This is a note to let you know that I've just added the patch titled

powerpc/vas: Don't set uses_vas for kernel windows

to the 4.15-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...

The filename of the patch is: powerpc-vas-don-t-set-uses_vas-for-kernel-windows.patch and it can be found in the queue-4.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.

From b00b62898631b756c3e123542bbb0487aa343dd9 Mon Sep 17 00:00:00 2001

From: Nicholas Piggin npiggin@gmail.com Date: Thu, 8 Feb 2018 19:18:38 +1000 Subject: powerpc/vas: Don't set uses_vas for kernel windows

From: Nicholas Piggin npiggin@gmail.com

commit b00b62898631b756c3e123542bbb0487aa343dd9 upstream.

cp_abort is only required for user windows, because kernel context must not be preempted between a copy/paste pair.

Without this patch, the init task gets used_vas set when it runs the nx842_powernv_init initcall, which opens windows for kernel usage.

used_vas is then never cleared anywhere, so it gets propagated into all other tasks. It's a property of the address space, so it should really be cleared when a new mm is created (or in dup_mmap if the mmaps are marked as VM_DONTCOPY). For now we seem to have no such driver, so leave that for another patch.

Fixes: 6c8e6bb2a52d ("powerpc/vas: Add support for user receive window") Cc: stable@vger.kernel.org # v4.15+ Signed-off-by: Nicholas Piggin npiggin@gmail.com Reviewed-by: Sukadev Bhattiprolu sukadev@linux.vnet.ibm.com Signed-off-by: Michael Ellerman mpe@ellerman.id.au Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org

--- arch/powerpc/platforms/powernv/vas-window.c | 16 ++++++++-------- 1 file changed, 8 insertions(+), 8 deletions(-)

--- a/arch/powerpc/platforms/powernv/vas-window.c +++ b/arch/powerpc/platforms/powernv/vas-window.c @@ -1063,16 +1063,16 @@ struct vas_window *vas_tx_win_open(int v rc = PTR_ERR(txwin->paste_kaddr); goto free_window; } + } else { + /* + * A user mapping must ensure that context switch issues + * CP_ABORT for this thread. + */ + rc = set_thread_uses_vas(); + if (rc) + goto free_window; }

- /* - * Now that we have a send window, ensure context switch issues - * CP_ABORT for this thread. - */ - rc = -EINVAL; - if (set_thread_uses_vas() < 0) - goto free_window; - set_vinst_win(vinst, txwin);

return txwin;

Patches currently in stable-queue which might be from npiggin@gmail.com are

queue-4.15/powerpc-vas-don-t-set-uses_vas-for-kernel-windows.patch