linux-kernel - Re: [PATCH v3 01/18] KVM: arm64: Change the layout of enum pkvm_page

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Message-ID: <861py6sht3.wl-maz@kernel.org>
Date: Tue, 17 Dec 2024 10:52:08 +0000
From: Marc Zyngier <maz@...nel.org>
To: Quentin Perret <qperret@...gle.com>
Cc: Oliver Upton <oliver.upton@...ux.dev>,
	Joey Gouly <joey.gouly@....com>,
	Suzuki K Poulose <suzuki.poulose@....com>,
	Zenghui Yu <yuzenghui@...wei.com>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>,
	Fuad Tabba <tabba@...gle.com>,
	Vincent Donnefort <vdonnefort@...gle.com>,
	Sebastian Ene <sebastianene@...gle.com>,
	linux-arm-kernel@...ts.infradead.org,
	kvmarm@...ts.linux.dev,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 01/18] KVM: arm64: Change the layout of enum pkvm_page_state

On Mon, 16 Dec 2024 17:57:46 +0000,
Quentin Perret <qperret@...gle.com> wrote:
> 
> The 'concrete' (a.k.a non-meta) page states are currently encoded using
> software bits in PTEs. For performance reasons, the abstract
> pkvm_page_state enum uses the same bits to encode these states as that
> makes conversions from and to PTEs easy.
> 
> In order to prepare the ground for moving the 'concrete' state storage
> to the hyp vmemmap, re-arrange the enum to use bits 0 and 1 for this
> purpose.
> 
> No functional changes intended.
> 
> Signed-off-by: Quentin Perret <qperret@...gle.com>
> ---
>  arch/arm64/kvm/hyp/include/nvhe/mem_protect.h | 16 +++++++++-------
>  1 file changed, 9 insertions(+), 7 deletions(-)
> 
> diff --git a/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h b/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h
> index 0972faccc2af..8c30362af2b9 100644
> --- a/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h
> +++ b/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h
> @@ -24,25 +24,27 @@
>   */
>  enum pkvm_page_state {
>  	PKVM_PAGE_OWNED			= 0ULL,
> -	PKVM_PAGE_SHARED_OWNED		= KVM_PGTABLE_PROT_SW0,
> -	PKVM_PAGE_SHARED_BORROWED	= KVM_PGTABLE_PROT_SW1,
> -	__PKVM_PAGE_RESERVED		= KVM_PGTABLE_PROT_SW0 |
> -					  KVM_PGTABLE_PROT_SW1,
> +	PKVM_PAGE_SHARED_OWNED		= BIT(0),
> +	PKVM_PAGE_SHARED_BORROWED	= BIT(1),
> +	__PKVM_PAGE_RESERVED		= BIT(0) | BIT(1),
>  
>  	/* Meta-states which aren't encoded directly in the PTE's SW bits */
> -	PKVM_NOPAGE,
> +	PKVM_NOPAGE			= BIT(2),
>  };
> +#define PKVM_PAGE_META_STATES_MASK	(~(BIT(0) | BIT(1)))

Shouldn't that be ~__PKVM_PAGE_RESERVED, given that you just defined it?

>  
>  #define PKVM_PAGE_STATE_PROT_MASK	(KVM_PGTABLE_PROT_SW0 | KVM_PGTABLE_PROT_SW1)
>  static inline enum kvm_pgtable_prot pkvm_mkstate(enum kvm_pgtable_prot prot,
>  						 enum pkvm_page_state state)
>  {
> -	return (prot & ~PKVM_PAGE_STATE_PROT_MASK) | state;
> +	prot &= ~PKVM_PAGE_STATE_PROT_MASK;
> +	prot |= FIELD_PREP(PKVM_PAGE_STATE_PROT_MASK, state);
> +	return prot;
>  }
>  
>  static inline enum pkvm_page_state pkvm_getstate(enum kvm_pgtable_prot prot)
>  {
> -	return prot & PKVM_PAGE_STATE_PROT_MASK;
> +	return FIELD_GET(PKVM_PAGE_STATE_PROT_MASK, prot);
>  }
>  
>  struct host_mmu {

Thanks,

	M.

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