From nobody Sun Feb 8 20:00:08 2026 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 AE59931280C for ; Fri, 6 Feb 2026 22:35:44 +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=1770417344; cv=none; b=aIJ3wBfzTCsyhRruI7n+vSiP47nkRWR67wQ+69g9cPgzosZk8eVVZ7MOhY2eJGeL4Unfuc7nSpYeYjgZUMPhHdlAybxEQPn2an4rlog5Qb0HH1iFSSisj+dqKnZQbJreoMyZKtOpxlvuWjIlJzbfFlSi7BSIoG/l6gKV2V2au74= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770417344; c=relaxed/simple; bh=b48J/ptqFOanvRTrnTd+5tFeDqKjEGau1q1PRJafq5A=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=hPcLc8al6IDx9GhjjYlKn27h/XRAhYIB/OU2g8HDMFmfNCEG7ZWbRG57oMJfyf20OGiJNZ9MOKERzNUxTaEBg2A94VThy8u7ckXw42LcfveE19tJE/Nedcm2hyCdc46eelKSj5acs+X4aRJHvQHQii3UWKVZFpnCZ7Dy7yvVGIs= 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=Cl26vHPp; 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="Cl26vHPp" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1770417343; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=dA4Lr51Wu0u2/st5Gqdw788WXkyCFbCBFmbyJoArlzs=; b=Cl26vHPpdfdFXfU/Rc5fJMAbrh+k8w90lwhZYDwpc3hw685X6vJuAXLJ+2pUc7ugJq+hoi M3UsS6sP/FYl9rybx93ACbOWpAGZUF1f51N3L5Fj7oVRhMfzKN0isARpH9fYxxRqcoIybv 3J+2oqO9LmLS/fUNct/q5ZDycOva1tE= Received: from mx-prod-mc-03.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-227-fVvsHauUPQy471kLmQRcWQ-1; Fri, 06 Feb 2026 17:35:37 -0500 X-MC-Unique: fVvsHauUPQy471kLmQRcWQ-1 X-Mimecast-MFC-AGG-ID: fVvsHauUPQy471kLmQRcWQ_1770417336 Received: from mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.17]) (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-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 0419F1955F27; Fri, 6 Feb 2026 22:35:36 +0000 (UTC) Received: from GoldenWind.redhat.com (unknown [10.22.64.226]) by mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 80C0E19373D8; Fri, 6 Feb 2026 22:35:34 +0000 (UTC) From: Lyude Paul To: linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, rust-for-linux@vger.kernel.org, Danilo Krummrich Cc: nouveau@lists.freedesktop.org, Daniel Almeida , Gary Guo , Benno Lossin , Alexandre Courbot , Janne Grunau Subject: [PATCH v7 5/7] rust: drm: gem: Introduce shmem::SGTable Date: Fri, 6 Feb 2026 17:34:29 -0500 Message-ID: <20260206223431.693765-6-lyude@redhat.com> In-Reply-To: <20260206223431.693765-1-lyude@redhat.com> References: <20260206223431.693765-1-lyude@redhat.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.0 on 10.30.177.17 Content-Type: text/plain; charset="utf-8" Currently we expose the ability to retrieve an SGTable for an shmem gem object using gem::shmem::Object::::sg_table(). However, this only gives us a borrowed reference. This being said - retrieving an SGTable is a fallible operation, and as such it's reasonable that a driver may want to hold onto an SGTable for longer then a reference would allow in order to avoid having to deal with fallibility every time they want to access the SGTable. One such driver with this usecase is the Asahi driver. So to support this, let's introduce shmem::SGTable - which both holds a pointer to the SGTable and a reference to its respective GEM object in order to keep the GEM object alive for as long as the shmem::SGTable. The type can be used identically to a normal SGTable. Signed-off-by: Lyude Paul Reviewed-by: Janne Grunau --- 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 rust/kernel/drm/gem/shmem.rs | 50 ++++++++++++++++++++++++++++++++++++ 1 file changed, 50 insertions(+) diff --git a/rust/kernel/drm/gem/shmem.rs b/rust/kernel/drm/gem/shmem.rs index d9f1a4e95cedc..e511a9b6710e0 100644 --- a/rust/kernel/drm/gem/shmem.rs +++ b/rust/kernel/drm/gem/shmem.rs @@ -197,6 +197,25 @@ pub fn sg_table(&self) -> Result<&scatterlist::SGTable= > { // pointer to a scatterlist Ok(unsafe { scatterlist::SGTable::from_raw(sgt) }) } + + /// Creates (if necessary) and returns an owned reference to a scatter= -gather table of DMA pages + /// for this object. + /// + /// This is the same as [`sg_table`](Self::sg_table), except that it i= nstead returns an + /// [`shmem::SGTable`] which holds a reference to the associated gem o= bject, instead of a + /// reference to an [`scatterlist::SGTable`]. + /// + /// This will pin the object in memory. + /// + /// [`shmem::SGTable`]: SGTable + pub fn owned_sg_table(&self) -> Result> { + Ok(SGTable { + sgt: self.sg_table()?.into(), + // INVARIANT: We take an owned refcount to `self` here, ensuri= ng that `sgt` remains + // valid for as long as this `SGTable`. + _owner: self.into(), + }) + } } =20 impl Deref for Object { @@ -247,3 +266,34 @@ impl driver::AllocImpl for Object { dumb_map_offset: None, }; } + +/// An owned reference to a scatter-gather table of DMA address spans for = a GEM shmem object. +/// +/// This object holds an owned reference to the underlying GEM shmem objec= t, ensuring that the +/// [`scatterlist::SGTable`] referenced by this type remains valid for the= lifetime of this object. +/// +/// # Invariants +/// +/// - `sgt` is kept alive by `_owner`, ensuring it remains valid for as lo= ng as `Self`. +/// - `sgt` corresponds to the owned object in `_owner`. +/// - This object is only exposed in situations where we know the underlyi= ng `SGTable` will not be +/// modified for the lifetime of this object. Thus, it is safe to send/a= ccess this type across +/// threads. +pub struct SGTable { + sgt: NonNull, + _owner: ARef>, +} + +// SAFETY: This object is thread-safe via our type invariants. +unsafe impl Send for SGTable {} +// SAFETY: This object is thread-safe via our type invariants. +unsafe impl Sync for SGTable {} + +impl Deref for SGTable { + type Target =3D scatterlist::SGTable; + + fn deref(&self) -> &Self::Target { + // SAFETY: Creating an immutable reference to this is safe via our= type invariants. + unsafe { self.sgt.as_ref() } + } +} --=20 2.53.0