From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (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 BC9E93BB5A for ; Thu, 16 Oct 2025 21:10:52 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.129.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1760649054; cv=none; b=fXuI2LA/mSyZpw8KVSh5Z05rJischopLTgAbyUHNSF1jCAfPUBJ76mIVw0GJpBR7S4UmoyxOtq6eyxQBma+R0De0t9y/RQyETAoo7VdoZ9r8NWn7YIvxiX4BK5Ndggh/bcQenF/yItf6SX7GyWoznPfnejw6yJ6kelhP1CakGSE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1760649054; c=relaxed/simple; bh=JsrNa++AWg94YCM9+t0lxLwMUzksdKIMi6DX192fWwM=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=A9EJhrarTRSQMH/dUlm3UBVERjC6U4f5fpLH9KNoAEJflmh29C8ORLqAxDhYNmHLa+9iiUyy1XXHhHfmPzFoLq9fY5cPTAjq05H+Yi3kMbNojcAdlD1Hk6HTw8tZyFheOZuvBeK5/RYTbrmD6FL9iTOmwPXwTMpoN7FRx3PkrzQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=NZvWwPwI; arc=none smtp.client-ip=170.10.129.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="NZvWwPwI" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1760649051; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=YiZqMUUcsPqXoJ4Y/gJT4nzMg4uzbhGjpmOaMani4ps=; b=NZvWwPwI5Vw0CtpLoprfnbR8lLV8UwyNGpYg9Hr5P49ucQ8ItlFp6HMqdYepe6DzVf/azG qaA6ZCC/J2YbMp3kfgoPNCd4SVZ41lxvNxT7JifJf3rXtcLYwpsXtwCYtr1wsj3EYO3hUf g8r0e1iiWcoTiFcf68tgIeeC0iVsAFQ= Received: from mx-prod-mc-05.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-481-l3K4NhYlM4CV0HC_F3BLmw-1; Thu, 16 Oct 2025 17:10:47 -0400 X-MC-Unique: l3K4NhYlM4CV0HC_F3BLmw-1 X-Mimecast-MFC-AGG-ID: l3K4NhYlM4CV0HC_F3BLmw_1760649045 Received: from mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.4]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-05.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id CE26319560AA; Thu, 16 Oct 2025 21:10:44 +0000 (UTC) Received: from chopper.lan (unknown [10.22.80.252]) by mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 2E402300019F; Thu, 16 Oct 2025 21:10:40 +0000 (UTC) From: Lyude Paul To: dri-devel@lists.freedesktop.org, rust-for-linux@vger.kernel.org, Daniel Almeida , Alice Ryhl Cc: Asahi Lina , Miguel Ojeda , Alex Gaynor , Boqun Feng , Gary Guo , =?UTF-8?q?Bj=C3=B6rn=20Roy=20Baron?= , Benno Lossin , Andreas Hindborg , Trevor Gross , Danilo Krummrich , David Airlie , Simona Vetter , Greg Kroah-Hartman , Asahi Lina , Viresh Kumar , Shankari Anand , linux-kernel@vger.kernel.org (open list) Subject: [PATCH v4 6/9] rust: drm: gem: shmem: Add DRM shmem helper abstraction Date: Thu, 16 Oct 2025 17:08:19 -0400 Message-ID: <20251016210955.2813186-7-lyude@redhat.com> In-Reply-To: <20251016210955.2813186-1-lyude@redhat.com> References: <20251016210955.2813186-1-lyude@redhat.com> Precedence: bulk X-Mailing-List: rust-for-linux@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.4 From: Asahi Lina 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. Signed-off-by: Asahi Lina Signed-off-by: Daniel Almeida Signed-off-by: Lyude Paul --- 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(…)] 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!() Signed-off-by: Lyude Paul --- rust/bindings/bindings_helper.h | 2 + rust/helpers/drm.c | 48 ++++++- rust/kernel/drm/gem/mod.rs | 3 +- rust/kernel/drm/gem/shmem.rs | 219 ++++++++++++++++++++++++++++++++ 4 files changed, 270 insertions(+), 2 deletions(-) create mode 100644 rust/kernel/drm/gem/shmem.rs diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helper.h index 07f79e125c329..ad644f3d62cc3 100644 --- a/rust/bindings/bindings_helper.h +++ b/rust/bindings/bindings_helper.h @@ -33,6 +33,7 @@ #include #include #include +#include #include #include #include @@ -60,6 +61,7 @@ #include #include #include +#include #include #include #include diff --git a/rust/helpers/drm.c b/rust/helpers/drm.c index 450b406c6f273..a4e997d0b4732 100644 --- a/rust/helpers/drm.c +++ b/rust/helpers/drm.c @@ -1,6 +1,7 @@ // SPDX-License-Identifier: GPL-2.0 #include +#include #include #ifdef CONFIG_DRM @@ -20,4 +21,49 @@ __u64 rust_helper_drm_vma_node_offset_addr(struct drm_vma_offset_node *node) return drm_vma_node_offset_addr(node); } -#endif +#ifdef CONFIG_DRM_GEM_SHMEM_HELPER +void rust_helper_drm_gem_shmem_object_free(struct drm_gem_object *obj) +{ + return drm_gem_shmem_object_free(obj); +} + +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); +} + +int rust_helper_drm_gem_shmem_object_pin(struct drm_gem_object *obj) +{ + return drm_gem_shmem_object_pin(obj); +} + +void rust_helper_drm_gem_shmem_object_unpin(struct drm_gem_object *obj) +{ + drm_gem_shmem_object_unpin(obj); +} + +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); +} + +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); +} + +void rust_helper_drm_gem_shmem_object_vunmap(struct drm_gem_object *obj, + struct iosys_map *map) +{ + drm_gem_shmem_object_vunmap(obj, map); +} + +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 f271c9176bca5..0c36c0ae9d8dc 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 = "y")] +pub mod shmem; use crate::{ alloc::flags::*, @@ -207,7 +209,6 @@ fn create_mmap_offset(&self) -> Result { impl BaseObject for T {} /// 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..e151764322006 --- /dev/null +++ b/rust/kernel/drm/gem/shmem.rs @@ -0,0 +1,219 @@ +// 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. + +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. +#[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); + +impl Object { + /// `drm_gem_object_funcs` vtable suitable for GEM shmem objects. + const VTABLE: bindings::drm_gem_object_funcs = 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 { + 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> = 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 = &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 = KBox::into_raw(unsafe { Pin::into_inner_unchecked(new) }); + + // SAFETY: We're taking over the owned refcount from `drm_gem_shmem_init`. + let obj = unsafe { ARef::from_raw(NonNull::new_unchecked(new)) }; + + // Start filling out values from `config` + if let Some(parent_resv) = 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 = 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 = 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 = 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 = unsafe { container_of!(this.cast::>(), Self, obj) }; + + // SAFETY: We're recovering the Kbox<> we created in gem_create_object() + let _ = 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 = 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 = 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 are to dereference + 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: *mut Opaque<_> = + container_of!(obj, bindings::drm_gem_shmem_object, base).cast(); + + &*container_of!(obj, Object, obj) + } + } +} + +impl driver::AllocImpl for Object { + type Driver = T::Driver; + + const ALLOC_OPS: driver::AllocOps = 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, + }; +} -- 2.51.0