linux-kernel - Re: [PATCH 2/6] KVM: arm64: Use 0b11 for encoding PKVM

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Message-ID: <86cyejooq2.wl-maz@kernel.org>
Date: Fri, 14 Mar 2025 11:07:01 +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>,
	Vincent Donnefort <vdonnefort@...gle.com>,
	linux-arm-kernel@...ts.infradead.org,
	kvmarm@...ts.linux.dev,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/6] KVM: arm64: Use 0b11 for encoding PKVM_NOPAGE

On Thu, 27 Feb 2025 00:33:06 +0000,
Quentin Perret <qperret@...gle.com> wrote:
> 
> The page ownership state encoded as 0b11 is currently considered
> reserved for future use, and PKVM_NOPAGE uses bit 2. In order to
> simplify the relocation of the hyp ownership state into the
> vmemmap in later patches, let's use the 'reserved' encoding for
> the PKVM_NOPAGE state. The struct hyp_page layout isn't guaranteed
> stable at all, so there is no real reason to have 'reserved' encodings.
> 
> No functional changes intended.
> 
> Signed-off-by: Quentin Perret <qperret@...gle.com>
> ---
>  arch/arm64/kvm/hyp/include/nvhe/memory.h | 5 +----
>  1 file changed, 1 insertion(+), 4 deletions(-)
> 
> diff --git a/arch/arm64/kvm/hyp/include/nvhe/memory.h b/arch/arm64/kvm/hyp/include/nvhe/memory.h
> index 34233d586060..642b5e05fe77 100644
> --- a/arch/arm64/kvm/hyp/include/nvhe/memory.h
> +++ b/arch/arm64/kvm/hyp/include/nvhe/memory.h
> @@ -13,18 +13,15 @@
>   *   01: The page is owned by the page-table owner, but is shared
>   *       with another entity.
>   *   10: The page is shared with, but not owned by the page-table owner.
> - *   11: Reserved for future use (lending).
>   */
>  enum pkvm_page_state {
>  	PKVM_PAGE_OWNED			= 0ULL,
>  	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			= BIT(2),
> +	PKVM_NOPAGE			= BIT(0) | BIT(1),

Isn't this comment stale now?

	M.

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