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 1075f90fdd8ca5be5cfe9a2e3d24ea174bd63a28..2797bc2c8c6a88ec4687eefbdfaf558d8fa761e9 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 29ad672a6abdf52549bf80257394245366781abd..e6f6e2339b22f36cc9a03313bc2e77df07a15be0 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