Re: [PATCH v4 11/21] KVM: arm64: Allow populating software bits

From: Fuad Tabba
Date: Tue Aug 10 2021 - 00:57:35 EST


Hi Quentin,

On Mon, Aug 9, 2021 at 5:25 PM Quentin Perret <qperret@xxxxxxxxxx> wrote:
>
> Introduce infrastructure allowing to manipulate software bits in stage-1
> and stage-2 page-tables using additional entries in the kvm_pgtable_prot
> enum.
>
> This is heavily inspired by Marc's implementation of a similar feature
> in the NV patch series, but adapted to allow stage-1 changes as well:
>
> https://lore.kernel.org/kvmarm/20210510165920.1913477-56-maz@xxxxxxxxxx/
>
> Suggested-by: Marc Zyngier <maz@xxxxxxxxxx>
> Signed-off-by: Quentin Perret <qperret@xxxxxxxxxx>
> ---

Reviewed-by: Fuad Tabba <tabba@xxxxxxxxxx>

Thanks,
/fuad

> arch/arm64/include/asm/kvm_pgtable.h | 12 +++++++++++-
> arch/arm64/kvm/hyp/pgtable.c | 5 +++++
> 2 files changed, 16 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm64/include/asm/kvm_pgtable.h b/arch/arm64/include/asm/kvm_pgtable.h
> index 2c090b0eee77..ff9d52f8073a 100644
> --- a/arch/arm64/include/asm/kvm_pgtable.h
> +++ b/arch/arm64/include/asm/kvm_pgtable.h
> @@ -121,6 +121,10 @@ enum kvm_pgtable_stage2_flags {
> * @KVM_PGTABLE_PROT_W: Write permission.
> * @KVM_PGTABLE_PROT_R: Read permission.
> * @KVM_PGTABLE_PROT_DEVICE: Device attributes.
> + * @KVM_PGTABLE_PROT_SW0: Software bit 0.
> + * @KVM_PGTABLE_PROT_SW1: Software bit 1.
> + * @KVM_PGTABLE_PROT_SW2: Software bit 2.
> + * @KVM_PGTABLE_PROT_SW3: Software bit 3.
> */
> enum kvm_pgtable_prot {
> KVM_PGTABLE_PROT_X = BIT(0),
> @@ -128,6 +132,11 @@ enum kvm_pgtable_prot {
> KVM_PGTABLE_PROT_R = BIT(2),
>
> KVM_PGTABLE_PROT_DEVICE = BIT(3),
> +
> + KVM_PGTABLE_PROT_SW0 = BIT(55),
> + KVM_PGTABLE_PROT_SW1 = BIT(56),
> + KVM_PGTABLE_PROT_SW2 = BIT(57),
> + KVM_PGTABLE_PROT_SW3 = BIT(58),
> };
>
> #define KVM_PGTABLE_PROT_RW (KVM_PGTABLE_PROT_R | KVM_PGTABLE_PROT_W)
> @@ -420,7 +429,8 @@ kvm_pte_t kvm_pgtable_stage2_mkold(struct kvm_pgtable *pgt, u64 addr);
> * 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.
> + * TLB invalidation is performed after updating the entry. Software bits cannot
> + * be set or cleared using kvm_pgtable_stage2_relax_perms().
> *
> * Return: 0 on success, negative error code on failure.
> */
> diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
> index e25d829587b9..cff744136044 100644
> --- a/arch/arm64/kvm/hyp/pgtable.c
> +++ b/arch/arm64/kvm/hyp/pgtable.c
> @@ -357,6 +357,7 @@ static int hyp_set_prot_attr(enum kvm_pgtable_prot prot, kvm_pte_t *ptep)
> attr |= FIELD_PREP(KVM_PTE_LEAF_ATTR_LO_S1_AP, ap);
> attr |= FIELD_PREP(KVM_PTE_LEAF_ATTR_LO_S1_SH, sh);
> attr |= KVM_PTE_LEAF_ATTR_LO_S1_AF;
> + attr |= prot & KVM_PTE_LEAF_ATTR_HI_SW;
> *ptep = attr;
>
> return 0;
> @@ -558,6 +559,7 @@ static int stage2_set_prot_attr(struct kvm_pgtable *pgt, enum kvm_pgtable_prot p
>
> attr |= FIELD_PREP(KVM_PTE_LEAF_ATTR_LO_S2_SH, sh);
> attr |= KVM_PTE_LEAF_ATTR_LO_S2_AF;
> + attr |= prot & KVM_PTE_LEAF_ATTR_HI_SW;
> *ptep = attr;
>
> return 0;
> @@ -1025,6 +1027,9 @@ 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;
>
> --
> 2.32.0.605.g8dce9f2422-goog
>