From: Nathan Lynch nathanl@linux.ibm.com
[ 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@linux.ibm.com Fixes: 033ef338b6e0 ("powerpc: Merge rtas.c into arch/powerpc/kernel") Signed-off-by: Michael Ellerman mpe@ellerman.id.au Link: https://lore.kernel.org/r/20230125-b4-powerpc-rtas-queue-v3-6-26929c8cce78@l... Signed-off-by: Sasha Levin sashal@kernel.org --- arch/powerpc/kernel/rtas.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
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;