linux-kernel - Re: [RFC PATCH 13/27] KVM: arm64: Enable access to sanitized CPU features at EL2

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Message-ID: <20201123132223.oohevce4izuoaqi3@google.com>
Date:   Mon, 23 Nov 2020 13:22:23 +0000
From:   David Brazdil <dbrazdil@...gle.com>
To:     Quentin Perret <qperret@...gle.com>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Marc Zyngier <maz@...nel.org>,
        James Morse <james.morse@....com>,
        Julien Thierry <julien.thierry.kdev@...il.com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        "moderated list:ARM64 PORT (AARCH64 ARCHITECTURE)" 
        <linux-arm-kernel@...ts.infradead.org>,
        open list <linux-kernel@...r.kernel.org>,
        "open list:KERNEL VIRTUAL MACHINE FOR ARM64 (KVM/arm64)" 
        <kvmarm@...ts.cs.columbia.edu>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE" 
        <devicetree@...r.kernel.org>, kernel-team@...roid.com,
        android-kvm@...gle.com
Subject: Re: [RFC PATCH 13/27] KVM: arm64: Enable access to sanitized CPU
 features at EL2

> +int copy_ftr_reg(u32 id, struct arm64_ftr_reg *dst)
> +{
> +	struct arm64_ftr_reg *regp = get_arm64_ftr_reg(id);
> +
> +	if (!regp)
> +		return -EINVAL;
> +
> +	memcpy(dst, regp, sizeof(*regp));
> +
> +	return 0;
> +}
> +
>  #define read_sysreg_case(r)	\
>  	case r:		return read_sysreg_s(r)
>  
> diff --git a/arch/arm64/kernel/image-vars.h b/arch/arm64/kernel/image-vars.h
> index dd8ccc9efb6a..c35d768672eb 100644
> --- a/arch/arm64/kernel/image-vars.h
> +++ b/arch/arm64/kernel/image-vars.h
> @@ -116,6 +116,8 @@ __kvm_nvhe___memcpy			= __kvm_nvhe___pi_memcpy;
>  __kvm_nvhe___memset			= __kvm_nvhe___pi_memset;
>  #endif
>  
> +_kvm_nvhe___flush_dcache_area		= __kvm_nvhe___pi___flush_dcache_area;
> +

Could you help my understand why we need this?
* Why do we need PI routines in the first place? Would my series that fixes
  relocations in hyp code remove the need?
* You added these aliases for the string routines because you were worried
  somebody would change the implementation in arch/arm64/lib, right? But this
  cache flush function is defined in hyp/nvhe. So why do we need to point to
  the PI alias if we control the implementation?