From patchwork Fri May 6 18:02:15 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: Jason Ekstrand X-Patchwork-Id: 12842009 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id EBAAEC433EF for ; Sat, 7 May 2022 13:18:37 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 970651132C1; Sat, 7 May 2022 13:18:20 +0000 (UTC) Received: from mail-ot1-x333.google.com (mail-ot1-x333.google.com [IPv6:2607:f8b0:4864:20::333]) by gabe.freedesktop.org (Postfix) with ESMTPS id 450AE10EFA8 for ; Fri, 6 May 2022 18:02:22 +0000 (UTC) Received: by mail-ot1-x333.google.com with SMTP id s18-20020a056830149200b006063fef3e17so5401735otq.12 for ; Fri, 06 May 2022 11:02:22 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=jlekstrand-net.20210112.gappssmtp.com; s=20210112; h=from:to:cc:subject:date:message-id:in-reply-to:references :mime-version:content-transfer-encoding; bh=0GafE1B3wr5Ikp0fS5Y0kwV7xWfDBxwxYUGA3q3Xjsg=; b=Pb2EBNvwUtyMX+gT7AfB8qT8Nh5aMqjVg4Wq+6zYabDURQm4J0TtAqFXaPfZhb5eIN mmCdDFLwdJLQJnSkvmYxuUkLKx6vxB3fuOdX2glGTvLLlpsxhvhSQfhO3FpQvkTwSLJL K2IbNAvyu4+k9qUp6bqSdcors2LssyKnu+8zD9zjYxQGpiH3ftd312cS/zAGUReS+AeU HshoOqlxs51/2+PCINKK67rfIb7kxUauUzYft/kS9H1UbrwsB7KXw/r9bNnq2HaLcnWw 1TlSuaQ6axBusbgTs3yDYJ8Os5eVuj8NIyzD7ulKioWaVIhnH6ngmAanRxUQYowDCzFi UAuQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=0GafE1B3wr5Ikp0fS5Y0kwV7xWfDBxwxYUGA3q3Xjsg=; b=zKxZxJopfrDZUhmHRGP+AwZ7ixvEZ13uOGdhcTfGFg6adbHLA8dwVQWdUjf6pFoTdD H35Zqu9/CiIUVHk8ThUtqDjw+tlNyM9a19pPKysyx3ftL6SRAdHuKTFcvrWvgpnDFY78 6kVnBPDxJsLJRrD5xqI3UFrmFAYVU168kfZrnlc2T5HPNBI5M2yLJhIa7nMQa/Qfh422 CeM4Jd0w+nVE4tOH7NzlEFDe4Njhl8s6hvwUfEuYLTp3xpWjawGVJdRTOgKF8+xsFaEn 1GWnjhtJ+EE5fcH7/NVWoZmNIv7rq8lj3FnfuB8MtgJsoexyftzYgsDnxsKtZtuDoXNj 2KjA== X-Gm-Message-State: AOAM533ZdRwLxIuWzkNEOr6jjCun5NxZdTv5CSMhDVydAl+Uh1vYR4al IiC3EL9Hian/2GnIONXudE8bYXM3CzvSAA== X-Google-Smtp-Source: ABdhPJxdQ8fsM10Lj1LzXwj1T5A+Q+OEKMMt7Bh74h6sd9uhxT42qUXCVaiyfgD7SZyRurYhafPsfQ== X-Received: by 2002:a9d:3b5:0:b0:603:f8ac:a780 with SMTP id f50-20020a9d03b5000000b00603f8aca780mr1419426otf.26.1651860141070; Fri, 06 May 2022 11:02:21 -0700 (PDT) Received: from animal.lan (2603-8080-2102-63d7-a603-c311-740a-6dbf.res6.spectrum.com. [2603:8080:2102:63d7:a603:c311:740a:6dbf]) by smtp.gmail.com with ESMTPSA id a32-20020a9d2623000000b006060322123csm1840998otb.12.2022.05.06.11.02.19 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 06 May 2022 11:02:20 -0700 (PDT) From: Jason Ekstrand To: dri-devel@lists.freedesktop.org Subject: [PATCH 1/2] dma-buf: Add an API for exporting sync files (v14) Date: Fri, 6 May 2022 13:02:15 -0500 Message-Id: <20220506180216.2095060-2-jason@jlekstrand.net> X-Mailer: git-send-email 2.36.0 In-Reply-To: <20220506180216.2095060-1-jason@jlekstrand.net> References: <20220506180216.2095060-1-jason@jlekstrand.net> MIME-Version: 1.0 X-Mailman-Approved-At: Sat, 07 May 2022 13:18:19 +0000 X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Jason Ekstrand , Sumit Semwal , Jason Ekstrand , Jason Ekstrand , Daniel Vetter , =?utf-8?q?Christian_K=C3=B6nig?= Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" Modern userspace APIs like Vulkan are built on an explicit synchronization model. This doesn't always play nicely with the implicit synchronization used in the kernel and assumed by X11 and Wayland. The client -> compositor half of the synchronization isn't too bad, at least on intel, because we can control whether or not i915 synchronizes on the buffer and whether or not it's considered written. The harder part is the compositor -> client synchronization when we get the buffer back from the compositor. We're required to be able to provide the client with a VkSemaphore and VkFence representing the point in time where the window system (compositor and/or display) finished using the buffer. With current APIs, it's very hard to do this in such a way that we don't get confused by the Vulkan driver's access of the buffer. In particular, once we tell the kernel that we're rendering to the buffer again, any CPU waits on the buffer or GPU dependencies will wait on some of the client rendering and not just the compositor. This new IOCTL solves this problem by allowing us to get a snapshot of the implicit synchronization state of a given dma-buf in the form of a sync file. It's effectively the same as a poll() or I915_GEM_WAIT only, instead of CPU waiting directly, it encapsulates the wait operation, at the current moment in time, in a sync_file so we can check/wait on it later. As long as the Vulkan driver does the sync_file export from the dma-buf before we re-introduce it for rendering, it will only contain fences from the compositor or display. This allows to accurately turn it into a VkFence or VkSemaphore without any over-synchronization. By making this an ioctl on the dma-buf itself, it allows this new functionality to be used in an entirely driver-agnostic way without having access to a DRM fd. This makes it ideal for use in driver-generic code in Mesa or in a client such as a compositor where the DRM fd may be hard to reach. v2 (Jason Ekstrand): - Use a wrapper dma_fence_array of all fences including the new one when importing an exclusive fence. v3 (Jason Ekstrand): - Lock around setting shared fences as well as exclusive - Mark SIGNAL_SYNC_FILE as a read-write ioctl. - Initialize ret to 0 in dma_buf_wait_sync_file v4 (Jason Ekstrand): - Use the new dma_resv_get_singleton helper v5 (Jason Ekstrand): - Rename the IOCTLs to import/export rather than wait/signal - Drop the WRITE flag and always get/set the exclusive fence v6 (Jason Ekstrand): - Drop the sync_file import as it was all-around sketchy and not nearly as useful as import. - Re-introduce READ/WRITE flag support for export - Rework the commit message v7 (Jason Ekstrand): - Require at least one sync flag - Fix a refcounting bug: dma_resv_get_excl() doesn't take a reference - Use _rcu helpers since we're accessing the dma_resv read-only v8 (Jason Ekstrand): - Return -ENOMEM if the sync_file_create fails - Predicate support on IS_ENABLED(CONFIG_SYNC_FILE) v9 (Jason Ekstrand): - Add documentation for the new ioctl v10 (Jason Ekstrand): - Go back to dma_buf_sync_file as the ioctl struct name v11 (Daniel Vetter): - Go back to dma_buf_export_sync_file as the ioctl struct name - Better kerneldoc describing what the read/write flags do v12 (Christian König): - Document why we chose to make it an ioctl on dma-buf v13 (Jason Ekstrand): - Rebase on Christian König's fence rework v14 (Daniel Vetter & Christian König): - Use dma_rev_usage_rw to get the properly inverted usage to pass to dma_resv_get_singleton() - Clean up the sync_file and fd if copy_to_user() fails Signed-off-by: Jason Ekstrand Signed-off-by: Jason