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

[Quentin Perret]

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 at kernel.org>
Signed-off-by: Quentin Perret <qperret at 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 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