linux-kernel - Re: [PATCH v3 1/2] arm64: Add hypervisor safe helper for checking constant capabilities

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Date:   Tue, 8 Nov 2016 18:11:03 +0000
From:   Will Deacon <will.deacon@....com>
To:     Suzuki K Poulose <suzuki.poulose@....com>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        ard.biesheuvel@...aro.org, catalin.marinas@....com,
        mark.rutland@....com, marc.zyngier@....com,
        kvmarm@...ts.cs.columbia.edu, Robert Ritcher <rritcher@...ium.com>,
        Tirumalesh Chalamarla <tchalamarla@...ium.com>
Subject: Re: [PATCH v3 1/2] arm64: Add hypervisor safe helper for checking
 constant capabilities

On Tue, Nov 08, 2016 at 01:56:20PM +0000, Suzuki K Poulose wrote:
> The hypervisor may not have full access to the kernel data structures
> and hence cannot safely use cpus_have_cap() helper for checking the
> system capability. Add a safe helper for hypervisors to check a constant
> system capability, which *doesn't* fall back to checking the bitmap
> maintained by the kernel. With this, make the cpus_have_cap() only
> check the bitmask and force constant cap checks to use the new API
> for quicker checks.
> 
> Cc: Robert Ritcher <rritcher@...ium.com>
> Cc: Tirumalesh Chalamarla <tchalamarla@...ium.com>
> Cc: Marc Zyngier <marc.zyngier@....com>
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: Will Deacon <will.deacon@....com>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@....com>
> ---
>  arch/arm64/include/asm/cpufeature.h | 19 ++++++++++++-------
>  arch/arm64/kernel/cpufeature.c      |  2 +-
>  arch/arm64/kernel/process.c         |  2 +-
>  drivers/irqchip/irq-gic-v3.c        | 13 +------------

It might be worth having the GIC changes as a separate patch, but either
way:

Reviewed-by: Will Deacon <will.deacon@....com>

Will