Ekstrand Signed-off-by: Jason Ekstrand Acked-by: Simon Ser Acked-by: Christian König Reviewed-by: Daniel Vetter Cc: Sumit Semwal Cc: Maarten Lankhorst Reviewed-by: Christian König for the series. Reviewed-by: Daniel Vetter --- drivers/dma-buf/dma-buf.c | 67 ++++++++++++++++++++++++++++++++++++ include/uapi/linux/dma-buf.h | 35 +++++++++++++++++++ 2 files changed, 102 insertions(+) diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c index 79795857be3e..6ff54f7e6119 100644 --- a/drivers/dma-buf/dma-buf.c +++ b/drivers/dma-buf/dma-buf.c @@ -20,6 +20,7 @@ #include #include #include +#include #include #include #include @@ -192,6 +193,9 @@ static loff_t dma_buf_llseek(struct file *file, loff_t offset, int whence) * Note that this only signals the completion of the respective fences, i.e. the * DMA transfers are complete. Cache flushing and any other necessary * preparations before CPU access can begin still need to happen. + * + * As an alternative to poll(), the set of fences on DMA buffer can be + * exported as a &sync_file using &dma_buf_sync_file_export. */ static void dma_buf_poll_cb(struct dma_fence *fence, struct dma_fence_cb *cb) @@ -326,6 +330,64 @@ static long dma_buf_set_name(struct dma_buf *dmabuf, const char __user *buf) return 0; } +#if IS_ENABLED(CONFIG_SYNC_FILE) +static long dma_buf_export_sync_file(struct dma_buf *dmabuf, + void __user *user_data) +{ + struct dma_buf_export_sync_file arg; + enum dma_resv_usage usage; + struct dma_fence *fence = NULL; + struct sync_file *sync_file; + int fd, ret; + + if (copy_from_user(&arg, user_data, sizeof(arg))) + return -EFAULT; + + if (arg.flags & ~DMA_BUF_SYNC_RW) + return -EINVAL; + + if ((arg.flags & DMA_BUF_SYNC_RW) == 0) + return -EINVAL; + + fd = get_unused_fd_flags(O_CLOEXEC); + if (fd < 0) + return fd; + + usage = dma_resv_usage_rw(arg.flags & DMA_BUF_SYNC_WRITE); + ret = dma_resv_get_singleton(dmabuf->resv, usage, &fence); + if (ret) + goto err_put_fd; + + if (!fence) + fence = dma_fence_get_stub(); + + sync_file = sync_file_create(fence); + + dma_fence_put(fence); + + if (!sync_file) { + ret = -ENOMEM; + goto err_put_fd; + } + + arg.fd = fd; + if (copy_to_user(user_data, &arg, sizeof(arg))) { + ret = -EFAULT; + goto err_put_file; + } + + fd_install(fd, sync_file->file); + + return 0; + +err_put_file: + fput(sync_file->file); +err_put_fd: + put_unused_fd(fd); + return ret; +} +#endif + static long dma_buf_ioctl(struct file *file, unsigned int cmd, unsigned long arg) { @@ -369,6 +431,11 @@ static long dma_buf_ioctl(struct file *file, case DMA_BUF_SET_NAME_B: return dma_buf_set_name(dmabuf, (const char __user *)arg); +#if IS_ENABLED(CONFIG_SYNC_FILE) + case DMA_BUF_IOCTL_EXPORT_SYNC_FILE: + return dma_buf_export_sync_file(dmabuf, (void __user *)arg); +#endif + default: return -ENOTTY; } diff --git a/include/uapi/linux/dma-buf.h b/include/uapi/linux/dma-buf.h index 8e4a2ca0bcbf..46f1e3e98b02 100644 --- a/include/uapi/linux/dma-buf.h +++ b/include/uapi/linux/dma-buf.h @@ -85,6 +85,40 @@ struct dma_buf_sync { #define DMA_BUF_NAME_LEN 32 +/** + * struct dma_buf_export_sync_file - Get a sync_file from a dma-buf + * + * Userspace can perform a DMA_BUF_IOCTL_EXPORT_SYNC_FILE to retrieve the + * current set of fences on a dma-buf file descriptor as a sync_file. CPU + * waits via poll() or other driver-specific mechanisms typically wait on + * whatever fences