.com header.b="E3UO+B5J" ARC-Seal: i=1; a=rsa-sha256; t=1771357134; cv=none; d=zohomail.com; s=zohoarc; b=JztFbrSjjb6MGsAMpM4pZ6MGr5vCuB5w2xLlnNRfqNdkMvBlVRR5+YEoowo4fFMsBxRser/lKt6oLUUADtGjwemBE7N0if3fDi3wpqes2QWgRPaSqmkZ3PLX2t5ujM7bsrM75Z5Ixj6dokhm3nWtxR7qQou1g+klXJ4kssIsmn0= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=zohomail.com; s=zohoarc; t=1771357134; h=Content-Type:Content-Transfer-Encoding:Cc:Cc:Date:Date:From:From:In-Reply-To:MIME-Version:Message-ID:References:Subject:Subject:To:To:Message-Id:Reply-To; bh=R7jxlTqhnmOEzf6Ej53/pn/46lcrMPiTXvzN+MXZnqA=; b=EoKowpxJ6ff++1AvX4zueTaRuNJpAFUM/4uYxMKfeQ9WyBM2JDCVp/lWmQY8+2tkcbX6WgzKqQSFEoSbJzq40PkY8bXb2b5sotJANZM1iLKwej/f7S8wjsoCbW6wTkP0ep2nCBRfknkswcbYq4q2yql2ZuVJwTazE54u6ITERZo= ARC-Authentication-Results: i=1; mx.zohomail.com; dkim=pass header.i=collabora.com; spf=pass smtp.mailfrom=daniel.almeida@collabora.com; dmarc=pass header.from= DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; t=1771357134; s=zohomail; d=collabora.com; i=daniel.almeida@collabora.com; h=Content-Type:Mime-Version:Subject:Subject:From:From:In-Reply-To:Date:Date:Cc:Cc:Content-Transfer-Encoding:Message-Id:Message-Id:References:To:To:Reply-To; bh=R7jxlTqhnmOEzf6Ej53/pn/46lcrMPiTXvzN+MXZnqA=; b=E3UO+B5JvK8drGFyFelwxjvo58h3qp5CGzcPE8dcBBJ5JSRSFPEgrkI90IiIpBah ETZOW9elwt767vBN1EExpUATp6f6zEUok5WS5YwzGPSeQr8EO7FTn/9lhkaCH15t37g Oyx+Y04YU66Febp3V8In+9LIVBscfL8OUBsUvJuQ= Received: by mx.zohomail.com with SMTPS id 1771357132881477.74784133148523; Tue, 17 Feb 2026 11:38:52 -0800 (PST) Content-Type: text/plain; charset=utf-8 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 (Mac OS X Mail 16.0 \(3826.700.81\)) Subject: Re: [PATCH v7 4/7] rust: drm: gem: shmem: Add DRM shmem helper abstraction From: Daniel Almeida In-Reply-To: <20260206223431.693765-5-lyude@redhat.com> Date: Tue, 17 Feb 2026 16:38:38 -0300 Cc: linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, rust-for-linux@vger.kernel.org, Danilo Krummrich , nouveau@lists.freedesktop.org, Gary Guo , Benno Lossin , Alexandre Courbot , Janne Grunau Content-Transfer-Encoding: quoted-printable Message-Id: References: <20260206223431.693765-1-lyude@redhat.com> <20260206223431.693765-5-lyude@redhat.com> To: Lyude Paul X-Mailer: Apple Mail (2.3826.700.81) X-ZohoMailClient: External Hi Lyude, > On 6 Feb 2026, at 19:34, Lyude Paul wrote: >=20 > From: Asahi Lina >=20 > The DRM shmem helper includes common code useful for drivers which > allocate GEM objects as anonymous shmem. Add a Rust abstraction for > this. Drivers can choose the raw GEM implementation or the shmem = layer, > depending on their needs. >=20 > Signed-off-by: Asahi Lina > Signed-off-by: Daniel Almeida > Signed-off-by: Lyude Paul >=20 > --- >=20 > V2: > * Use the drm_gem_shmem_init() and drm_gem_shmem_release() that I = extracted > so we can handle memory allocation in rust, which means we no longer = have > to handle freeing rust members of the struct by hand and have a = closer > implementation to the main gem object > (this also gets rid of gem_create_object) > * Get rid of GemObjectRef and UniqueGemObjectRef, we have ARef at = home. > * Use Device in Object > * Cleanup Object::::new() a bit: > * Cleanup safety comment > * Use cast_mut() > * Just import container_of!