linux-kernel - Re: [PATCH 1/4] arm64: cpufeature: Effectively expose FRINT capability to userspace

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Message-ID: <20191004103632.lnkyxq2h2owdf7c4@willie-the-truck>
Date:   Fri, 4 Oct 2019 11:36:33 +0100
From:   Will Deacon <will@...nel.org>
To:     Julien Grall <julien.grall@....com>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        catalin.marinas@....com, suzuki.poulose@....com, mark.brown@....com
Subject: Re: [PATCH 1/4] arm64: cpufeature: Effectively expose FRINT
 capability to userspace

On Thu, Oct 03, 2019 at 12:12:08PM +0100, Julien Grall wrote:
> The HWCAP framework will detect a new capability based on the sanitized
> version of the ID registers.
> 
> Sanitization is based on a whitelist, so any field not described will end
> up to be zeroed.
> 
> At the moment, ID_AA64ISAR1_EL1.FRINTTS is not described in
> ftr_id_aa64isar1. This means the field will be zeroed and therefore the
> userspace will not be able to see the HWCAP even if the hardware
> supports the feature.
> 
> This can be fixed by describing the field in ftr_id_aa64isar1.
> 
> Fixes: ca9503fc9e98 ("arm64: Expose FRINT capabilities to userspace")
> Signed-off-by: Julien Grall <julien.grall@....com>
> Cc: mark.brown@....com
> ---
>  arch/arm64/kernel/cpufeature.c | 1 +
>  1 file changed, 1 insertion(+)

D'oh, we should've caught this in testing. Queued as a fix.

Will