linux-kernel - Re: [PATCH] arm64: Check for errata before evaluating cpu features

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Message-ID: <20180725085604.GB4240@e103592.cambridge.arm.com>
Date:   Wed, 25 Jul 2018 09:56:04 +0100
From:   Dave Martin <Dave.Martin@....com>
To:     Suzuki K Poulose <suzuki.poulose@....com>
Cc:     Dirk Mueller <dmueller@...e.com>,
        linux-arm-kernel@...ts.infradead.org,
        Marc Zyngier <marc.zyngier@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        linux-kernel@...r.kernel.org, Alex Graf <agraf@...e.de>
Subject: Re: [PATCH] arm64: Check for errata before evaluating cpu features

On Wed, Jul 25, 2018 at 09:51:53AM +0100, Suzuki K Poulose wrote:
> On 07/25/2018 09:35 AM, Dirk Mueller wrote:
> >Since commit d3aec8a28be3b8 ("arm64: capabilities: Restrict KPTI
> >detection to boot-time CPUs") we rely on errata flags being already
> >populated during feature enumeration. The order of errata and
> >features was flipped as part of commit ed478b3f9e4a ("arm64:
> >capabilities: Group handling of features and errata workarounds").
> >
> >Return to the orginal order of errata and feature evaluation to
> >ensure errata flags are present during feature evaluation.
> >
> >Fixes: d3aec8a28be3b8 ("arm64: capabilities: Restrict KPTI
> >detection to boot-time CPUs")
> >CC: Suzuki K Poulose <suzuki.poulose@....com>
> >CC: Marc Zyngier <marc.zyngier@....com>
> >Signed-off-by: Dirk Mueller <dmueller@...e.com>
> 
> It would be good to add "Fixes: ed478b3f9e4a" (instead), just to make
> sure this gets fixed everywhere the original problem appears.
> 
> >---
> >  arch/arm64/kernel/cpufeature.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> >diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
> >index f24892a40d2c..c6d80743f4ed 100644
> >--- a/arch/arm64/kernel/cpufeature.c
> >+++ b/arch/arm64/kernel/cpufeature.c
> >@@ -1351,9 +1351,9 @@ static void __update_cpu_capabilities(const struct arm64_cpu_capabilities *caps,
> >  static void update_cpu_capabilities(u16 scope_mask)
> >  {
> >-	__update_cpu_capabilities(arm64_features, scope_mask, "detected:");
> >  	__update_cpu_capabilities(arm64_errata, scope_mask,
> >  				  "enabling workaround for");
> >+	__update_cpu_capabilities(arm64_features, scope_mask, "detected:");
> >  }
> >  static int __enable_cpu_capability(void *arg)
> >@@ -1408,8 +1408,8 @@ __enable_cpu_capabilities(const struct arm64_cpu_capabilities *caps,
> >  static void __init enable_cpu_capabilities(u16 scope_mask)
> >  {
> >-	__enable_cpu_capabilities(arm64_features, scope_mask);
> >  	__enable_cpu_capabilities(arm64_errata, scope_mask);
> >+	__enable_cpu_capabilities(arm64_features, scope_mask);

I forget why these were originally reordered in ed478b3f9e4a.
Was there any real reason for it?

I also notice in that commit that after the detection pass, we set
things up (in update_cpu_capabilities(), enable_cpu_capabilities()) in
the order errata, features.  Does this matter for anything?

Cheers
---Dave

> 
> Reviewed-by: Suzuki K Poulose <suzuki.poulose@....com>
> 
> 
> _______________________________________________
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> linux-arm-kernel@...ts.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

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