(), we use it all over anyhow > * mut_shmem() -> as_shmem(), make it safe (there's no reason for being = unsafe) > * Remove any *const and *muts in structs, just use NonNull > * Get rid of the previously hand-rolled sg_table bindings in shmem, = use the > bindings from Abdiel's sg_table patch series > * Add a TODO at the top about DMA reservation APIs and a desire for = WwMutex > * Get rid of map_wc() and replace it with a new ObjectConfig struct. = While > it currently only specifies the map_wc flag, the idea here is that > settings like map_wc() and parent_resv_obj() shouldn't be exposed as > normal functions since the only place where it's safe to set them is > when we're still guaranteed unique access to the GEM object, e.g. = before > returning it to the caller. Using a struct instead of individual > arguments here is mainly because we'll be adding at least one more > argument, and there's enough other gem shmem settings that trying to = add > all of them as individual function arguments in the future would be a = bit > messy. > * Get rid of vm_numa_fields!, Lina didn't like this macro much either = and I > think that it's fine for us to just specify the #[cfg(=E2=80=A6)] = attributes by > hand since we only need to do it twice. > * Set drm_gem_object_funcs.vm_ops directly to drm_gem_shmem_vm_ops, = don't > export the various shmem funcs. I'm not sure why this wasn't possible > before but it seems to work fine now. > V4: > * Switch from OpaqueObject to a normal Object now that we've = removed it > * Remove `dev` from Object, it's redundant as drm_gem_object already = has a > device pointer we can use. > * Use &raw instead of addr_of!() > V5: > * Fix typo in shmem::Object::as_raw() > * Add type invariant around `obj` always being a valid > `drm_gem_shmem_object` for the duration of the lifetime of `Object`. > * Use Opaque::cast_from() instead of unrestricted casts > * Use IS_ENABLED() for gem shmem C helpers. > V7: > * Fix import style > * Don't forget to make Object Send/Sync >=20 > rust/bindings/bindings_helper.h | 2 + > rust/helpers/drm.c | 56 ++++++- > rust/kernel/drm/gem/mod.rs | 5 +- > rust/kernel/drm/gem/shmem.rs | 249 ++++++++++++++++++++++++++++++++ > 4 files changed, 310 insertions(+), 2 deletions(-) > create mode 100644 rust/kernel/drm/gem/shmem.rs >=20 > diff --git a/rust/bindings/bindings_helper.h = b/rust/bindings/bindings_helper.h > index ecf31681df806..c93afbd095e87 100644 > --- a/rust/bindings/bindings_helper.h > +++ b/rust/bindings/bindings_helper.h > @@ -33,6 +33,7 @@ > #include > #include > #include > +#include > #include > #include > #include > @@ -61,6 +62,7 @@ > #include > #include > #include > +#include > #include > #include > #include > diff --git a/rust/helpers/drm.c b/rust/helpers/drm.c > index 450b406c6f273..53ec06879db3d 100644 > --- a/rust/helpers/drm.c > +++ b/rust/helpers/drm.c > @@ -1,6 +1,7 @@ > // SPDX-License-Identifier: GPL-2.0 >=20 > #include > +#include > #include >=20 > #ifdef CONFIG_DRM > @@ -20,4 +21,57 @@ __u64 rust_helper_drm_vma_node_offset_addr(struct = drm_vma_offset_node *node) > return drm_vma_node_offset_addr(node); > } >=20 > -#endif > +#if IS_ENABLED(CONFIG_DRM_GEM_SHMEM_HELPER) > +__rust_helper void > +rust_helper_drm_gem_shmem_object_free(struct drm_gem_object *obj) > +{ > + return drm_gem_shmem_object_free(obj); > +} > + > +__rust_helper void > +rust_helper_drm_gem_shmem_object_print_info(struct drm_printer *p, = unsigned int indent, > + const struct drm_gem_object *obj) > +{ > + drm_gem_shmem_object_print_info(p, indent, obj); > +} > + > +__rust_helper