linux-kernel - Re: [PATCH 2/4] arm64/sysreg: Replace TCR

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Message-ID: <87jz30my30.wl-maz@kernel.org>
Date: Mon, 18 Aug 2025 16:46:59 +0100
From: Marc Zyngier <maz@...nel.org>
To: Anshuman Khandual <anshuman.khandual@....com>
Cc: linux-arm-kernel@...ts.infradead.org,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>,
	Oliver Upton <oliver.upton@...ux.dev>,
	Mark Brown <broonie@...nel.org>,
	Ryan Roberts <ryan.roberts@....com>,
	kvmarm@...ts.linux.dev,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/4] arm64/sysreg: Replace TCR_EL1 field macros

On Mon, 18 Aug 2025 05:57:57 +0100,
Anshuman Khandual <anshuman.khandual@....com> wrote:
> 
> This just replaces all used TCR_EL1 field macros with tools sysreg variant
> based fields and subsequently drops them from the header (pgtable-hwdef.h).
> While here, also drop all the unused TCR_XXX macros from the header.
> 
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: Will Deacon <will@...nel.org>
> Cc: Marc Zyngier <maz@...nel.org>
> Cc: Mark Brown <broonie@...nel.org>
> Cc: kvmarm@...ts.linux.dev
> Cc: linux-arm-kernel@...ts.infradead.org
> Cc: linux-kernel@...r.kernel.org
> Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>
> ---
>  arch/arm64/include/asm/assembler.h         |   6 +-
>  arch/arm64/include/asm/cputype.h           |   2 +-
>  arch/arm64/include/asm/kvm_arm.h           |  28 +++---
>  arch/arm64/include/asm/kvm_nested.h        |   6 +-
>  arch/arm64/include/asm/mmu_context.h       |   4 +-
>  arch/arm64/include/asm/pgtable-hwdef.h     | 107 +++------------------
>  arch/arm64/include/asm/pgtable-prot.h      |   2 +-
>  arch/arm64/kernel/cpufeature.c             |   4 +-
>  arch/arm64/kernel/pi/map_kernel.c          |   8 +-
>  arch/arm64/kernel/vmcore_info.c            |   2 +-
>  arch/arm64/kvm/arm.c                       |   6 +-
>  arch/arm64/kvm/at.c                        |  48 ++++-----
>  arch/arm64/kvm/hyp/include/hyp/switch.h    |   2 +-
>  arch/arm64/kvm/hyp/include/hyp/sysreg-sr.h |   2 +-
>  arch/arm64/kvm/hyp/nvhe/switch.c           |   2 +-
>  arch/arm64/kvm/hyp/nvhe/tlb.c              |   2 +-
>  arch/arm64/kvm/hyp/vhe/tlb.c               |   2 +-
>  arch/arm64/kvm/nested.c                    |   8 +-
>  arch/arm64/kvm/pauth.c                     |  12 +--
>  arch/arm64/mm/proc.S                       |  29 +++---
>  tools/arch/arm64/include/asm/cputype.h     |   2 +-
>  21 files changed, 101 insertions(+), 183 deletions(-)

[...]

> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
> index 888f7c7abf54..b47d6d530e57 100644
> --- a/arch/arm64/kvm/arm.c
> +++ b/arch/arm64/kvm/arm.c
> @@ -2000,10 +2000,10 @@ static void __init cpu_prepare_hyp_mode(int cpu, u32 hyp_va_bits)
>  
>  	tcr = read_sysreg(tcr_el1);
>  	if (cpus_have_final_cap(ARM64_KVM_HVHE)) {
> -		tcr &= ~(TCR_HD | TCR_HA | TCR_A1 | TCR_T0SZ_MASK);
> -		tcr |= TCR_EPD1_MASK;
> +		tcr &= ~(TCR_EL1_HD | TCR_EL1_HA | TCR_EL1_A1 | TCR_EL1_T0SZ_MASK);
> +		tcr |= TCR_EL1_EPD1_MASK;

Except that none of that code is about EL1. At all.

>  	} else {
> -		unsigned long ips = FIELD_GET(TCR_IPS_MASK, tcr);
> +		unsigned long ips = FIELD_GET(TCR_EL1_IPS_MASK, tcr);
>  
>  		tcr &= TCR_EL2_MASK;
>  		tcr |= TCR_EL2_RES1 | FIELD_PREP(TCR_EL2_PS_MASK, ips);
> diff --git a/arch/arm64/kvm/at.c b/arch/arm64/kvm/at.c
> index 0e5610533949..5f0f10ef38f0 100644
> --- a/arch/arm64/kvm/at.c
> +++ b/arch/arm64/kvm/at.c
> @@ -134,8 +134,8 @@ static int setup_s1_walk(struct kvm_vcpu *vcpu, struct s1_walk_info *wi,
>  	tbi = (wi->regime == TR_EL2 ?
>  	       FIELD_GET(TCR_EL2_TBI, tcr) :
>  	       (va55 ?
> -		FIELD_GET(TCR_TBI1, tcr) :
> -		FIELD_GET(TCR_TBI0, tcr)));
> +		FIELD_GET(TCR_EL1_TBI1, tcr) :
> +		FIELD_GET(TCR_EL1_TBI0, tcr)));

This is the reason number one why I dislike this patch.

Here, we deal with both the EL1&0 *and* the EL2&0 translation
regimes. And I left the original definition *on purpose* so that
nobody would read this code as being EL1-only. Now, you will glance
over it with warm fuzzy feeling that you know what this is about --
purely EL1. And that's what bugs are made of.

Of course, nothing changed functionally. But is it better? No.

	M.

-- 
Jazz isn't dead. It just smells funny.