are on the dma-buf at the time the wait begins. This + * is similar except that it takes a snapshot of the current fences on the + * dma-buf for waiting later instead of waiting immediately. This is + * useful for modern graphics APIs such as Vulkan which assume an explicit + * synchronization model but still need to inter-operate with dma-buf. + */ +struct dma_buf_export_sync_file { + /** + * @flags: Read/write flags + * + * Must be DMA_BUF_SYNC_READ, DMA_BUF_SYNC_WRITE, or both. + * + * If DMA_BUF_SYNC_READ is set and DMA_BUF_SYNC_WRITE is not set, + * the returned sync file waits on any writers of the dma-buf to + * complete. Waiting on the returned sync file is equivalent to + * poll() with POLLIN. + * + * If DMA_BUF_SYNC_WRITE is set, the returned sync file waits on + * any users of the dma-buf (read or write) to complete. Waiting + * on the returned sync file is equivalent to poll() with POLLOUT. + * If both DMA_BUF_SYNC_WRITE and DMA_BUF_SYNC_READ are set, this + * is equivalent to just DMA_BUF_SYNC_WRITE. + */ + __u32 flags; + /** @fd: Returned sync file descriptor */ + __s32 fd; +}; + #define DMA_BUF_BASE 'b' #define DMA_BUF_IOCTL_SYNC _IOW(DMA_BUF_BASE, 0, struct dma_buf_sync) @@ -94,5 +128,6 @@ struct dma_buf_sync { #define DMA_BUF_SET_NAME _IOW(DMA_BUF_BASE, 1, const char *) #define DMA_BUF_SET_NAME_A _IOW(DMA_BUF_BASE, 1, u32) #define DMA_BUF_SET_NAME_B _IOW(DMA_BUF_BASE, 1, u64) +#define DMA_BUF_IOCTL_EXPORT_SYNC_FILE _IOWR(DMA_BUF_BASE, 2, struct dma_buf_export_sync_file) #endif From patchwork Fri May 6 18:02:16 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: Jason Ekstrand X-Patchwork-Id: 12842006 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 5FF79C433F5 for ; Sat, 7 May 2022 13:18:20 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 5B0221132BE; Sat, 7 May 2022 13:18:19 +0000 (UTC) Received: from mail-oi1-x22b.google.com (mail-oi1-x22b.google.com [IPv6:2607:f8b0:4864:20::22b]) by gabe.freedesktop.org (Postfix) with ESMTPS id 854D910EFA8 for ; Fri, 6 May 2022 18:02:23 +0000 (UTC) Received: by mail-oi1-x22b.google.com with SMTP id e189so8275212oia.8 for ; Fri, 06 May 2022 11:02:23 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=jlekstrand-net.20210112.gappssmtp.com; s=20210112; h=from:to:cc:subject:date:message-id:in-reply-to:references :mime-version:content-transfer-encoding; bh=1VQkoK/Xz58zI7Vgq0M9qXohq3zBglD3BOlY+KmjbuQ=; b=GyqH6CpxTZpWoT2/Brw+j2DlBYzcHVHV/R1m9XZ0mhBlXME9wRompiO+0Kn3rJeAtO xEtrjIRDphumD2WahjswF3HwwXfJ/Ozr+nu8bDiPt2ex71mJg9NpH1vTD8PKP3LKZN73 RnPH9M+qXDbqggvRqKRt5Uvl1ACV83b1MdkaP50sEURWc4yGvmTz1g9ORHimfeHqPDSV oM+15LOPVilsHF05WE2QNgwvbgij5sv+NBv4Y5u4SH/cWlwLowgCCZ87ekGZb4A95hvf 4ask1wqjURjWV/hPe00swrjX6p3PCRuVy9B+fQv59W0picNVOzWHh3Fz0LEZ2ZXa/TJX uByw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=1VQkoK/Xz58zI7Vgq0M9qXohq3zBglD3BOlY+KmjbuQ=; b=II6vtDj50p2SeMDqOd26ziGLtGlLS+i1uvdlQn6J/ETsefOGKHQXpQ8yok+pVmGHjb sUYZZa0AmyckWRW2bbCWjB/NWpyTBsAjTYXSo9BqKzPva2eqbL/ilRhyFNmRE6Ke4jXj bblJq/rcjB6baEj/ZV1Xy5Hzi712vYc6/D1JbNachlw4urHIl+s0H1gb21k588KJNlby cNoViiIf37wOcZEWS5Y0iFJFCDZc39FZ/aelZzOgIcxDpayRt+Q4PkEUzPS0J5VhrQnN mXLdxaLGmIO5imcfODS8/yQNEuT0bbXYcQkb+dBGwiQL5FHyaQ6DezAbKpHPvZnIffRy RA0Q== X-Gm-Message-State: AOAM531WN3sGdKy3DdJa59kCGXGalTW+qIFR0tkL0dR1Spc3JvB1THMP 4yFH+gjKMcr3FVBW5HrDO7jToLKBTijhyQ== X-Google-Smtp-Source: