[PATCH] xtensa: don't clear cpenable unconditionally on release

[PATCH] xtensa: don't clear cpenable unconditionally on release

[Max Filippov]

fast_coprocessor exception handler expects that the coprocessor owner
task never gets the "coprocessor disabled" exception for a coprocessor
that is marked as enabled in the thread_info::cpenable. If that happens
it will reload potentially outdated context from the thread_info
structure into the coprocessor registers.
Only call coprocessor_clear_cpenable from the coprocessor_release_all
if the latter is called for the current task.

Cc: stable@vger.kernel.org
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
---
 arch/xtensa/kernel/process.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/xtensa/kernel/process.c b/arch/xtensa/kernel/process.c
index 3fa0c440f664..6c7c80106f60 100644
--- a/arch/xtensa/kernel/process.c
+++ b/arch/xtensa/kernel/process.c
@@ -87,7 +87,8 @@ void coprocessor_release_all(struct thread_info *ti)
 	}
 
 	ti->cpenable = cpenable;
-	coprocessor_clear_cpenable();
+	if (ti == current_thread_info())
+		coprocessor_clear_cpenable();
 
 	preempt_enable();
 }
-- 
2.11.0

Re: [PATCH] xtensa: don't clear cpenable unconditionally on release

[Max Filippov]

On Mon, Nov 26, 2018 at 4:47 PM Max Filippov <jcmvbkbc@gmail.com> wrote:
>
> fast_coprocessor exception handler expects that the coprocessor owner
> task never gets the "coprocessor disabled" exception for a coprocessor
> that is marked as enabled in the thread_info::cpenable. If that happens
> it will reload potentially outdated context from the thread_info
> structure into the coprocessor registers.

After looking at it some more I see that the above is not true. It will
flush current coprocessor context to the thread_info and then load it
back from there. No correctness issue, but some extra work that
can be avoided.

-- 
Thanks.
-- Max