[PATCH v4 16/21] KVM: arm64: Add support for relaxing stage-2 perms in generic page-table code

[Alexandru Elisei]

Hi Will,

Minor nitpick below.

On 9/7/20 4:23 PM, Will Deacon wrote:
> Add support for relaxing the permissions of a stage-2 mapping (i.e.
> adding additional permissions) to the generic page-table code.
>
> Cc: Marc Zyngier <maz at kernel.org>
> Cc: Quentin Perret <qperret at google.com>
> Reviewed-by: Gavin Shan <gshan at redhat.com>
> Signed-off-by: Will Deacon <will at kernel.org>
> ---
>  arch/arm64/include/asm/kvm_pgtable.h | 17 +++++++++++++++++
>  arch/arm64/kvm/hyp/pgtable.c         | 20 ++++++++++++++++++++
>  2 files changed, 37 insertions(+)
>
> diff --git a/arch/arm64/include/asm/kvm_pgtable.h b/arch/arm64/include/asm/kvm_pgtable.h
> index a776bcf74316..5ab4f852a463 100644
> --- a/arch/arm64/include/asm/kvm_pgtable.h
> +++ b/arch/arm64/include/asm/kvm_pgtable.h
> @@ -218,6 +218,23 @@ kvm_pte_t kvm_pgtable_stage2_mkyoung(struct kvm_pgtable *pgt, u64 addr);
>   */
>  kvm_pte_t kvm_pgtable_stage2_mkold(struct kvm_pgtable *pgt, u64 addr);
>  
> +/**
> + * kvm_pgtable_stage2_relax_perms() - Relax the permissions enforced by a
> + *				      page-table entry.
> + * @pgt:	Page-table structure initialised by kvm_pgtable_stage2_init().
> + * @addr:	Intermediate physical address to identify the page-table entry.
> + * @prot:	Additional permissions to grant for the mapping.
> + *
> + * If there is a valid, leaf page-table entry used to translate @addr, then
> + * relax the permissions in that entry according to the read, write and
> + * execute permissions specified by @prot. No permissions are removed, and
> + * TLB invalidation is performed after updating the entry.
> + *
> + * Return: 0 on success, negative error code on failure.
> + */
> +int kvm_pgtable_stage2_relax_perms(struct kvm_pgtable *pgt, u64 addr,
> +				   enum kvm_pgtable_prot prot);
> +
>  /**
>   * kvm_pgtable_stage2_is_young() - Test whether a page-table entry has the
>   *				   access flag set.
> diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
> index ad18ce469041..df705533dc3f 100644
> --- a/arch/arm64/kvm/hyp/pgtable.c
> +++ b/arch/arm64/kvm/hyp/pgtable.c
> @@ -782,6 +782,26 @@ bool kvm_pgtable_stage2_is_young(struct kvm_pgtable *pgt, u64 addr)
>  	return pte & KVM_PTE_LEAF_ATTR_LO_S2_AF;
>  }
>  
> +int kvm_pgtable_stage2_relax_perms(struct kvm_pgtable *pgt, u64 addr,
> +				   enum kvm_pgtable_prot prot)
> +{
> +	int ret;
> +	kvm_pte_t set = 0, clr = 0;
> +
> +	if (prot & KVM_PGTABLE_PROT_R)
> +		set |= KVM_PTE_LEAF_ATTR_LO_S2_S2AP_R;
> +
> +	if (prot & KVM_PGTABLE_PROT_W)
> +		set |= KVM_PTE_LEAF_ATTR_LO_S2_S2AP_W;
> +
> +	if (prot & KVM_PGTABLE_PROT_X)
> +		clr |= KVM_PTE_LEAF_ATTR_HI_S2_XN;
> +
> +	ret = stage2_update_leaf_attrs(pgt, addr, 1, set, clr, NULL);
> +	kvm_call_hyp(__kvm_tlb_flush_vmid_ipa, pgt->mmu, addr, 0);

The level 0 argument could be replaced by S2_NO_LEVEL_HINT, which is self
explanatory. However, that means the file needs to include stage2_pgtable.h.

Thanks,
Alex
> +	return ret;
> +}
> +
>  static int stage2_flush_walker(u64 addr, u64 end, u32 level, kvm_pte_t *ptep,
>  			       enum kvm_pgtable_walk_flags flag,
>  			       void * const arg)