arm64: ssbd: Skip apply_ssbd if not using dynamic mitigation

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>

diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c
index 1075f90..2797bc2 100644 (file)
--- a/arch/arm64/kernel/cpu_errata.c
+++ b/arch/arm64/kernel/cpu_errata.c
@@ -289,6 +289,20 @@ 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 29ad672..e6f6e23 100644 (file)
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -142,6 +142,9 @@ 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