From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp4.osuosl.org (smtp4.osuosl.org [140.211.166.137]) (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 19AA01386AD for ; Thu, 25 Jan 2024 16:47:29 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=140.211.166.137 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1706201251; cv=none; b=mrRJj/7nOaI3POmz6QRtYvBC5n39FzdRCX9kKfXUhKPmUDM9NOfSywMuBeTIwTyHPYtEYIakcfnmpy6JIwf8zlBQUeZIOA6EnZA+DiBmHvK77AHsO2kU4PB/zov1WnFylPywbApyfkzozb9iVy1eaiC9nVYKsxIpqECeRKXIyxY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1706201251; c=relaxed/simple; bh=5Sz6nyOUKq3MXrhagkP0FYymhM11nOGQSTAzf9cZVGw=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=uTHfgoXnT2jc2W0gYnGDoXQI/gwPViHTpagKcWCDTQKXVhoO9Zup7KvN+9PSiDFPkyDigWcrcuVxDkeV80ZfG+s8WJ4kMyZK7vaf5Z/5w4+yYtN59I5WaM5aKAf8pQT+xhWCagmpSsxQa6JXxMOYdZ7CImk8+rsiT8hVf1L1nys= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; arc=none smtp.client-ip=140.211.166.137 Received: from localhost (localhost [127.0.0.1]) by smtp4.osuosl.org (Postfix) with ESMTP id 5C5B041F27 for ; Thu, 25 Jan 2024 16:47:29 +0000 (UTC) DKIM-Filter: OpenDKIM Filter v2.11.0 smtp4.osuosl.org 5C5B041F27 X-Virus-Scanned: amavisd-new at osuosl.org X-Spam-Flag: NO X-Spam-Score: -4.2 X-Spam-Level: Received: from smtp4.osuosl.org ([127.0.0.1]) by localhost (smtp4.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id JPxxi9_z8izk for ; Thu, 25 Jan 2024 16:47:28 +0000 (UTC) Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp4.osuosl.org (Postfix) with ESMTP id 5F8E541F25 for ; Thu, 25 Jan 2024 16:47:28 +0000 (UTC) DKIM-Filter: OpenDKIM Filter v2.11.0 smtp4.osuosl.org 5F8E541F25 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 2E9401764; Thu, 25 Jan 2024 08:48:12 -0800 (PST) Received: from [10.1.27.41] (e122027.cambridge.arm.com [10.1.27.41]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id AF2673F5A1; Thu, 25 Jan 2024 08:47:24 -0800 (PST) Message-ID: <7144dd9b-62d1-4968-9b94-0313e2475f7e@arm.com> Date: Thu, 25 Jan 2024 16:47:24 +0000 Precedence: bulk X-Mailing-List: virtualization@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v19 18/30] drm/panfrost: Explicitly get and put drm-shmem pages Content-Language: en-GB To: Dmitry Osipenko , David Airlie , Gerd Hoffmann , Gurchetan Singh , Chia-I Wu , Daniel Vetter , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , =?UTF-8?Q?Christian_K=C3=B6nig?= , Qiang Yu , Boris Brezillon , Emma Anholt , Melissa Wen Cc: dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, kernel@collabora.com, virtualization@lists.linux-foundation.org References: <20240105184624.508603-1-dmitry.osipenko@collabora.com> <20240105184624.508603-19-dmitry.osipenko@collabora.com> From: Steven Price In-Reply-To: <20240105184624.508603-19-dmitry.osipenko@collabora.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 05/01/2024 18:46, Dmitry Osipenko wrote: > To simplify the drm-shmem refcnt handling, we're moving away from > the implicit get_pages() that is used by get_pages_sgt(). From now on > drivers will have to pin pages while they use sgt. Panfrost's shrinker > doesn't support swapping out BOs, hence pages are pinned and sgt is valid > as long as pages' use-count > 0. > > In Panfrost, panfrost_gem_mapping, which is the object representing a > GPU mapping of a BO, owns a pages ref. This guarantees that any BO being > mapped GPU side has its pages retained till the mapping is destroyed. > > Since pages are no longer guaranteed to stay pinned for the BO lifetime, > and MADVISE(DONT_NEED) flagging remains after the GEM handle has been > destroyed, we need to add an extra 'is_purgeable' check in > panfrost_gem_purge(), to make sure we're not trying to purge a BO that > already had its pages released. > > Signed-off-by: Dmitry Osipenko Reviewed-by: Steven Price Although I don't like the condition in panfrost_gem_mapping_release() for drm_gem_shmem_put_pages() and assigning NULL to bo->sgts - it feels very fragile. See below. > --- > drivers/gpu/drm/panfrost/panfrost_gem.c | 63 ++++++++++++++----- > .../gpu/drm/panfrost/panfrost_gem_shrinker.c | 6 ++ > 2 files changed, 52 insertions(+), 