From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from bali.collaboradmins.com (bali.collaboradmins.com [148.251.105.195]) (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 6C78C2040A6 for ; Mon, 3 Feb 2025 12:13:02 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=148.251.105.195 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1738584784; cv=none; b=irkd6hrRH++F9w7W0dYQzKB3Wi+vRML5oEnkE2zDdT1NSS/6dvnvy7qlljG92vVhBAG02WOdaAUKIImIkSmytV5+YwXBejfPSFL5mSxFhmxuPAtAjo1xt8Sgoax74o6pmyaxAwRHTjaGsGzGcaeLO9z2qk/uGRz8N2JevECBJbo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1738584784; c=relaxed/simple; bh=jNibjm7Z5BWSQUu8aoxS9exwEy1QnRNA66PqXhHW/n0=; h=Date:From:To:Cc:Subject:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=htavn98fFR+nDHOPEE1/21Yxt8Ys+jARlfcZxBR2eGu/S4kEuMhGQcZHzrB+DmMzgxxAFSp/5R+GfbzSBjbjQCDjl5ViLdqCkYw6qvrVv6x7Xc1dtigHF3H2HhkqYhCQDnjptLaVmbMmS5cMf+Mxo5eMrLT60bIBIAx+SxAG/p8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=collabora.com; spf=pass smtp.mailfrom=collabora.com; dkim=pass (2048-bit key) header.d=collabora.com header.i=@collabora.com header.b=W2mK9rsi; arc=none smtp.client-ip=148.251.105.195 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 (2048-bit key) header.d=collabora.com header.i=@collabora.com header.b="W2mK9rsi" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=collabora.com; s=mail; t=1738584780; bh=jNibjm7Z5BWSQUu8aoxS9exwEy1QnRNA66PqXhHW/n0=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=W2mK9rsiqT96jETmYB4MAss0AmacvbxIZEkiLTswofWhb/orWPJMG+zInUFphQbL1 G+4dBpC7krikDrUmXyBhTwdstCY9SAXCRPmD727o9v8fdb5JcS/Nufrdy9X2ptQJ0t haibJYsQoApeqId1JON4SrW5Z5rBmnpKD4DDWIm38MrGDyKujFyMKGkeonYDDRbtys jWBRQkqZuz2mI/E5LpEWspiC8DMdXpxxupL86rkeKl3ufjnu+bg8KmrY5LbHq9rFbX aCLc9ppvUUiqiXVwWnQxxX2g6AIgeR8PAM/zYdjCN2jwwYA+InPVikFtJwE2dRhaay 69LgVvcos9x0w== Received: from localhost (unknown [IPv6:2a01:e0a:2c:6930:5cf4:84a1:2763:fe0d]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) (Authenticated sender: bbrezillon) by bali.collaboradmins.com (Postfix) with ESMTPSA id 76EA717E0239; Mon, 3 Feb 2025 13:12:59 +0100 (CET) Date: Mon, 3 Feb 2025 13:12:52 +0100 From: Boris Brezillon To: Liviu Dudau Cc: Danilo Krummrich , asahi@lists.linux.dev, Asahi Lina , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Simona Vetter , Frank Binns , Matt Coster , Karol Herbst , Lyude Paul , Steven Price , Lucas De Marchi , Thomas =?UTF-8?B?SGVsbHN0csO2bQ==?= , Rodrigo Vivi , dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, nouveau@lists.freedesktop.org, intel-xe@lists.freedesktop.org, akash.goel@arm.com Subject: Re: [PATCH 0/4] drm/gpuvm: Add support for single-page-filled mappings Message-ID: <20250203131252.71a180ea@collabora.com> In-Reply-To: References: <20250202-gpuvm-single-page-v1-0-8cbd44fdcbd4@asahilina.net> <20250203102153.145229e0@collabora.com> Organization: Collabora X-Mailer: Claws Mail 4.3.0 (GTK 3.24.43; x86_64-redhat-linux-gnu) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Mon, 3 Feb 2025 11:23:53 +0000 Liviu Dudau wrote: > On Mon, Feb 03, 2025 at 10:21:53AM +0100, Boris Brezillon wrote: > > +Akash with whom we've been discussing adding a 'REPEAT' mode to > > drm_gpuvm/panthor. > > > > On Sun, 2 Feb 2025 19:53:47 +0100 > > Danilo Krummrich wrote: > > > > > Hi Lina, > > > > > > On Sun, Feb 02, 2025 at 10:34:49PM +0900, Asahi Lina wrote: > > > > Some hardware requires dummy page mappings to efficiently implement > > > > Vulkan sparse features. These mappings consist of the same physical > > > > memory page, repeated for a large range of address space (e.g. 16GiB). > > > > > > > > Add support for this to drm_gpuvm. Currently, drm_gpuvm