[PATCH] arm64: cpufeature: Fix feature comparison for CTR_EL0.{CWG, ERG}

[PATCH] arm64: cpufeature: Fix feature comparison for CTR_EL0.{CWG, ERG}

[Will Deacon]

If CTR_EL0.{CWG,ERG} are 0b0000 then they must be interpreted to have
their architecturally maximum values, which defeats the use of
FTR_HIGHER_SAFE when sanitising CPU ID registers on heterogeneous
machines.

Introduce FTR_HIGHER_OR_ZERO_SAFE so that these fields effectively
saturate at zero.

Cc: Suzuki Poulose <suzuki.poulose@arm.com>
Fixes: 3c739b571084 ("arm64: Keep track of CPU feature registers")
Signed-off-by: Will Deacon <will@kernel.org>
---
 arch/arm64/include/asm/cpufeature.h | 7 ++++---
 arch/arm64/kernel/cpufeature.c      | 8 ++++++--
 2 files changed, 10 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
index 407e2bf23676..c96ffa4722d3 100644
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/arch/arm64/include/asm/cpufeature.h
@@ -35,9 +35,10 @@
  */
 
 enum ftr_type {
-	FTR_EXACT,	/* Use a predefined safe value */
-	FTR_LOWER_SAFE,	/* Smaller value is safe */
-	FTR_HIGHER_SAFE,/* Bigger value is safe */
+	FTR_EXACT,			/* Use a predefined safe value */
+	FTR_LOWER_SAFE,			/* Smaller value is safe */
+	FTR_HIGHER_SAFE,		/* Bigger value is safe */
+	FTR_HIGHER_OR_ZERO_SAFE,	/* Bigger value is safe, but 0 is biggest */
 };
 
 #define FTR_STRICT	true	/* SANITY check strict matching required */
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index f29f36a65175..d19d14ba9ae4 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -225,8 +225,8 @@ static const struct arm64_ftr_bits ftr_ctr[] = {
 	ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_EXACT, 31, 1, 1), /* RES1 */
 	ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_LOWER_SAFE, CTR_DIC_SHIFT, 1, 1),
 	ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_LOWER_SAFE, CTR_IDC_SHIFT, 1, 1),
-	ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_HIGHER_SAFE, CTR_CWG_SHIFT, 4, 0),
-	ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_HIGHER_SAFE, CTR_ERG_SHIFT, 4, 0),
+	ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_HIGHER_OR_ZERO_SAFE, CTR_CWG_SHIFT, 4, 0),
+	ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_HIGHER_OR_ZERO_SAFE, CTR_ERG_SHIFT, 4, 0),
 	ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_LOWER_SAFE, CTR_DMINLINE_SHIFT, 4, 1),
 	/*
 	 * Linux can handle differing I-cache policies. Userspace JITs will
@@ -468,6 +468,10 @@ static s64 arm64_ftr_safe_value(const struct arm64_ftr_bits *ftrp, s64 new,
 	case FTR_LOWER_SAFE:
 		ret = new < cur ? new : cur;
 		break;
+	case FTR_HIGHER_OR_ZERO_SAFE:
+		if (!cur || !new)
+			break;
+		/* Fallthrough */
 	case FTR_HIGHER_SAFE:
 		ret = new > cur ? new : cur;
 		break;
-- 
2.11.0


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Re: [PATCH] arm64: cpufeature: Fix feature comparison for CTR_EL0.{CWG,ERG}

[Suzuki K Poulose]

On 07/30/2019 03:40 PM, Will Deacon wrote:
> If CTR_EL0.{CWG,ERG} are 0b0000 then they must be interpreted to have
> their architecturally maximum values, which defeats the use of
> FTR_HIGHER_SAFE when sanitising CPU ID registers on heterogeneous
> machines.
> 
> Introduce FTR_HIGHER_OR_ZERO_SAFE so that these fields effectively
> saturate at zero.
> 
> Cc: Suzuki Poulose <suzuki.poulose@arm.com>
> Fixes: 3c739b571084 ("arm64: Keep track of CPU feature registers")
> Signed-off-by: Will Deacon <will@kernel.org>

Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>

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Re: [PATCH] arm64: cpufeature: Fix feature comparison for CTR_EL0.{CWG, ERG}

[Mark Rutland]