17 deletions(-) > > diff --git a/drivers/gpu/drm/panfrost/panfrost_gem.c b/drivers/gpu/drm/panfrost/panfrost_gem.c > index f268bd5c2884..7edfc12f7c1f 100644 > --- a/drivers/gpu/drm/panfrost/panfrost_gem.c > +++ b/drivers/gpu/drm/panfrost/panfrost_gem.c > @@ -35,20 +35,6 @@ static void panfrost_gem_free_object(struct drm_gem_object *obj) > */ > WARN_ON_ONCE(!list_empty(&bo->mappings.list)); > > - if (bo->sgts) { > - int i; > - int n_sgt = bo->base.base.size / SZ_2M; > - > - for (i = 0; i < n_sgt; i++) { > - if (bo->sgts[i].sgl) { > - dma_unmap_sgtable(pfdev->dev, &bo->sgts[i], > - DMA_BIDIRECTIONAL, 0); > - sg_free_table(&bo->sgts[i]); > - } > - } > - kvfree(bo->sgts); > - } > - > drm_gem_shmem_free(&bo->base); > } > > @@ -85,11 +71,40 @@ panfrost_gem_teardown_mapping(struct panfrost_gem_mapping *mapping) > > static void panfrost_gem_mapping_release(struct kref *kref) > { > - struct panfrost_gem_mapping *mapping; > - > - mapping = container_of(kref, struct panfrost_gem_mapping, refcount); > + struct panfrost_gem_mapping *mapping = > + container_of(kref, struct panfrost_gem_mapping, refcount); > + struct panfrost_gem_object *bo = mapping->obj; > + struct panfrost_device *pfdev = bo->base.base.dev->dev_private; > > panfrost_gem_teardown_mapping(mapping); > + > + /* On heap BOs, release the sgts created in the fault handler path. */ > + if (bo->sgts) { > + int i, n_sgt = bo->base.base.size / SZ_2M; > + > + for (i = 0; i < n_sgt; i++) { > + if (bo->sgts[i].sgl) { > + dma_unmap_sgtable(pfdev->dev, &bo->sgts[i], > + DMA_BIDIRECTIONAL, 0); > + sg_free_table(&bo->sgts[i]); > + } > + } > + kvfree(bo->sgts); > + } > + > + /* Pages ref is owned by the panfrost_gem_mapping object. We must > + * release our pages ref (if any), before releasing the object > + * ref. > + * Non-heap BOs acquired the pages at panfrost_gem_mapping creation > + * time, and heap BOs may have acquired pages if the fault handler > + * was called, in which case bo->sgts should be non-NULL. > + */ > + if (!bo->base.base.import_attach && (!bo->is_heap || bo->sgts) && > + bo->base.madv >= 0) { > + drm_gem_shmem_put_pages(&bo->base); > + bo->sgts = NULL; The assignment of NULL here really ought to be unconditional - it isn't a valid pointer because of the kvfree() above. I also feel that the big condition above suggests there's a need for a better state machine to keep track of what's going on. But having said that I do think this series as a whole is an improvement, it's nice to get the shrinker code generic. And sadly I don't have an immediate idea for cleaning this up, hence my R-b. Steve > + } > + > drm_gem_object_put(&mapping->obj->base.base); > panfrost_mmu_ctx_put(mapping->mmu); > kfree(mapping); > @@ -125,6 +140,20 @@ int panfrost_gem_open(struct drm_gem_object *obj, struct drm_file *file_priv) > if (!mapping) > return -ENOMEM; > > + if (!bo->is_heap && !bo->base.base.import_attach) { > + /* Pages ref is owned by the panfrost_gem_mapping object. > + * For non-heap BOs, we request pages at mapping creation > + * time, such that the panfrost_mmu_map() call, further down in > + * this function, is guaranteed to have pages_use_count > 0 > + * when drm_gem_shmem_get_pages_sgt() is called. > + */ > + ret = drm_gem_shmem_get_pages(&bo->base); > + if (ret) { > + kfree(mapping); > + return ret; > + } > + } > + > INIT_LIST_HEAD(&mapping->node); > kref_init(&mapping->refcount); > drm_gem_object_get(obj); > diff --git a/drivers/gpu/drm/panfrost/panfrost_gem_shrinker.c b/drivers/gpu/drm/panfrost/panfrost_gem_shrinker.c > index 02b60ea1433a..d4fb0854cf2f 100644 > --- a/drivers/gpu/drm/panfrost/panfrost_gem_shrinker.c > +++ b/drivers/gpu/drm/panfrost/panfrost_gem_shrinker.c > @@ -50,6 +50,12 @@ static bool panfrost_gem_purge(struct drm_gem_object *obj) > if (!dma_resv_trylock(shmem->base.resv)) > goto unlock_mappings; > > + /* BO might have become unpurgeable if the last pages_use_count ref > + * was dropped, but the BO hasn't been destroyed yet. > + */ > + if (!drm_gem_shmem_is_purgeable(shmem)) > + goto unlock_mappings; > + > panfrost_gem_teardown_mappings_locked(bo); > drm_gem_shmem_purge_locked(&bo->base); > ret = true;