expects BO > > > > ranges to correspond 1:1 to virtual memory ranges that are mapped, and > > > > does math on the BO offset accordingly. To make single page mappings > > > > work, we need a way to turn off that math, keeping the BO offset always > > > > constant and pointing to the same page (typically BO offset 0). > > > > > > > > To make this work, we need to handle all the corner cases when these > > > > mappings intersect with regular mappings. The rules are simply to never > > > > mix or merge a "regular" mapping with a single page mapping. > > > > > > > > drm_gpuvm has support for a flags field in drm_gpuva objects. This is > > > > normally managed by drivers directly. We can introduce a > > > > DRM_GPUVA_SINGLE_PAGE flag to handle this. However, to make it work, > > > > sm_map and friends need to know ahead of time whether the new mapping is > > > > a single page mapping or not. Therefore, we need to add an argument to > > > > these functions so drivers can provide the flags to be filled into > > > > drm_gpuva.flags. > > > > > > > > These changes should not affect any existing drivers that use drm_gpuvm > > > > other than the API change: > > > > > > > > - imagination: Does not use flags at all > > > > - nouveau: Only uses drm_gpuva_invalidate(), which is only called on > > > > existing drm_gpuva objects (after the map steps) > > > > - panthor: Does not use flags at all > > > > - xe: Does not use drm_gpuva_init_from_op() or > > > > drm_gpuva_remap()/drm_gpuva_map() (which call it). This means that the > > > > flags field of the gpuva object is managed by the driver only, so these > > > > changes cannot clobber it. > > > > > > > > Note that the way this is implemented, drm_gpuvm does not need to know > > > > the GPU page size. It only has to never do math on the BO offset to meet > > > > the requirements. > > > > > > > > I suspect that after this change there could be some cleanup possible in > > > > the xe driver (which right now passes flags around in various > > > > driver-specific ways from the map step through to drm_gpuva objects), > > > > but I'll leave that to the Xe folks. > > > > > > > > Signed-off-by: Asahi Lina > > > > --- > > > > Asahi Lina (4): > > > > drm/gpuvm: Add a flags argument to drm_gpuvm_sm_map[_*] > > > > drm/gpuvm: Plumb through flags into drm_gpuva_op_map > > > > drm/gpuvm: Add DRM_GPUVA_SINGLE_PAGE flag and logic > > > > drm/gpuvm: Plumb through flags into drm_gpuva_init > > > > > > Without looking into any details yet: > > > > > > This is a bit of tricky one, since we're not even close to having a user for > > > this new feature upstream yet, are we? > > > > Actually, we would be interesting in having this feature hooked up in > > panthor. One use case we have is Vulkan sparse bindings, of course. But > > we also have cases where we need to map a dummy page repeatedly on the > > FW side. The approach we've been considering is slightly different: > > pass a DRM_GPUVA_REPEAT_FLAG along with GEM range, so we can repeat a > > range of the GEM (see the below diff, which is completely untested by > > the way), but I think we'd be fine with this SINGLE_PAGE flag. > > Unless I've misunderstood the intent completely, it looks like Xe also wants > something similar although they call it CPU_ADDR_MIRROR for some reason: > > https://lore.kernel.org/r/20250129195212.745731-9-matthew.brost@intel.com At first glance, it doesn't seem related. The Xe stuff looks more like an alloc-on-fault mechanism. SINGLE_PAGE is about mapping a dummy page repeatedly over a virtual address range so that sparse Vulkan images never get a fault when an unbound image region is accessed.