ABdhPJwi1cJ8uCdtVTee+Ixh++tSTRw3h5+GGect6Tm2VIugpg1ZW61hxdPEXke4MoRoi18VvBs6Sg== X-Received: by 2002:aca:428a:0:b0:326:4b9d:7272 with SMTP id p132-20020aca428a000000b003264b9d7272mr5453471oia.30.1651860142406; Fri, 06 May 2022 11:02:22 -0700 (PDT) Received: from animal.lan (2603-8080-2102-63d7-a603-c311-740a-6dbf.res6.spectrum.com. [2603:8080:2102:63d7:a603:c311:740a:6dbf]) by smtp.gmail.com with ESMTPSA id a32-20020a9d2623000000b006060322123csm1840998otb.12.2022.05.06.11.02.21 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 06 May 2022 11:02:21 -0700 (PDT) From: Jason Ekstrand To: dri-devel@lists.freedesktop.org Subject: [PATCH 2/2] dma-buf: Add an API for importing sync files (v9) Date: Fri, 6 May 2022 13:02:16 -0500 Message-Id: <20220506180216.2095060-3-jason@jlekstrand.net> X-Mailer: git-send-email 2.36.0 In-Reply-To: <20220506180216.2095060-1-jason@jlekstrand.net> References: <20220506180216.2095060-1-jason@jlekstrand.net> MIME-Version: 1.0 X-Mailman-Approved-At: Sat, 07 May 2022 13:18:19 +0000 X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Jason Ekstrand , =?utf-8?q?Christian_K?= =?utf-8?q?=C3=B6nig?= , Jason Ekstrand , Jason Ekstrand , Daniel Vetter , Sumit Semwal Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" This patch is analogous to the previous sync file export patch in that it allows you to import a sync_file into a dma-buf. Unlike the previous patch, however, this does add genuinely new functionality to dma-buf. Without this, the only way to attach a sync_file to a dma-buf is to submit a batch to your driver of choice which waits on the sync_file and claims to write to the dma-buf. Even if said batch is a no-op, a submit is typically way more overhead than just attaching a fence. A submit may also imply extra synchronization with other work because it happens on a hardware queue. In the Vulkan world, this is useful for dealing with the out-fence from vkQueuePresent. Current Linux window-systems (X11, Wayland, etc.) all rely on dma-buf implicit sync. Since Vulkan is an explicit sync API, we get a set of fences (VkSemaphores) in vkQueuePresent and have to stash those as an exclusive (write) fence on the dma-buf. We handle it in Mesa today with the above mentioned dummy submit trick. This ioctl would allow us to set it directly without the dummy submit. This may also open up possibilities for GPU drivers to move away from implicit sync for their kernel driver uAPI and instead provide sync files and rely on dma-buf import/export for communicating with other implicit sync clients. We make the explicit choice here to only allow setting RW fences which translates to an exclusive fence on the dma_resv. There's no use for read-only fences for communicating with other implicit sync userspace and any such attempts are likely to be racy at best. When we got to insert the RW fence, the actual fence we set as the new exclusive fence is a combination of the sync_file provided by the user and all the other fences on the dma_resv. This ensures that the newly added exclusive fence will never signal before the old one would have and ensures that we don't break any dma_resv contracts. We require userspace to specify RW in the flags for symmetry with the export ioctl and in case we ever want to support read fences in the future. There is one downside here that's worth documenting: If two clients writing to the