Re: [PATCH 17/22] KVM: arm64: Set Access flag on table descriptors at stage-1

[Leonardo Bras <leo.bras@arm.com>]

On Tue, Jun 23, 2026 at 11:41:56AM -0700, Oliver Upton wrote:
> Implement access flag updates on table descriptors as required by
> FEAT_HAFT. Note that unlike leaf descriptors, access flags on table
> descriptors never generate a fault.
> 
> Signed-off-by: Oliver Upton <oupton@kernel.org>
> ---
> 
> Same comment as TCR_ELx.HD, will fix in v2.
> 
>  arch/arm64/include/asm/kvm_nested.h  |  1 +
>  arch/arm64/include/asm/kvm_pgtable.h | 11 +++++++++++
>  arch/arm64/kvm/at.c                  | 11 ++++++++++-
>  arch/arm64/kvm/hyp/pgtable.c         | 11 -----------
>  4 files changed, 22 insertions(+), 12 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/kvm_nested.h b/arch/arm64/include/asm/kvm_nested.h
> index 1bb070328b1c..b52cf869333c 100644
> --- a/arch/arm64/include/asm/kvm_nested.h
> +++ b/arch/arm64/include/asm/kvm_nested.h
> @@ -317,6 +317,7 @@ struct s1_walk_info {
>  	bool			pa52bit;
>  	bool			ha;
>  	bool			hd;
> +	bool			haft;
>  };
>  
>  struct s1_walk_result {
> diff --git a/arch/arm64/include/asm/kvm_pgtable.h b/arch/arm64/include/asm/kvm_pgtable.h
> index 6ae36973686c..67601ed6370d 100644
> --- a/arch/arm64/include/asm/kvm_pgtable.h
> +++ b/arch/arm64/include/asm/kvm_pgtable.h
> @@ -131,6 +131,17 @@ static inline bool kvm_pte_valid(kvm_pte_t pte)
>  	return pte & KVM_PTE_VALID;
>  }
>  
> +static inline bool kvm_pte_table(kvm_pte_t pte, s8 level)
> +{
> +	if (level == KVM_PGTABLE_LAST_LEVEL)
> +		return false;
> +
> +	if (!kvm_pte_valid(pte))
> +		return false;
> +
> +	return FIELD_GET(KVM_PTE_TYPE, pte) == KVM_PTE_TYPE_TABLE;
> +}
> +

Moved here for availability.

>  static inline u64 kvm_pte_to_phys(kvm_pte_t pte)
>  {
>  	u64 pa;
> diff --git a/arch/arm64/kvm/at.c b/arch/arm64/kvm/at.c
> index 8d76eaf463c9..31a55b9d3385 100644
> --- a/arch/arm64/kvm/at.c
> +++ b/arch/arm64/kvm/at.c
> @@ -416,6 +416,8 @@ static int setup_s1_walk(struct kvm_vcpu *vcpu, struct s1_walk_info *wi,
>  	wi->hd &= (wi->regime == TR_EL2 ?
>  		  FIELD_GET(TCR_EL2_HD, tcr) :
>  		  FIELD_GET(TCR_HD, tcr));
> +	wi->haft  = kvm_has_feat(vcpu->kvm, ID_AA64MMFR1_EL1, HAFDBS, HAFT) &&
> +		    FIELD_GET(TCR2_EL1_HAFT, effective_tcr2(vcpu, wi->regime));
>  
>  	return 0;
>  
> @@ -465,7 +467,7 @@ static bool should_set_access_flag(struct s1_walk_info *wi, struct s1_walk_step
>  	if (access->type == WALK_ACCESS_NONARCH)
>  		return false;
>  
> -	return wi->ha;
> +	return kvm_pte_table(ws->desc, ws->level) ? wi->haft : wi->ha;
>  }
>  

Right, adding support for tables' Access flag.


>  static bool should_set_dirty_state(struct s1_walk_info *wi, struct s1_walk_step *ws,
> @@ -473,6 +475,9 @@ static bool should_set_dirty_state(struct s1_walk_info *wi, struct s1_walk_step
>  {
>  	bool perm = wi->as_el0 ? wr->uw : wr->pw;
>  
> +	if (kvm_pte_table(ws->desc, ws->level))
> +		return false;
> +

Right, tables don't get dirty/writable.


>  	switch (access->type) {
>  	/* R_RKMHW */
>  	case WALK_ACCESS_CMO:
> @@ -620,6 +625,10 @@ static int walk_s1(struct kvm_vcpu *vcpu, struct s1_walk_info *wi,
>  		if (ws.level == 3)
>  			break;
>  
> +		ret = handle_desc_update(vcpu, wi, &ws, wr, access);
> +		if (ret)
> +			return ret;
> +

And this is to update the table descriptor, IIUC.

If I got that right, then FWIW:
Reviewed-by: Leonardo Bras <leo.bras@arm.com>

Thanks!
Leo