linux-kernel - Re: [PATCH v2 08/17] arm64: ssbd: Restore mitigation status on CPU resume

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Message-ID: <20180529133510.xopxpmxf7ypjeksc@lakrids.cambridge.arm.com>
Date:   Tue, 29 May 2018 14:35:13 +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, Will Deacon <will.deacon@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andy Lutomirski <luto@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Christoffer Dall <christoffer.dall@....com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Dominik Brodowski <linux@...inikbrodowski.net>,
        Julien Grall <julien.grall@....com>
Subject: Re: [PATCH v2 08/17] arm64: ssbd: Restore mitigation status on CPU
 resume

On Tue, May 29, 2018 at 01:11:12PM +0100, Marc Zyngier wrote:
> On a system where firmware can dynamically change the state of the
> mitigation, the CPU will always come up with the mitigation enabled,
> including when coming back from suspend.
> 
> If the user has requested "no mitigation" via a command line option,
> let's enforce it by calling into the firmware again to disable it.
> 
> Similarily, for a resume from hibernate, the mitigation could have
> been disabled by the boot kernel. Let's ensure that it is set
> back on in that case.
> 
> Signed-off-by: Marc Zyngier <marc.zyngier@....com>

With teh fixup in swsusp_arch_suspend(), this looks good to me. FWIW:

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

Mark.

> ---
>  arch/arm64/include/asm/cpufeature.h |  6 ++++++
>  arch/arm64/kernel/cpu_errata.c      |  2 +-
>  arch/arm64/kernel/hibernate.c       | 11 +++++++++++
>  arch/arm64/kernel/suspend.c         |  8 ++++++++
>  4 files changed, 26 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
> index b0fc3224ce8a..55bc1f073bfb 100644
> --- a/arch/arm64/include/asm/cpufeature.h
> +++ b/arch/arm64/include/asm/cpufeature.h
> @@ -553,6 +553,12 @@ static inline int arm64_get_ssbd_state(void)
>  #endif
>  }
>  
> +#ifdef CONFIG_ARM64_SSBD
> +void arm64_set_ssbd_mitigation(bool state);
> +#else
> +static inline void arm64_set_ssbd_mitigation(bool state) {}
> +#endif
> +
>  #endif /* __ASSEMBLY__ */
>  
>  #endif
> diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c
> index 2fef634e6953..2b9a31a6a16a 100644
> --- a/arch/arm64/kernel/cpu_errata.c
> +++ b/arch/arm64/kernel/cpu_errata.c
> @@ -303,7 +303,7 @@ void __init arm64_enable_wa2_handling(struct alt_instr *alt,
>  		*updptr = cpu_to_le32(aarch64_insn_gen_nop());
>  }
>  
> -static void arm64_set_ssbd_mitigation(bool state)
> +void arm64_set_ssbd_mitigation(bool state)
>  {
>  	switch (psci_ops.conduit) {
>  	case PSCI_CONDUIT_HVC:
> diff --git a/arch/arm64/kernel/hibernate.c b/arch/arm64/kernel/hibernate.c
> index 1ec5f28c39fc..6b2686d54411 100644
> --- a/arch/arm64/kernel/hibernate.c
> +++ b/arch/arm64/kernel/hibernate.c
> @@ -313,6 +313,17 @@ int swsusp_arch_suspend(void)
>  
>  		sleep_cpu = -EINVAL;
>  		__cpu_suspend_exit();
> +
> +		/*
> +		 * Just in case the boot kernel did turn the SSBD
> +		 * mitigation off behind our back, let's set the state
> +		 * to what we expect it to be.
> +		 */
> +		switch (arm64_get_ssbd_state()) {
> +		case ARM64_SSBD_FORCE_ENABLE:
> +		case ARM64_SSBD_KERNEL:
> +			arm64_set_ssbd_mitigation(true);
> +		}
>  	}
>  
>  	local_daif_restore(flags);
> diff --git a/arch/arm64/kernel/suspend.c b/arch/arm64/kernel/suspend.c
> index a307b9e13392..70c283368b64 100644
> --- a/arch/arm64/kernel/suspend.c
> +++ b/arch/arm64/kernel/suspend.c
> @@ -62,6 +62,14 @@ void notrace __cpu_suspend_exit(void)
>  	 */
>  	if (hw_breakpoint_restore)
>  		hw_breakpoint_restore(cpu);
> +
> +	/*
> +	 * On resume, firmware implementing dynamic mitigation will
> +	 * have turned the mitigation on. If the user has forcefully
> +	 * disabled it, make sure their wishes are obeyed.
> +	 */
> +	if (arm64_get_ssbd_state() == ARM64_SSBD_FORCE_DISABLE)
> +		arm64_set_ssbd_mitigation(false);
>  }
>  
>  /*
> -- 
> 2.14.2
>