On Tue, Jul 30, 2019 at 03:40:20PM +0100, Will Deacon wrote:
> If CTR_EL0.{CWG,ERG} are 0b0000 then they must be interpreted to have
> their architecturally maximum values, which defeats the use of
> FTR_HIGHER_SAFE when sanitising CPU ID registers on heterogeneous
> machines.
> 
> Introduce FTR_HIGHER_OR_ZERO_SAFE so that these fields effectively
> saturate at zero.
> 
> Cc: Suzuki Poulose <suzuki.poulose@arm.com>
> Fixes: 3c739b571084 ("arm64: Keep track of CPU feature registers")
> Signed-off-by: Will Deacon <will@kernel.org>
> ---
>  arch/arm64/include/asm/cpufeature.h | 7 ++++---
>  arch/arm64/kernel/cpufeature.c      | 8 ++++++--
>  2 files changed, 10 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
> index 407e2bf23676..c96ffa4722d3 100644
> --- a/arch/arm64/include/asm/cpufeature.h
> +++ b/arch/arm64/include/asm/cpufeature.h
> @@ -35,9 +35,10 @@
>   */
>  
>  enum ftr_type {
> -	FTR_EXACT,	/* Use a predefined safe value */
> -	FTR_LOWER_SAFE,	/* Smaller value is safe */
> -	FTR_HIGHER_SAFE,/* Bigger value is safe */
> +	FTR_EXACT,			/* Use a predefined safe value */
> +	FTR_LOWER_SAFE,			/* Smaller value is safe */
> +	FTR_HIGHER_SAFE,		/* Bigger value is safe */
> +	FTR_HIGHER_OR_ZERO_SAFE,	/* Bigger value is safe, but 0 is biggest */
>  };

Does this mean we've disproved the FUTEX_MAX_LOOPS conjecture? ;)

FWIW:

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

Mark.

>  
>  #define FTR_STRICT	true	/* SANITY check strict matching required */
> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
> index f29f36a65175..d19d14ba9ae4 100644
> --- a/arch/arm64/kernel/cpufeature.c
> +++ b/arch/arm64/kernel/cpufeature.c
> @@ -225,8 +225,8 @@ static const struct arm64_ftr_bits ftr_ctr[] = {
>  	ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_EXACT, 31, 1, 1), /* RES1 */
>  	ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_LOWER_SAFE, CTR_DIC_SHIFT, 1, 1),
>  	ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_LOWER_SAFE, CTR_IDC_SHIFT, 1, 1),
> -	ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_HIGHER_SAFE, CTR_CWG_SHIFT, 4, 0),
> -	ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_HIGHER_SAFE, CTR_ERG_SHIFT, 4, 0),
> +	ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_HIGHER_OR_ZERO_SAFE, CTR_CWG_SHIFT, 4, 0),
> +	ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_HIGHER_OR_ZERO_SAFE, CTR_ERG_SHIFT, 4, 0),
>  	ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_LOWER_SAFE, CTR_DMINLINE_SHIFT, 4, 1),
>  	/*
>  	 * Linux can handle differing I-cache policies. Userspace JITs will
> @@ -468,6 +468,10 @@ static s64 arm64_ftr_safe_value(const struct arm64_ftr_bits *ftrp, s64 new,
>  	case FTR_LOWER_SAFE:
>  		ret = new < cur ? new : cur;
>  		break;
> +	case FTR_HIGHER_OR_ZERO_SAFE:
> +		if (!cur || !new)
> +			break;
> +		/* Fallthrough */
>  	case FTR_HIGHER_SAFE:
>  		ret = new > cur ? new : cur;
>  		break;
> -- 
> 2.11.0
> 
> 
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> linux-arm-kernel@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

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Re: [PATCH] arm64: cpufeature: Fix feature comparison for CTR_EL0.{CWG,ERG}

[Catalin Marinas]

On Tue, Jul 30, 2019 at 03:40:20PM +0100, Will Deacon wrote:
> If CTR_EL0.{CWG,ERG} are 0b0000 then they must be interpreted to have
> their architecturally maximum values, which defeats the use of
> FTR_HIGHER_SAFE when sanitising CPU ID registers on heterogeneous
> machines.
> 
> Introduce FTR_HIGHER_OR_ZERO_SAFE so that these fields effectively
> saturate at zero.
> 
> Cc: Suzuki Poulose <suzuki.poulose@arm.com>
> Fixes: 3c739b571084 ("arm64: Keep track of CPU feature registers")
> Signed-off-by: Will Deacon <will@kernel.org>

Queued for 5.3-rc3 (with a cc stable tag). Thanks.

-- 
Catalin

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