same dma-buf using this API race with each other, their actions on the dma-buf may happen in parallel or in an undefined order. Both with and without this API, the pattern is the same: Collect all the fences on dma-buf, submit work which depends on said fences, and then set a new exclusive (write) fence on the dma-buf which depends on said work. The difference is that, when it's all handled by the GPU driver's submit ioctl, the three operations happen atomically under the dma_resv lock. If two userspace submits race, one will happen before the other. You aren't guaranteed which but you are guaranteed that they're strictly ordered. If userspace manages the fences itself, then these three operations happen separately and the two render operations may happen genuinely in parallel or get interleaved. However, this is a case of userspace racing with itself. As long as we ensure userspace can't back the kernel into a corner, it should be fine. v2 (Jason Ekstrand): - Use a wrapper dma_fence_array of all fences including the new one when importing an exclusive fence. v3 (Jason Ekstrand): - Lock around setting shared fences as well as exclusive - Mark SIGNAL_SYNC_FILE as a read-write ioctl. - Initialize ret to 0 in dma_buf_wait_sync_file v4 (Jason Ekstrand): - Use the new dma_resv_get_singleton helper v5 (Jason Ekstrand): - Rename the IOCTLs to import/export rather than wait/signal - Drop the WRITE flag and always get/set the exclusive fence v6 (Jason Ekstrand): - Split import and export into separate patches - New commit message v7 (Daniel Vetter): - Fix the uapi header to use the right struct in the ioctl - Use a separate dma_buf_import_sync_file struct - Add kerneldoc for dma_buf_import_sync_file v8 (Jason Ekstrand): - Rebase on Christian König's fence rework v9 (Daniel Vetter): - Fix -EINVAL checks for the flags parameter - Add documentation about read/write fences - Add documentation about the expected usage of import/export and specifically call out the possible userspace race. Signed-off-by: Jason Ekstrand Signed-off-by: Jason Ekstrand Signed-off-by: Jason Ekstrand Cc: Christian König Cc: Daniel Vetter Cc: Sumit Semwal Cc: Maarten Lankhorst --- drivers/dma-buf/dma-buf.c | 39 ++++++++++++++++++++++++++++ include/uapi/linux/dma-buf.h | 49 ++++++++++++++++++++++++++++++++++++ 2 files changed, 88 insertions(+) diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c index 6ff54f7e6119..f23f1482eb38 100644 --- a/drivers/dma-buf/dma-buf.c +++ b/drivers/dma-buf/dma-buf.c @@ -386,6 +386,43 @@ static long dma_buf_export_sync_file(struct dma_buf *dmabuf, put_unused_fd(fd); return ret; } + +static long dma_buf_import_sync_file(struct dma_buf *dmabuf, + const void __user *user_data) +{ + struct dma_buf_import_sync_file arg; + struct dma_fence *fence; + enum dma_resv_usage usage; + int ret = 0; + + if (copy_from_user(&arg, user_data, sizeof(arg))) + return -EFAULT; + + if (arg.flags & ~DMA_BUF_SYNC_RW) + return -EINVAL; + + if ((arg.flags & DMA_BUF_SYNC_RW) == 0) + return -EINVAL; + + fence = sync_file_get_fence(arg.fd); + if (!fence) + return -EINVAL; + + usage = (arg.flags & DMA_BUF_SYNC_WRITE) ? DMA_RESV_USAGE_WRITE : + DMA_RESV_USAGE_READ; + + dma_resv_lock(dmabuf->resv, NULL); + + ret = dma_resv_reserve_fences(dmabuf->resv, 1); + if (!ret) + dma_resv_add_fence(dmabuf->resv, fence, usage); + + dma_resv_unlock(dmabuf->resv); + + dma_fence_put(fence); + + return