[PATCH v2 09/16] KVM: arm64: Allow populating software bits

Quentin Perret
2021-07-26T09:29:43Z

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@kernel.org/

Suggested-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Quentin Perret <qperret@google.com>
---
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 9246a27e2839..0be9f83974ad 100644
--- a/arch/arm64/include/asm/kvm_pgtable.h
+++ b/arch/arm64/include/asm/kvm_pgtable.h
@@ -108,6 +108,10 @@ 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),
@@ -115,6 +119,11 @@ 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)
@@ -406,7 +415,8 @@ 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 e0cd748e4af6..bd409d524dea 100644
--- a/arch/arm64/kvm/hyp/pgtable.c
+++ b/arch/arm64/kvm/hyp/pgtable.c
@@ -370,6 +370,7 @@ 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;
@@ -571,6 +572,7 @@ 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;
@@ -1038,6 +1040,9 @@ 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;

--
2.32.0.432.gabb21c7263-goog