[PATCH v4 56/61] arm64: kvm: avoid CONFIG_PGTABLE_LEVELS for runtime levels

[Marc Zyngier]

On Tue, 12 Sep 2023 15:16:46 +0100,
Ard Biesheuvel <ardb at google.com> wrote:
> 
> From: Ard Biesheuvel <ardb at kernel.org>
> 
> get_user_mapping_size() uses vabits_actual and CONFIG_PGTABLE_LEVELS to
> provide the starting point for a table walk. This is fine for LVA, as
> the number of translation levels is the same regardless of whether LVA
> is enabled. However, with LPA2, this will no longer be the case, so
> let's derive the number of levels from the number of VA bits directly.
> 
> Signed-off-by: Ard Biesheuvel <ardb at kernel.org>
> ---
>  arch/arm64/kvm/mmu.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> index beee6408534d..a4c5d7f44e32 100644
> --- a/arch/arm64/kvm/mmu.c
> +++ b/arch/arm64/kvm/mmu.c
> @@ -802,7 +802,7 @@ static int get_user_mapping_size(struct kvm *kvm, u64 addr)
>  		.pgd		= (kvm_pteref_t)kvm->mm->pgd,
>  		.ia_bits	= vabits_actual,
>  		.start_level	= (KVM_PGTABLE_MAX_LEVELS -
> -				   CONFIG_PGTABLE_LEVELS),
> +				   ARM64_HW_PGTABLE_LEVELS(pgt.ia_bits)),
>  		.mm_ops		= &kvm_user_mm_ops,
>  	};
>  	unsigned long flags;

Note: this walker is going away in 6.7 and we will rely on the folio
infrastructure to avoid the userspace walk.

Acked-by: Marc Zyngier <maz at kernel.org>

	M.

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