linux-kernel - Re: [PATCH v2 12/20] arm64: capabilities: Change scope of VHE to Boot CPU feature

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Date:   Wed, 7 Feb 2018 10:39:03 +0000
From:   Dave Martin <Dave.Martin@....com>
To:     Suzuki K Poulose <suzuki.poulose@....com>
Cc:     linux-arm-kernel@...ts.infradead.org, mark.rutland@....com,
        ckadabi@...eaurora.org, ard.biesheuvel@...aro.org,
        marc.zyngier@....com, catalin.marinas@....com, will.deacon@....com,
        linux-kernel@...r.kernel.org, jnair@...iumnetworks.com,
        dave.martin@....com
Subject: Re: [PATCH v2 12/20] arm64: capabilities: Change scope of VHE to
 Boot CPU feature

On Wed, Jan 31, 2018 at 06:27:59PM +0000, Suzuki K Poulose wrote:
> We expect all CPUs to be running at the same EL inside the kernel
> with or without VHE enabled and we have strict checks to ensure
> that any mismatch triggers a kernel panic. If VHE is enabled,
> we use the feature based on the boot CPU and all other CPUs
> should follow. This makes it a perfect candidate for a cpability
> based on the boot CPU,  which should be matched by all the CPUs
> (both when is ON and OFF). This saves us some not-so-pretty
> hooks and special code, just for verifying the conflict.
> 
> Cc: Marc Zyngier <marc.zyngier@....com>
> Cc: Dave Martin <dave.martin@....com>
> Cc: Will Deacon <will.deacon@....com>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@....com>
> ---
>  arch/arm64/include/asm/cpufeature.h |  7 +++++++
>  arch/arm64/include/asm/virt.h       |  6 ------
>  arch/arm64/kernel/cpufeature.c      |  3 +--
>  arch/arm64/kernel/smp.c             | 38 -------------------------------------
>  4 files changed, 8 insertions(+), 46 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
> index 04161aac0f06..42292a0b93a4 100644
> --- a/arch/arm64/include/asm/cpufeature.h
> +++ b/arch/arm64/include/asm/cpufeature.h
> @@ -260,6 +260,13 @@ extern struct arm64_ftr_reg arm64_ftr_reg_ctrel0;
>  	(ARM64_CPUCAP_SCOPE_LOCAL_CPU		|	\
>  	 ARM64_CPUCAP_OPTIONAL_FOR_LATE_CPU)
>  
> +/*
> + * Critical CPU feature used early in the boot based on the boot CPU.
> + * The feature should be matched by all booting CPU (both miss and hit
> + * cases).
> + */
> +#define ARM64_CPUCAP_CRITICAL_BOOT_CPU_FEATURE ARM64_CPUCAP_SCOPE_BOOT_CPU
> +
>  struct arm64_cpu_capabilities {
>  	const char *desc;
>  	u16 capability;
> diff --git a/arch/arm64/include/asm/virt.h b/arch/arm64/include/asm/virt.h
> index c5f89442785c..9d1e24e030b3 100644
> --- a/arch/arm64/include/asm/virt.h
> +++ b/arch/arm64/include/asm/virt.h
> @@ -102,12 +102,6 @@ static inline bool has_vhe(void)
>  	return false;
>  }
>  
> -#ifdef CONFIG_ARM64_VHE
> -extern void verify_cpu_run_el(void);
> -#else
> -static inline void verify_cpu_run_el(void) {}
> -#endif
> -
>  #endif /* __ASSEMBLY__ */
>  
>  #endif /* ! __ASM__VIRT_H */
> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
> index 6d759f068de1..247d34ea6b5e 100644
> --- a/arch/arm64/kernel/cpufeature.c
> +++ b/arch/arm64/kernel/cpufeature.c
> @@ -982,7 +982,7 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
>  	{
>  		.desc = "Virtualization Host Extensions",
>  		.capability = ARM64_HAS_VIRT_HOST_EXTN,
> -		.type = ARM64_CPUCAP_SYSTEM_FEATURE,
> +		.type = ARM64_CPUCAP_CRITICAL_BOOT_CPU_FEATURE,
>  		.matches = runs_at_el2,
>  		.cpu_enable = cpu_copy_el2regs,
>  	},

Could this feature block now be #ifdef CONFIG_ARM64_VHE?

I don't think the lack of #ifdef breaks anything here though, because
in that case head.S drops down to EL1 runs_at_el2() returns false on
all CPUs.

> @@ -1322,7 +1322,6 @@ static bool verify_local_cpu_caps(u16 scope_mask)
>   */
>  static void check_early_cpu_features(void)
>  {
> -	verify_cpu_run_el();
>  	verify_cpu_asid_bits();
>  	/*
>  	 * Early features are used by the kernel already. If there
> diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
> index 5cef11450183..f3e2e3aec0b0 100644
> --- a/arch/arm64/kernel/smp.c
> +++ b/arch/arm64/kernel/smp.c
> @@ -85,43 +85,6 @@ enum ipi_msg_type {
>  	IPI_WAKEUP
>  };
>  
> -#ifdef CONFIG_ARM64_VHE
> -
> -/* Whether the boot CPU is running in HYP mode or not*/
> -static bool boot_cpu_hyp_mode;
> -
> -static inline void save_boot_cpu_run_el(void)
> -{
> -	boot_cpu_hyp_mode = is_kernel_in_hyp_mode();
> -}
> -
> -static inline bool is_boot_cpu_in_hyp_mode(void)
> -{
> -	return boot_cpu_hyp_mode;
> -}
> -
> -/*
> - * Verify that a secondary CPU is running the kernel at the same
> - * EL as that of the boot CPU.
> - */
> -void verify_cpu_run_el(void)
> -{
> -	bool in_el2 = is_kernel_in_hyp_mode();
> -	bool boot_cpu_el2 = is_boot_cpu_in_hyp_mode();
> -
> -	if (in_el2 ^ boot_cpu_el2) {
> -		pr_crit("CPU%d: mismatched Exception Level(EL%d) with boot CPU(EL%d)\n",
> -					smp_processor_id(),
> -					in_el2 ? 2 : 1,
> -					boot_cpu_el2 ? 2 : 1);
> -		cpu_panic_kernel();
> -	}
> -}
> -
> -#else
> -static inline void save_boot_cpu_run_el(void) {}
> -#endif
> -
>  #ifdef CONFIG_HOTPLUG_CPU
>  static int op_cpu_kill(unsigned int cpu);
>  #else
> @@ -447,7 +410,6 @@ void __init smp_prepare_boot_cpu(void)
>  	 */
>  	jump_label_init();
>  	cpuinfo_store_boot_cpu();
> -	save_boot_cpu_run_el();

Nice diffstat, assuming I didn't miss anything.

Cheers
---Dave