arm64: ssbd: Skip apply_ssbd if not using dynamic mitigation

commit 986372c4367f46b34a3c0f6918d7fb95cbdf39d6 upstream.

In order to avoid checking arm64_ssbd_callback_required on each
kernel entry/exit even if no mitigation is required, let's
add yet another alternative that by default jumps over the mitigation,
and that gets nop'ed out if we're doing dynamic mitigation.

Think of it as a poor man's static key...

Reviewed-by: Julien Grall <julien.grall@arm.com>
Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c
index 4e9fa2a34b88460793ba6fce581da4fd2cae6a0a..9e0b311873ef92b068e92a8b6f612dbfbe1a01e6 100644 (file)
--- a/arch/arm64/kernel/cpu_errata.c
+++ b/arch/arm64/kernel/cpu_errata.c
@@ -244,6 +244,20 @@ void __init arm64_update_smccc_conduit(struct alt_instr *alt,
        *updptr = cpu_to_le32(insn);
 }
 
+void __init arm64_enable_wa2_handling(struct alt_instr *alt,
+                                     __le32 *origptr, __le32 *updptr,
+                                     int nr_inst)
+{
+       BUG_ON(nr_inst != 1);
+       /*
+        * Only allow mitigation on EL1 entry/exit and guest
+        * ARCH_WORKAROUND_2 handling if the SSBD state allows it to
+        * be flipped.
+        */
+       if (arm64_get_ssbd_state() == ARM64_SSBD_KERNEL)
+               *updptr = cpu_to_le32(aarch64_insn_gen_nop());
+}
+
 static void arm64_set_ssbd_mitigation(bool state)
 {
        switch (psci_ops.conduit) {

diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index 0f2510bd1ef9c2068fdb3c5b04c5e9796cf82c7a..75f1d9f051e89a67082a5ebf0279b266af623bd5 100644 (file)
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -100,6 +100,9 @@ alternative_else_nop_endif
        // to save/restore them if required.
        .macro  apply_ssbd, state, targ, tmp1, tmp2
 #ifdef CONFIG_ARM64_SSBD
+alternative_cb arm64_enable_wa2_handling
+       b       \targ
+alternative_cb_end
        ldr_this_cpu    \tmp2, arm64_ssbd_callback_required, \tmp1
        cbz     \tmp2, \targ
        mov     w0, #ARM_SMCCC_ARCH_WORKAROUND_2