int > +rust_helper_drm_gem_shmem_object_pin(struct drm_gem_object *obj) > +{ > + return drm_gem_shmem_object_pin(obj); > +} > + > +__rust_helper void > +rust_helper_drm_gem_shmem_object_unpin(struct drm_gem_object *obj) > +{ > + drm_gem_shmem_object_unpin(obj); > +} > + > +__rust_helper struct sg_table * > +rust_helper_drm_gem_shmem_object_get_sg_table(struct drm_gem_object = *obj) > +{ > + return drm_gem_shmem_object_get_sg_table(obj); > +} > + > +__rust_helper int > +rust_helper_drm_gem_shmem_object_vmap(struct drm_gem_object *obj, > + struct iosys_map *map) > +{ > + return drm_gem_shmem_object_vmap(obj, map); > +} > + > +__rust_helper void > +rust_helper_drm_gem_shmem_object_vunmap(struct drm_gem_object *obj, > + struct iosys_map *map) > +{ > + drm_gem_shmem_object_vunmap(obj, map); > +} > + > +__rust_helper int > +rust_helper_drm_gem_shmem_object_mmap(struct drm_gem_object *obj, = struct vm_area_struct *vma) > +{ > + return drm_gem_shmem_object_mmap(obj, vma); > +} > + > +#endif /* CONFIG_DRM_GEM_SHMEM_HELPER */ > +#endif /* CONFIG_DRM */ > diff --git a/rust/kernel/drm/gem/mod.rs b/rust/kernel/drm/gem/mod.rs > index 972d50d4342dd..379ae3dfb02f5 100644 > --- a/rust/kernel/drm/gem/mod.rs > +++ b/rust/kernel/drm/gem/mod.rs > @@ -3,6 +3,8 @@ > //! DRM GEM API > //! > //! C header: [`include/drm/drm_gem.h`](srctree/include/drm/drm_gem.h) > +#[cfg(CONFIG_DRM_GEM_SHMEM_HELPER)] > +pub mod shmem; >=20 > use crate::{ > alloc::flags::*, > @@ -50,6 +52,8 @@ unsafe fn dec_ref(obj: core::ptr::NonNull) { > }; > } >=20 > +pub(crate) use impl_aref_for_gem_obj; > + > /// A type alias for retrieving a [`Driver`]s [`DriverFile`] = implementation from its > /// [`DriverObject`] implementation. > /// > @@ -205,7 +209,6 @@ fn create_mmap_offset(&self) -> Result { > impl BaseObject for T {} >=20 > /// Crate-private base operations shared by all GEM object classes. > -#[expect(unused)] > pub(crate) trait BaseObjectPrivate: IntoGEMObject { > /// Return a pointer to this object's dma_resv. > fn raw_dma_resv(&self) -> *mut bindings::dma_resv { > diff --git a/rust/kernel/drm/gem/shmem.rs = b/rust/kernel/drm/gem/shmem.rs > new file mode 100644 > index 0000000000000..d9f1a4e95cedc > --- /dev/null > +++ b/rust/kernel/drm/gem/shmem.rs > @@ -0,0 +1,249 @@ > +// SPDX-License-Identifier: GPL-2.0 > + > +//! DRM GEM shmem helper objects > +//! > +//! C header: = [`include/linux/drm/drm_gem_shmem_helper.h`](srctree/include/linux/drm/drm= _gem_shmem_helper.h) > + > +// TODO: > +// - There are a number of spots here that manually acquire/release = the DMA reservation lock using > +// dma_resv_(un)lock(). In the future we should add support for ww = mutex, expose a method to > +// acquire a reference to the WwMutex, and then use that directly = instead of the C functions here. Right, thanks to Onur we=E2=80=99re pretty close on getting ww_mutex = I=E2=80=99d say. > + > +use crate::{ > + container_of, > + drm::{ > + device, > + driver, > + gem, > + private::Sealed, // > + }, > + error::{ > + from_err_ptr, > + to_result, // > + }, > + prelude::*, > + scatterlist, > + types::{ > + ARef, > + Opaque, // > + }, // > +}; > +use core::{ > + ops::{ > + Deref, > + DerefMut, // > + }, > + ptr::NonNull, > +}; > +use gem::{ > + BaseObjectPrivate, > + DriverObject, > + IntoGEMObject, // > +}; > + > +/// A struct for controlling the creation of shmem-backed GEM = objects. > +/// > +/// 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, > + > + /// Reuse the DMA reservation from another GEM object. > + /// > + /// The newly created [`Object`] will hold an owned refcount to = `parent_resv_obj` if specified. > + pub parent_resv_obj: Option<&'a Object>, > +} > + > +/// A shmem-backed GEM object. > +/// > +/// # Invariants > +/// > +/// `obj` contains a valid initialized `struct drm_gem_shmem_object` = for the lifetime of this > +/// object. > +#[repr(C)] > +#[pin_data] > +pub struct Object { > + #[pin] > + obj: Opaque, > + // Parent object that owns this object's DMA reservation object > + parent_resv_obj: Option>>, > + #[pin] > + inner: T, > +} > + > +super::impl_aref_for_gem_obj!(impl for Object where T: = DriverObject); > + > +// SAFETY: All GEM objects are thread-safe. > +unsafe impl Send for Object {} > + > +// SAFETY: All GEM objects are thread-safe. > +unsafe impl Sync for Object {} > + > +impl Object { > + /// `drm_gem_object_funcs` vtable suitable for GEM shmem objects. > + const VTABLE: bindings::drm_gem_object_funcs =3D = bindings::drm_gem_object_funcs { > + free: Some(Self::free_callback), > + open: Some(super::open_callback::), > + close: Some(super::close_callback::), > + print_info: Some(bindings::drm_gem_shmem_object_print_info), > + export: None, > + pin: Some(bindings::drm_gem_shmem_object_pin), > + unpin: Some(bindings::drm_gem_shmem_object_unpin), > + get_sg_table: = Some(bindings::drm_gem_shmem_object_get_sg_table), > + vmap: Some(bindings::drm_gem_shmem_object_vmap), > + vunmap: Some(bindings::drm_gem_shmem_object_vunmap), > + mmap: Some(bindings::drm_gem_shmem_object_mmap), > + status: None, > + rss: None, > + // SAFETY: `drm_gem_shmem_vm_ops` is static const on the C = side, so immutable references are > + // safe here and such references shall be valid forever > + vm_ops: unsafe { &bindings::drm_gem_shmem_vm_ops }, > + evict: None, > + }; > + > + /// Return a raw pointer to the embedded drm_gem_shmem_object. > + fn as_shmem(&self) -> *mut bindings::drm_gem_shmem_object { nit: I=E2=80=99d shoehorn the term =E2=80=9Craw=E2=80=9D here somehow = because of the pointer. Like as_raw_shmem() or something. > + self.obj.get() > + } > + > + /// Create a new shmem-backed DRM object of the given size. > + /// > + /// Additional config options can be specified using `config`. > + pub fn new( > + dev: &device::Device, > + size: usize, > + config: ObjectConfig<'_, T>, > + args: T::Args, > + ) -> Result> { > + let new: Pin> =3D KBox::try_pin_init( > + try_pin_init!(Self { > + obj <- Opaque::init_zeroed(), > + parent_resv_obj: config.parent_resv_obj.map(|p| = p.into()), > + inner <- T::new(dev, size, args), > + }), > + GFP_KERNEL, > + )?; > + > + // SAFETY: `obj.as_raw()` is guaranteed to be valid by the = initialization above. > + unsafe { (*new.as_raw()).funcs =3D &Self::VTABLE }; > + > + // SAFETY: The arguments are all valid via the type = invariants. > + to_result(unsafe { bindings::drm_gem_shmem_init(dev.as_raw(), = new.as_shmem(), size) })?; > + > + // SAFETY: We never move out of `self`. > + let new =3D KBox::into_raw(unsafe { = Pin::into_inner_unchecked(new) }); > + > + // SAFETY: We're taking over the owned refcount from = `drm_gem_shmem_init`. > + let obj =3D unsafe { = ARef::from_raw(NonNull::new_unchecked(new)) }; > + > + // Start filling out values from `config` > + if let Some(parent_resv) =3D