Hi,
On 13.07.26 11:12, Christian König wrote:
On 7/11/26 16:48, Robert Mader wrote:
As udmabuf increasingly enjoys popularity - being used in projects like
libcamera, Gstreamer, Mesa and KWin - users more frequently encounter
cases where the current default size limit of 64MB is too low. Examples
include allocating video buffers at a 8K resolution - and even 4K is
affected when using non-subsampled video formats or high bit depths.
While the limit can already be changed via the kernel command line,
exposing it as a kernel config makes that easier and more discoverable
for distros. Thus let's do that.
Well config options are usually only useful if the value can't be changed on
runtime through a module parameter, but that is clearly not the case here.
On the other hand I do see your problem. I would just vote to disable the limit
by default, there is nothing preventing userspace from allocating multiple
uDMA-bufs so it doesn't seem to prevent any security issue or similar.
I fully agree and would prefer that as well. If there is no resistance /
concerns from anybody I'll send a corresponding patch at the end of the
week.
Thanks,
Robert
Regards,
Christian.
Signed-off-by: Robert Mader <[email protected]>
---
drivers/dma-buf/Kconfig | 6 ++++++
drivers/dma-buf/udmabuf.c | 4 ++++
2 files changed, 10 insertions(+)
diff --git a/drivers/dma-buf/Kconfig b/drivers/dma-buf/Kconfig
index 7efc0f0d0712..35f0779cdc80 100644
--- a/drivers/dma-buf/Kconfig
+++ b/drivers/dma-buf/Kconfig
@@ -40,6 +40,12 @@ config UDMABUF
A driver to let userspace turn memfd regions into dma-bufs.
Qemu can use this to create host dmabufs for guest framebuffers.
+config UDMABUF_SIZE_LIMIT_MBYTES
+ int "Size limit in Mega Bytes"
+ default 64
+ help
+ Maximum size of a udmabuf, in megabytes. Default is 64.
+
config DMABUF_DEBUG
bool "DMA-BUF debug checks"
depends on DMA_SHARED_BUFFER
diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c
index bced421c0d65..a83153326362 100644
--- a/drivers/dma-buf/udmabuf.c
+++ b/drivers/dma-buf/udmabuf.c
@@ -20,7 +20,11 @@ static int list_limit = 1024;
module_param(list_limit, int, 0644);
MODULE_PARM_DESC(list_limit, "udmabuf_create_list->count limit. Default is
1024.");
+#ifdef CONFIG_UDMABUF_SIZE_LIMIT_MBYTES
+static int size_limit_mb = CONFIG_UDMABUF_SIZE_LIMIT_MBYTES;
+#else
static int size_limit_mb = 64;
+#endif
module_param(size_limit_mb, int, 0644);
MODULE_PARM_DESC(size_limit_mb, "Max size of a dmabuf, in megabytes. Default is
64.");
--
2.55.0
