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Date:   Mon, 19 Jul 2021 13:55:29 +0100
Message-ID: <87im16jwe6.wl-maz@kernel.org>
From:   Marc Zyngier <maz@kernel.org>
To:     Quentin Perret <qperret@google.com>
Cc:     james.morse@arm.com, alexandru.elisei@arm.com,
        suzuki.poulose@arm.com, catalin.marinas@arm.com, will@kernel.org,
        linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu,
        linux-kernel@vger.kernel.org, ardb@kernel.org, qwandor@google.com,
        tabba@google.com, dbrazdil@google.com, kernel-team@android.com
Subject: Re: [PATCH 05/14] KVM: arm64: Don't overwrite ignored bits with owner id
In-Reply-To: <20210719104735.3681732-6-qperret@google.com>
References: <20210719104735.3681732-1-qperret@google.com>
        <20210719104735.3681732-6-qperret@google.com>
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On Mon, 19 Jul 2021 11:47:26 +0100,
Quentin Perret <qperret@google.com> wrote:
> 
> The nVHE protected mode uses invalid mappings in the host stage-2
> page-table to track the owner of each page in the system. In order to
> allow the usage of ignored bits (a.k.a. software bits) in these
> mappings, move the owner encoding away from the top bits.

But that's exactly what the current situation is allowing: the use of
the SW bits. I am guessing that what you really mean is that you want
to *preserve* the SW bits from an existing mapping and use other bits
when the mapping is invalid?

Thanks,

	M.

> 
> Signed-off-by: Quentin Perret <qperret@google.com>
> ---
>  arch/arm64/kvm/hyp/pgtable.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
> index a60653cbd8e5..a0ac8c2bc174 100644
> --- a/arch/arm64/kvm/hyp/pgtable.c
> +++ b/arch/arm64/kvm/hyp/pgtable.c
> @@ -50,7 +50,7 @@
>  					 KVM_PTE_LEAF_ATTR_LO_S2_S2AP_W | \
>  					 KVM_PTE_LEAF_ATTR_HI_S2_XN)
>  
> -#define KVM_INVALID_PTE_OWNER_MASK	GENMASK(63, 56)
> +#define KVM_INVALID_PTE_OWNER_MASK	GENMASK(9, 2)
>  #define KVM_MAX_OWNER_ID		1
>  
>  struct kvm_pgtable_walk_data {
> -- 
> 2.32.0.402.g57bb445576-goog
> 
> 

-- 
Without deviation from the norm, progress is not possible.