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Subject[PATCH] usb: gadget: f_fs: try to fix AIO issue under ARM 64 bit TAGGED mode
Date
This issue was found when adbd trying to open functionfs with AIO mode.
Usually, we need to set "setprop sys.usb.ffs.aio_compat 0" to enable
adbd with AIO mode on Android.

When adbd is opening functionfs, it will try to read 24 bytes at the
fisrt read I/O control. If this reading has been failed, adbd will
try to send FUNCTIONFS_CLEAR_HALT to functionfs. When adbd is in AIO
mode, functionfs will be acted with asyncronized I/O path. After the
successful read transfer has been completed by gadget hardware, the
following series of functions will be called.
ffs_epfile_async_io_complete() -> ffs_user_copy_worker() ->
copy_to_iter() -> _copy_to_iter() -> copyout() ->
iterate_and_advance() -> iterate_iovec()

Adding debug trace to these functions, it has been found that in
copyout(), access_ok() will check if the user space address is valid
to write. However if CONFIG_ARM64_TAGGED_ADDR_ABI is enabled, adbd
always passes user space address start with "0x3C" to gdaget's AIO
blocks. This tagged address will cause access_ok() check always fail.
Which causes later calculation in iterate_iovec() turn zero.
Copyout() won't copy data to userspace since the length to be copied
"v.iov_len" will be zero. Finally leads ffs_copy_to_iter() always return
-EFAULT, causes adbd cannot open functionfs and send
FUNCTIONFS_CLEAR_HALT.

Signed-off-by: Macpaul Lin <macpaul.lin@mediatek.com>
---
drivers/usb/gadget/function/f_fs.c | 3 +++
1 file changed, 3 insertions(+)

diff --git a/drivers/usb/gadget/function/f_fs.c b/drivers/usb/gadget/function/f_fs.c
index ce1d023..b21541a 100644
--- a/drivers/usb/gadget/function/f_fs.c
+++ b/drivers/usb/gadget/function/f_fs.c
@@ -35,6 +35,7 @@
#include <linux/mmu_context.h>
#include <linux/poll.h>
#include <linux/eventfd.h>
+#include <linux/thread_info.h>

#include "u_fs.h"
#include "u_f.h"
@@ -826,6 +827,8 @@ static void ffs_user_copy_worker(struct work_struct *work)
if (io_data->read && ret > 0) {
mm_segment_t oldfs = get_fs();

+ if (IS_ENABLED(CONFIG_ARM64_TAGGED_ADDR_ABI))
+ set_thread_flag(TIF_TAGGED_ADDR);
set_fs(USER_DS);
use_mm(io_data->mm);
ret = ffs_copy_to_iter(io_data->buf, ret, &io_data->data);
--
1.7.9.5
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