[PATCH v5 05/69] KVM: arm64: Allow preservation of the S2 SW bits

[Alexandru Elisei]

Hi Marc,

On Mon, Nov 29, 2021 at 08:00:46PM +0000, Marc Zyngier wrote:
> The S2 page table code has a limited use the SW bits, but we are about
> to need them to encode some guest Stage-2 information (its mapping size
> in the form of the TTL encoding).
> 
> Propagate the SW bits specified by the caller, and store them into
> the corresponding entry.
> 
> Signed-off-by: Marc Zyngier <maz at kernel.org>
> ---
>  arch/arm64/kvm/hyp/pgtable.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
> index 8cdbc43fa651..d69e400b2de6 100644
> --- a/arch/arm64/kvm/hyp/pgtable.c
> +++ b/arch/arm64/kvm/hyp/pgtable.c
> @@ -1064,9 +1064,6 @@ int kvm_pgtable_stage2_relax_perms(struct kvm_pgtable *pgt, u64 addr,
>  	u32 level;
>  	kvm_pte_t set = 0, clr = 0;
>  
> -	if (prot & KVM_PTE_LEAF_ATTR_HI_SW)
> -		return -EINVAL;
> -
>  	if (prot & KVM_PGTABLE_PROT_R)
>  		set |= KVM_PTE_LEAF_ATTR_LO_S2_S2AP_R;
>  
> @@ -1076,6 +1073,10 @@ int kvm_pgtable_stage2_relax_perms(struct kvm_pgtable *pgt, u64 addr,
>  	if (prot & KVM_PGTABLE_PROT_X)
>  		clr |= KVM_PTE_LEAF_ATTR_HI_S2_XN;
>  
> +	/* Always propagate the SW bits */
> +	clr |= FIELD_PREP(KVM_PTE_LEAF_ATTR_HI_SW, 0xf);

Nitpick: isn't that the same as:

	clr |= KVM_PTE_LEAF_ATTR_HI_SW;

which looks more readable to me.

> +	set |= prot & KVM_PTE_LEAF_ATTR_HI_SW;

Checked stage2_attr_walker() callbak, first it clears the bits in clr, then
sets the bits in set, so this looks correct to me:

Reviewed-by: Alexandru Elisei <alexandru.elisei at arm.com>

Thanks,
Alex

> +
>  	ret = stage2_update_leaf_attrs(pgt, addr, 1, set, clr, NULL, &level);
>  	if (!ret)
>  		kvm_call_hyp(__kvm_tlb_flush_vmid_ipa, pgt->mmu, addr, level);
> -- 
> 2.30.2
>