This is a note to let you know that I've just added the patch titled
powerpc/rtas: ensure 4KB alignment for rtas_data_buf
to the 4.19-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
powerpc-rtas-ensure-4kb-alignment-for-rtas_data_buf.patch
and it can be found in the queue-4.19 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 2e2d23af680231c7db1a15cce19e08f91223bfa3
Author: Nathan Lynch <nathanl@xxxxxxxxxxxxx>
Date: Fri Feb 10 12:41:54 2023 -0600
powerpc/rtas: ensure 4KB alignment for rtas_data_buf
[ Upstream commit 836b5b9fcc8e09cea7e8a59a070349a00e818308 ]
Some RTAS functions that have work area parameters impose alignment
requirements on the work area passed to them by the OS. Examples
include:
- ibm,configure-connector
- ibm,update-nodes
- ibm,update-properties
4KB is the greatest alignment required by PAPR for such
buffers. rtas_data_buf used to have a __page_aligned attribute in the
arch/ppc64 days, but that was changed to __cacheline_aligned for
unknown reasons by commit 033ef338b6e0 ("powerpc: Merge rtas.c into
arch/powerpc/kernel"). That works out to 128-byte alignment
on ppc64, which isn't right.
This was found by inspection and I'm not aware of any real problems
caused by this. Either current RTAS implementations don't enforce the
alignment constraints, or rtas_data_buf is always being placed at a
4KB boundary by accident (or both, perhaps).
Use __aligned(SZ_4K) to ensure the rtas_data_buf has alignment
appropriate for all users.
Signed-off-by: Nathan Lynch <nathanl@xxxxxxxxxxxxx>
Fixes: 033ef338b6e0 ("powerpc: Merge rtas.c into arch/powerpc/kernel")
Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20230125-b4-powerpc-rtas-queue-v3-6-26929c8cce78@xxxxxxxxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/arch/powerpc/kernel/rtas.c b/arch/powerpc/kernel/rtas.c
index 07d1ef762936d..7c7648e6f1c22 100644
--- a/arch/powerpc/kernel/rtas.c
+++ b/arch/powerpc/kernel/rtas.c
@@ -56,7 +56,7 @@ EXPORT_SYMBOL(rtas);
DEFINE_SPINLOCK(rtas_data_buf_lock);
EXPORT_SYMBOL_GPL(rtas_data_buf_lock);
-char rtas_data_buf[RTAS_DATA_BUF_SIZE] __cacheline_aligned;
+char rtas_data_buf[RTAS_DATA_BUF_SIZE] __aligned(SZ_4K);
EXPORT_SYMBOL_GPL(rtas_data_buf);
unsigned long rtas_rmo_buf;
