linux-kernel - Re: [PATCH v4 2/5] KVM: arm64: Make stage2_has

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Message-ID: <aCyX2nJzBXmQarAJ@linux.dev>
Date: Tue, 20 May 2025 07:55:22 -0700
From: Oliver Upton <oliver.upton@...ux.dev>
To: ankita@...dia.com
Cc: jgg@...dia.com, maz@...nel.org, joey.gouly@....com,
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Subject: Re: [PATCH v4 2/5] KVM: arm64: Make stage2_has_fwb global scope

Hi Ankit,

On Sun, May 18, 2025 at 05:47:51AM +0000, ankita@...dia.com wrote:
> From: Ankit Agrawal <ankita@...dia.com>
> 
> Change the scope of stage2_has_fwb as it will be used in
> broader KVM code to determine whether the FWB feature is
> supported by the hardware.

Please just use the cpucap directly outside of the page table code. The
only non-FWB stage-2 that KVM maintains on a FEAT_S2FWB machine is for
the host when using protected mode. I don't anticipate that changing any
time soon.

Thanks,
Oliver

> ---
>  arch/arm64/include/asm/kvm_pgtable.h | 8 ++++++++
>  arch/arm64/kvm/hyp/pgtable.c         | 2 +-
>  2 files changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/include/asm/kvm_pgtable.h b/arch/arm64/include/asm/kvm_pgtable.h
> index 6b9d274052c7..f21e2fae2bfe 100644
> --- a/arch/arm64/include/asm/kvm_pgtable.h
> +++ b/arch/arm64/include/asm/kvm_pgtable.h
> @@ -507,6 +507,14 @@ u64 kvm_pgtable_hyp_unmap(struct kvm_pgtable *pgt, u64 addr, u64 size);
>   */
>  u64 kvm_get_vtcr(u64 mmfr0, u64 mmfr1, u32 phys_shift);
>  
> +/**
> + * stage2_has_fwb() - Determine whether FWB is supported
> + * @pgt:    Page-table structure initialised by kvm_pgtable_stage2_init*()
> + *
> + * Return: True if FWB is supported.
> + */
> +bool stage2_has_fwb(struct kvm_pgtable *pgt);
> +
>  /**
>   * kvm_pgtable_stage2_pgd_size() - Helper to compute size of a stage-2 PGD
>   * @vtcr:	Content of the VTCR register.
> diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
> index df5cc74a7dd0..ee6b98fefd61 100644
> --- a/arch/arm64/kvm/hyp/pgtable.c
> +++ b/arch/arm64/kvm/hyp/pgtable.c
> @@ -637,7 +637,7 @@ u64 kvm_get_vtcr(u64 mmfr0, u64 mmfr1, u32 phys_shift)
>  	return vtcr;
>  }
>  
> -static bool stage2_has_fwb(struct kvm_pgtable *pgt)
> +bool stage2_has_fwb(struct kvm_pgtable *pgt)
>  {
>  	if (!cpus_have_final_cap(ARM64_HAS_STAGE2_FWB))
>  		return false;
> -- 
> 2.34.1
>