ret; +} #endif static long dma_buf_ioctl(struct file *file, @@ -434,6 +471,8 @@ static long dma_buf_ioctl(struct file *file, #if IS_ENABLED(CONFIG_SYNC_FILE) case DMA_BUF_IOCTL_EXPORT_SYNC_FILE: return dma_buf_export_sync_file(dmabuf, (void __user *)arg); + case DMA_BUF_IOCTL_IMPORT_SYNC_FILE: + return dma_buf_import_sync_file(dmabuf, (const void __user *)arg); #endif default: diff --git a/include/uapi/linux/dma-buf.h b/include/uapi/linux/dma-buf.h index 46f1e3e98b02..70e213a0d7d9 100644 --- a/include/uapi/linux/dma-buf.h +++ b/include/uapi/linux/dma-buf.h @@ -96,6 +96,24 @@ struct dma_buf_sync { * dma-buf for waiting later instead of waiting immediately. This is * useful for modern graphics APIs such as Vulkan which assume an explicit * synchronization model but still need to inter-operate with dma-buf. + * + * The intended usage pattern is the following: + * + * 1. Export a sync_file with flags corresponding to the expected GPU usage + * via DMA_BUF_IOCTL_EXPORT_SYNC_FILE. + * + * 2. Submit rendering work which uses the dma-buf. The work should wait on + * the exported sync file before rendering and produce another sync_file + * when complete. + * + * 3. Import the rendering-complete sync_file into the dma-buf with flags + * corresponding to the GPU usage via DMA_BUF_IOCTL_EXPORT_SYNC_FILE. + * + * Unlike doing implicit synchronization via a GPU kernel driver's exec ioctl, + * the above is not a single atomic operation. If userspace wants to ensure + * ordering via these fences, it is the respnosibility of userspace to use + * locks or other mechanisms to ensure that no other context adds fences or + * submits work between steps 1 and 3 above. */ struct dma_buf_export_sync_file { /** @@ -119,6 +137,36 @@ struct dma_buf_export_sync_file { __s32 fd; }; +/** + * struct dma_buf_import_sync_file - Insert a sync_file into a dma-buf + * + * Userspace can perform a DMA_BUF_IOCTL_IMPORT_SYNC_FILE to insert a + * sync_file into a dma-buf for the purposes of implicit synchronization + * with other dma-buf consumers. This allows clients using explicitly + * synchronized APIs such as Vulkan to inter-op with dma-buf consumers + * which expect implicit synchronization such as OpenGL or most media + * drivers/video. + */ +struct dma_buf_import_sync_file { + /** + * @flags: Read/write flags + * + * Must be DMA_BUF_SYNC_READ, DMA_BUF_SYNC_WRITE, or both. + * + * If DMA_BUF_SYNC_READ is set and DMA_BUF_SYNC_WRITE is not set, + * this inserts the sync_file as a read-only fence. Any subsequent + * implicitly synchronized writes to this dma-buf will wait on this + * fence but reads will not. + * + * If DMA_BUF_SYNC_WRITE is set, this inserts the sync_file as a + * write fence. All subsequent implicitly synchronized access to + * this dma-buf will wait on this fence. + */ + __u32 flags; + /** @fd: Sync file descriptor */ + __s32 fd; +}; + #define DMA_BUF_BASE 'b' #define DMA_BUF_IOCTL_SYNC _IOW(DMA_BUF_BASE, 0, struct dma_buf_sync) @@ -129,5 +177,6 @@ struct dma_buf_export_sync_file { #define DMA_BUF_SET_NAME_A _IOW(DMA_BUF_BASE, 1, u32) #define DMA_BUF_SET_NAME_B _IOW(DMA_BUF_BASE, 1, u64) #define DMA_BUF_IOCTL_EXPORT_SYNC_FILE _IOWR(DMA_BUF_BASE, 2, struct dma_buf_export_sync_file) +#define DMA_BUF_IOCTL_IMPORT_SYNC_FILE _IOW(DMA_BUF_BASE, 3, struct dma_buf_import_sync_file) #endif