linux-kernel - Re: [PATCH v3 4/6] arm64: nvhe: Convert the opencoded field modify

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Message-ID: <86r01rjald.wl-maz@kernel.org>
Date: Thu, 17 Apr 2025 12:23:10 +0100
From: Marc Zyngier <maz@...nel.org>
To: Luo Jie <quic_luoj@...cinc.com>
Cc: Yury Norov <yury.norov@...il.com>,
	Rasmus Villemoes
	<linux@...musvillemoes.dk>,
	Julia Lawall <Julia.Lawall@...ia.fr>,
	"Nicolas\
 Palix" <nicolas.palix@...g.fr>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>,
	Oliver Upton
	<oliver.upton@...ux.dev>,
	Joey Gouly <joey.gouly@....com>,
	Suzuki K Poulose
	<suzuki.poulose@....com>,
	Zenghui Yu <yuzenghui@...wei.com>,
	<linux-kernel@...r.kernel.org>,
	<cocci@...ia.fr>,
	<linux-arm-kernel@...ts.infradead.org>,
	<kvmarm@...ts.linux.dev>,
	<andrew@...n.ch>,
	<quic_kkumarcs@...cinc.com>,
	<quic_linchen@...cinc.com>,
	<quic_leiwei@...cinc.com>,
	<quic_suruchia@...cinc.com>,
	<quic_pavir@...cinc.com>
Subject: Re: [PATCH v3 4/6] arm64: nvhe: Convert the opencoded field modify

On Thu, 17 Apr 2025 11:47:11 +0100,
Luo Jie <quic_luoj@...cinc.com> wrote:
> 
> Replaced below code with the wrapper FIELD_MODIFY(MASK, &reg, val)
> - reg &= ~MASK;
> - reg |= FIELD_PREP(MASK, val);
> The semantic patch that makes this change is available
> in scripts/coccinelle/misc/field_modify.cocci.
> 
> More information about semantic patching is available at
> https://coccinelle.gitlabpages.inria.fr/website
> 
> Signed-off-by: Luo Jie <quic_luoj@...cinc.com>
> ---
>  arch/arm64/kvm/hyp/include/nvhe/memory.h | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/arch/arm64/kvm/hyp/include/nvhe/memory.h b/arch/arm64/kvm/hyp/include/nvhe/memory.h
> index 34233d586060..b2af748964d0 100644
> --- a/arch/arm64/kvm/hyp/include/nvhe/memory.h
> +++ b/arch/arm64/kvm/hyp/include/nvhe/memory.h
> @@ -30,8 +30,7 @@ enum pkvm_page_state {
>  static inline enum kvm_pgtable_prot pkvm_mkstate(enum kvm_pgtable_prot prot,
>  						 enum pkvm_page_state state)
>  {
> -	prot &= ~PKVM_PAGE_STATE_PROT_MASK;
> -	prot |= FIELD_PREP(PKVM_PAGE_STATE_PROT_MASK, state);
> +	FIELD_MODIFY(PKVM_PAGE_STATE_PROT_MASK, &prot, state);
>  	return prot;
>  }

Following up on my suggestion to *not* add anything new, this patch
could be written as:

diff --git a/arch/arm64/kvm/hyp/include/nvhe/memory.h b/arch/arm64/kvm/hyp/include/nvhe/memory.h
index 34233d5860607..08cb6ba0e0716 100644
--- a/arch/arm64/kvm/hyp/include/nvhe/memory.h
+++ b/arch/arm64/kvm/hyp/include/nvhe/memory.h
@@ -30,9 +30,8 @@ enum pkvm_page_state {
 static inline enum kvm_pgtable_prot pkvm_mkstate(enum kvm_pgtable_prot prot,
 						 enum pkvm_page_state state)
 {
-	prot &= ~PKVM_PAGE_STATE_PROT_MASK;
-	prot |= FIELD_PREP(PKVM_PAGE_STATE_PROT_MASK, state);
-	return prot;
+	u64 p = prot;
+	return u64_replace_bits(p, state, PKVM_PAGE_STATE_PROT_MASK);
 }
 
 static inline enum pkvm_page_state pkvm_getstate(enum kvm_pgtable_prot prot)

	M.

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