linux-kernel - Re: [PATCH v4 13/21] arm64: Allow ID_AA64MMFR1_EL1.VH to be overridden from the command line

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Date:   Sat, 23 Jan 2021 14:04:31 +0000
From:   Catalin Marinas <catalin.marinas@....com>
To:     Marc Zyngier <maz@...nel.org>
Cc:     linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        linux-kernel@...r.kernel.org, Will Deacon <will@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        David Brazdil <dbrazdil@...gle.com>,
        Alexandru Elisei <alexandru.elisei@....com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Jing Zhang <jingzhangos@...gle.com>,
        Ajay Patil <pajay@....qualcomm.com>,
        Prasad Sodagudi <psodagud@...eaurora.org>,
        Srinivas Ramana <sramana@...eaurora.org>,
        James Morse <james.morse@....com>,
        Julien Thierry <julien.thierry.kdev@...il.com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        kernel-team@...roid.com
Subject: Re: [PATCH v4 13/21] arm64: Allow ID_AA64MMFR1_EL1.VH to be
 overridden from the command line

On Mon, Jan 18, 2021 at 09:45:25AM +0000, Marc Zyngier wrote:
> diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
> index fe0130d6c0ff..80a5f423444e 100644
> --- a/arch/arm64/include/asm/cpufeature.h
> +++ b/arch/arm64/include/asm/cpufeature.h
> @@ -814,6 +814,9 @@ static inline unsigned int get_vmid_bits(u64 mmfr1)
>  	return 8;
>  }
>  
> +extern u64 id_aa64mmfr1_val;
> +extern u64 id_aa64mmfr1_mask;
> +
>  u32 get_kvm_ipa_limit(void);
>  void dump_cpu_features(void);
>  
> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
> index 48a011935d8c..5b9343d2e9f0 100644
> --- a/arch/arm64/kernel/cpufeature.c
> +++ b/arch/arm64/kernel/cpufeature.c
> @@ -555,6 +555,9 @@ static const struct arm64_ftr_bits ftr_raz[] = {
>  
>  #define ARM64_FTR_REG(id, table) ARM64_FTR_REG_OVERRIDE(id, table, NULL, NULL)
>  
> +u64 id_aa64mmfr1_val;
> +u64 id_aa64mmfr1_mask;
> +
>  static const struct __ftr_reg_entry {
>  	u32			sys_id;
>  	struct arm64_ftr_reg 	*reg;
> @@ -602,7 +605,8 @@ static const struct __ftr_reg_entry {
>  
>  	/* Op1 = 0, CRn = 0, CRm = 7 */
>  	ARM64_FTR_REG(SYS_ID_AA64MMFR0_EL1, ftr_id_aa64mmfr0),
> -	ARM64_FTR_REG(SYS_ID_AA64MMFR1_EL1, ftr_id_aa64mmfr1),
> +	ARM64_FTR_REG_OVERRIDE(SYS_ID_AA64MMFR1_EL1, ftr_id_aa64mmfr1,
> +			       &id_aa64mmfr1_val, &id_aa64mmfr1_mask),
>  	ARM64_FTR_REG(SYS_ID_AA64MMFR2_EL1, ftr_id_aa64mmfr2),
>  
>  	/* Op1 = 0, CRn = 1, CRm = 2 */
> diff --git a/arch/arm64/kernel/idreg-override.c b/arch/arm64/kernel/idreg-override.c
> index 392f93b67103..75d9845f489b 100644
> --- a/arch/arm64/kernel/idreg-override.c
> +++ b/arch/arm64/kernel/idreg-override.c
> @@ -10,6 +10,7 @@
>  #include <linux/libfdt.h>
>  
>  #include <asm/cacheflush.h>
> +#include <asm/cpufeature.h>
>  #include <asm/setup.h>
>  
>  struct reg_desc {
> @@ -22,7 +23,18 @@ struct reg_desc {
>  	} 			fields[];
>  };
>  
> +static const struct reg_desc mmfr1 __initdata = {
> +	.name		= "id_aa64mmfr1",
> +	.val		= &id_aa64mmfr1_val,
> +	.mask		= &id_aa64mmfr1_mask,
> +	.fields		= {
> +	        { "vh", ID_AA64MMFR1_VHE_SHIFT },
> +		{}
> +	},
> +};
> +
>  static const struct reg_desc * const regs[] __initdata = {
> +	&mmfr1,
>  };

I'm ok in principle with how all these link together. I wonder however
if we could skip the separate u64 variables and just have a struct
reg_override with val and mask u64 rather than pointers. The
ARM64_FTR_REG_OVERRIDE macro takes a pointer to this new struct
reg_override and can access val/mask directly. Some 'const' may need to
be dropped.

-- 
Catalin