config.parent_resv_obj { > + // SAFETY: We have yet to expose the new gem object = outside of this function, so it is > + // safe to modify this field. > + unsafe { (*obj.obj.get()).base.resv =3D = parent_resv.raw_dma_resv() }; > + } > + > + // SAFETY: We have yet to expose this object outside of this = function, so we're guaranteed > + // to have exclusive access - thus making this safe to hold a = mutable reference to. > + let shmem =3D unsafe { &mut *obj.as_shmem() }; > + shmem.set_map_wc(config.map_wc); > + > + Ok(obj) > + } > + > + /// Returns the `Device` that owns this GEM object. > + pub fn dev(&self) -> &device::Device { > + // SAFETY: `dev` will have been initialized in `Self::new()` = by `drm_gem_shmem_init()`. > + unsafe { device::Device::from_raw((*self.as_raw()).dev) } > + } > + > + extern "C" fn free_callback(obj: *mut bindings::drm_gem_object) { > + // SAFETY: > + // - 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 =3D 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) }; > + > + // 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` > + let this =3D unsafe { container_of!(Opaque::cast_from(this), = Self, obj) }.cast_mut(); > + > + // SAFETY: We're recovering the Kbox<> we created in = gem_create_object() > + let _ =3D unsafe { KBox::from_raw(this) }; > + } > + > + /// 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. > + #[inline] > + pub fn sg_table(&self) -> Result<&scatterlist::SGTable> { > + // SAFETY: > + // - drm_gem_shmem_get_pages_sgt is thread-safe. > + // - drm_gem_shmem_get_pages_sgt returns either a valid = pointer to a scatterlist, or an > + // error pointer. > + let sgt =3D from_err_ptr(unsafe { = bindings::drm_gem_shmem_get_pages_sgt(self.as_shmem()) })?; > + > + // SAFETY: We checked above that `sgt` is not an error = pointer, so it must be a valid > + // pointer to a scatterlist > + Ok(unsafe { scatterlist::SGTable::from_raw(sgt) }) > + } > +} > + > +impl Deref for Object { > + type Target =3D T; > + > + fn deref(&self) -> &Self::Target { > + &self.inner > + } > +} > + > +impl DerefMut for Object { > + fn deref_mut(&mut self) -> &mut Self::Target { > + &mut self.inner > + } > +} > + > +impl Sealed for Object {} > + > +impl gem::IntoGEMObject for Object { > + fn as_raw(&self) -> *mut bindings::drm_gem_object { > + // SAFETY: > + // - Our immutable reference is proof that this is safe to = dereference. > + // - `obj` is always a valid drm_gem_shmem_object via our = type invariants. > + unsafe { &raw mut (*self.obj.get()).base } > + } > + > + unsafe fn from_raw<'a>(obj: *mut bindings::drm_gem_object) -> &'a = Object { > + // SAFETY: The safety contract of from_gem_obj() guarantees = that `obj` is contained within > + // `Self` > + unsafe { > + let obj =3D Opaque::cast_from(container_of!(obj, = bindings::drm_gem_shmem_object, base)); > + > + &*container_of!(obj, Object, obj) > + } > + } > +} > + > +impl driver::AllocImpl for Object { > + type Driver =3D T::Driver; > + > + const ALLOC_OPS: driver::AllocOps =3D driver::AllocOps { > + gem_create_object: None, > + prime_handle_to_fd: None, > + prime_fd_to_handle: None, > + gem_prime_import: None, > + gem_prime_import_sg_table: = Some(bindings::drm_gem_shmem_prime_import_sg_table), > + dumb_create: Some(bindings::drm_gem_shmem_dumb_create), > + dumb_map_offset: None, > + }; > +} > --=20 > 2.53.0 >=20 Looks good to me. Reviewed-by: Daniel Almeida =