Date:   Tue, 14 Apr 2020 15:46:27 +0200
From:   Ørjan Eide <orjan.eide@....com>
To:     unlisted-recipients:; (no To-header on input)
CC:     <orjan.eide@....com>, <anders.pedersen@....com>,
        <john.stultz@...aro.org>, Laura Abbott <labbott@...hat.com>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Arve Hjønnevåg <arve@...roid.com>,
        Todd Kjos <tkjos@...roid.com>,
        Martijn Coenen <maco@...roid.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Christian Brauner <christian@...uner.io>,
        "Daniel Vetter" <daniel.vetter@...ll.ch>,
        "Darren Hart (VMware)" <dvhart@...radead.org>,
        Lecopzer Chen <lecopzer.chen@...iatek.com>,
        "Arnd Bergmann" <arnd@...db.de>, <devel@...verdev.osuosl.org>,
        <dri-devel@...ts.freedesktop.org>,
        <linaro-mm-sig@...ts.linaro.org>, <linux-kernel@...r.kernel.org>,
        <linux-media@...r.kernel.org>
Subject: [PATCH] staging: android: ion: Skip sync if not mapped

Only sync the sg-list of an Ion dma-buf attachment when the attachment
is actually mapped on the device.

dma-bufs may be synced at any time. It can be reached from user space
via DMA_BUF_IOCTL_SYNC, so there are no guarantees from callers on when
syncs may be attempted, and dma_buf_end_cpu_access() and
dma_buf_begin_cpu_access() may not be paired.

Since the sg_list's dma_address isn't set up until the buffer is used
on the device, and dma_map_sg() is called on it, the dma_address will be
NULL if sync is attempted on the dma-buf before it's mapped on a device.

Before v5.0 (commit 55897af63091 ("dma-direct: merge swiotlb_dma_ops
into the dma_direct code")) this was a problem as the dma-api (at least
the swiotlb_dma_ops on arm64) would use the potentially invalid
dma_address. How that failed depended on how the device handled physical
address 0. If 0 was a valid address to physical ram, that page would get
flushed a lot, while the actual pages in the buffer would not get synced
correctly. While if 0 is an invalid physical address it may cause a
fault and trigger a crash.

In v5.0 this was incidentally fixed by commit 55897af63091 ("dma-direct:
merge swiotlb_dma_ops into the dma_direct code"), as this moved the
dma-api to use the page pointer in the sg_list, and (for Ion buffers at
least) this will always be valid if the sg_list exists at all.

But, this issue is re-introduced in v5.3 with
commit 449fa54d6815 ("dma-direct: correct the physical addr in
dma_direct_sync_sg_for_cpu/device") moves the dma-api back to the old
behaviour and picks the dma_address that may be invalid.

dma-buf core doesn't ensure that the buffer is mapped on the device, and
thus have a valid sg_list, before calling the exporter's
begin_cpu_access.

Signed-off-by: Ørjan Eide <orjan.eide@....com>
---
 drivers/staging/android/ion/ion.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

This seems to be part of a bigger issue where dma-buf exporters assume
that their dma-buf begin_cpu_access and end_cpu_access callbacks have a
certain guaranteed behavior, which isn't ensured by dma-buf core.

This patch fixes this in ion only, but it also needs to be fixed for
other exporters, either handled like this in each exporter, or in
dma-buf core before calling into the exporters.

diff --git a/drivers/staging/android/ion/ion.c b/drivers/staging/android/ion/ion.c
index 38b51eace4f9..7b752ba0cb6d 100644
--- a/drivers/staging/android/ion/ion.c
+++ b/drivers/staging/android/ion/ion.c
@@ -173,6 +173,7 @@ struct ion_dma_buf_attachment {
        struct device *dev;
        struct sg_table *table;
        struct list_head list;
+       bool mapped:1;
 };

 static int ion_dma_buf_attach(struct dma_buf *dmabuf,
@@ -195,6 +196,7 @@ static int ion_dma_buf_attach(struct dma_buf *dmabuf,
        a->table = table;
        a->dev = attachment->dev;
        INIT_LIST_HEAD(&a->list);
+       a->mapped = false;

        attachment->priv = a;

@@ -231,6 +233,8 @@ static struct sg_table *ion_map_dma_buf(struct dma_buf_attachment *attachment,
                        direction))
                return ERR_PTR(-ENOMEM);

+       a->mapped = true;
+
        return table;
 }

@@ -238,6 +242,10 @@ static void ion_unmap_dma_buf(struct dma_buf_attachment *attachment,
                              struct sg_table *table,
                              enum dma_data_direction direction)
 {
+       struct ion_dma_buf_attachment *a = attachment->priv;
+
+       a->mapped = false;
+
        dma_unmap_sg(attachment->dev, table->sgl, table->nents, direction);
 }

@@ -297,6 +305,8 @@ static int ion_dma_buf_begin_cpu_access(struct dma_buf *dmabuf,

        mutex_lock(&buffer->lock);
        list_for_each_entry(a, &buffer->attachments, list) {
+               if (!a->mapped)
+                       continue;
                dma_sync_sg_for_cpu(a->dev, a->table->sgl, a->table->nents,
                                    direction);
        }
@@ -320,6 +330,8 @@ static int ion_dma_buf_end_cpu_access(struct dma_buf *dmabuf,

        mutex_lock(&buffer->lock);
        list_for_each_entry(a, &buffer->attachments, list) {
+               if (!a->mapped)
+                       continue;
                dma_sync_sg_for_device(a->dev, a->table->sgl, a->table->nents,
                                       direction);
        }
--
2.17.1

IMPORTANT NOTICE: The contents of this email and any attachments are confidential and may also be privileged. If you are not the intended recipient, please notify the sender immediately and do not disclose the contents to any other person, use it for any purpose, or store or copy the information in any medium. Thank you.

Powered by blists - more mailing lists