On Tue, May 22, 2018 at 04:06:41PM +0100, Marc Zyngier wrote:
> 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...
I guess in future we can magic up a more general asm static key if we
need them elsewhere.
> Signed-off-by: Marc Zyngier <marc.zyngier@xxxxxxx>
Reviewed-by: Mark Rutland <mark.rutland@xxxxxxx>
Mark.
> ---
> arch/arm64/kernel/cpu_errata.c | 14 ++++++++++++++
> arch/arm64/kernel/entry.S | 3 +++
> 2 files changed, 17 insertions(+)
>
> diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c
> index f1d4e75b0ddd..8f686f39b9c1 100644
> --- a/arch/arm64/kernel/cpu_errata.c
> +++ b/arch/arm64/kernel/cpu_errata.c
> @@ -283,6 +283,20 @@ 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_EL1_ENTRY)
> + *updptr = cpu_to_le32(aarch64_insn_gen_nop());
> +}
> +
> static void do_ssbd(bool state)
> {
> switch (psci_ops.conduit) {
> diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
> index 29ad672a6abd..e6f6e2339b22 100644
> --- 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
> --
> 2.14.2
>
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