powerpc/64: Fix booting large kernels with STRICT_KERNEL_RWX

[ Upstream commit 56c46bba9bbfe229b4472a5be313c44c5b714a39 ]

With STRICT_KERNEL_RWX enabled anything marked __init is placed at a 16M
boundary.  This is necessary so that it can be repurposed later with
different permissions.  However, in kernels with text larger than 16M,
this pushes early_setup past 32M, incapable of being reached by the
branch instruction.

Fix this by setting the CTR and branching there instead.

Fixes: 1e0fc9d1eb2b ("powerpc/Kconfig: Enable STRICT_KERNEL_RWX for some configs")
Signed-off-by: Russell Currey <ruscur@russell.cc>
[mpe: Fix it to work on BE by using DOTSYM()]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/arch/powerpc/kernel/head_64.S b/arch/powerpc/kernel/head_64.S
index 4898e94..9168a24 100644 (file)
--- a/arch/powerpc/kernel/head_64.S
+++ b/arch/powerpc/kernel/head_64.S
@@ -970,7 +970,9 @@ start_here_multiplatform:
 
        /* Restore parameters passed from prom_init/kexec */
        mr      r3,r31
-       bl      early_setup             /* also sets r13 and SPRG_PACA */
+       LOAD_REG_ADDR(r12, DOTSYM(early_setup))
+       mtctr   r12
+       bctrl           /* also sets r13 and SPRG_PACA */
 
        LOAD_REG_ADDR(r3, start_here_common)
        ld      r4,PACAKMSR(r13)