linux-kernel - Re: [PATCH 03/14] arm64: Add per-cpu infrastructure to call ARCH_WORKAROUND_2

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Message-ID: <20180524111405.won7dozpt7gq5xda@lakrids.cambridge.arm.com>
Date:   Thu, 24 May 2018 12:14:05 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     Marc Zyngier <marc.zyngier@....com>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        kvmarm@...ts.cs.columbia.edu, Kees Cook <keescook@...omium.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Christoffer Dall <christoffer.dall@....com>,
        Andy Lutomirski <luto@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 03/14] arm64: Add per-cpu infrastructure to call
 ARCH_WORKAROUND_2

On Tue, May 22, 2018 at 04:06:37PM +0100, Marc Zyngier wrote:
> In a heterogeneous system, we can end up with both affected and
> unaffected CPUs. Let's check their status before calling into the
> firmware.
> 
> Signed-off-by: Marc Zyngier <marc.zyngier@....com>

Ah, I guess this may fix the issue I noted with the prior patch,
assuming we only set arm64_ssbd_callback_required for a CPU when the FW
supports the mitigation.

If so, if you fold this together with the prior patch:

Reviewed-by: Mark Rutland <mark.rutland@....com>

Thanks,
Mark.

> ---
>  arch/arm64/kernel/cpu_errata.c |  2 ++
>  arch/arm64/kernel/entry.S      | 11 +++++++----
>  2 files changed, 9 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c
> index 46b3aafb631a..0288d6cf560e 100644
> --- a/arch/arm64/kernel/cpu_errata.c
> +++ b/arch/arm64/kernel/cpu_errata.c
> @@ -233,6 +233,8 @@ enable_smccc_arch_workaround_1(const struct arm64_cpu_capabilities *entry)
>  #endif	/* CONFIG_HARDEN_BRANCH_PREDICTOR */
>  
>  #ifdef CONFIG_ARM64_SSBD
> +DEFINE_PER_CPU_READ_MOSTLY(u64, arm64_ssbd_callback_required);
> +
>  void __init arm64_update_smccc_conduit(struct alt_instr *alt,
>  				       __le32 *origptr, __le32 *updptr,
>  				       int nr_inst)
> diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
> index f33e6aed3037..29ad672a6abd 100644
> --- a/arch/arm64/kernel/entry.S
> +++ b/arch/arm64/kernel/entry.S
> @@ -140,8 +140,10 @@ alternative_else_nop_endif
>  
>  	// This macro corrupts x0-x3. It is the caller's duty
>  	// to save/restore them if required.
> -	.macro	apply_ssbd, state
> +	.macro	apply_ssbd, state, targ, tmp1, tmp2
>  #ifdef CONFIG_ARM64_SSBD
> +	ldr_this_cpu	\tmp2, arm64_ssbd_callback_required, \tmp1
> +	cbz	\tmp2, \targ
>  	mov	w0, #ARM_SMCCC_ARCH_WORKAROUND_2
>  	mov	w1, #\state
>  alternative_cb	arm64_update_smccc_conduit
> @@ -176,12 +178,13 @@ alternative_cb_end
>  	ldr	x19, [tsk, #TSK_TI_FLAGS]	// since we can unmask debug
>  	disable_step_tsk x19, x20		// exceptions when scheduling.
>  
> -	apply_ssbd 1
> +	apply_ssbd 1, 1f, x22, x23
>  
>  #ifdef CONFIG_ARM64_SSBD
>  	ldp	x0, x1, [sp, #16 * 0]
>  	ldp	x2, x3, [sp, #16 * 1]
>  #endif
> +1:
>  
>  	mov	x29, xzr			// fp pointed to user-space
>  	.else
> @@ -323,8 +326,8 @@ alternative_if ARM64_WORKAROUND_845719
>  alternative_else_nop_endif
>  #endif
>  3:
> -	apply_ssbd 0
> -
> +	apply_ssbd 0, 5f, x0, x1
> +5:
>  	.endif
>  
>  	msr	elr_el1, x21			// set up the return data
> -- 
> 2.14.2
> 
> 
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel@...ts.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

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