The hypervisor will soon be in charge of tracking ownership of all
memory pages in the system. The current page-tracking infrastructure at
EL2 only allows binary states: a page is either owned or not by an
entity. But a number of use-cases will require more complex states for
pages that are shared between two entities (host, hypervisor, or guests).
In preparation for supporting these use-cases, introduce in the KVM
page-table library some infrastructure allowing to tag shared pages
using ignored bits (a.k.a. software bits) in PTEs.
Signed-off-by: Quentin Perret <qperret@xxxxxxxxxx>
---
arch/arm64/include/asm/kvm_pgtable.h | 5 +++++
arch/arm64/kvm/hyp/pgtable.c | 25 +++++++++++++++++++++++++
2 files changed, 30 insertions(+)
diff --git a/arch/arm64/include/asm/kvm_pgtable.h b/arch/arm64/include/asm/kvm_pgtable.h
index dd72653314c7..f6d3d5c8910d 100644
--- a/arch/arm64/include/asm/kvm_pgtable.h
+++ b/arch/arm64/include/asm/kvm_pgtable.h
@@ -81,6 +81,8 @@ 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_STATE_SHARED: Page shared with another entity.
+ * @KVM_PGTABLE_STATE_BORROWED: Page borrowed from another entity.
*/
enum kvm_pgtable_prot {
KVM_PGTABLE_PROT_X = BIT(0),
@@ -88,6 +90,9 @@ enum kvm_pgtable_prot {
KVM_PGTABLE_PROT_R = BIT(2),
KVM_PGTABLE_PROT_DEVICE = BIT(3),
+
+ KVM_PGTABLE_STATE_SHARED = BIT(4),
+ KVM_PGTABLE_STATE_BORROWED = BIT(5),
};
#define KVM_PGTABLE_PROT_RW (KVM_PGTABLE_PROT_R | KVM_PGTABLE_PROT_W)
diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
index 5bdbe7a31551..51598b79dafc 100644
--- a/arch/arm64/kvm/hyp/pgtable.c
+++ b/arch/arm64/kvm/hyp/pgtable.c
@@ -211,6 +211,29 @@ static kvm_pte_t kvm_init_invalid_leaf_owner(u8 owner_id)
return FIELD_PREP(KVM_INVALID_PTE_OWNER_MASK, owner_id);
}
+static kvm_pte_t pte_ignored_bit_prot(enum kvm_pgtable_prot prot)
+{
+ kvm_pte_t ignored_bits = 0;
+
+ /*
+ * Ignored bits 0 and 1 are reserved to track the memory ownership
+ * state of each page:
+ * 00: The page is owned solely by the page-table owner.
+ * 01: The page is owned by the page-table owner, but is shared
+ * with another entity.
+ * 10: The page is shared with, but not owned by the page-table owner.
+ * 11: Reserved for future use (lending).
+ */
+ if (prot & KVM_PGTABLE_STATE_SHARED) {
+ if (prot & KVM_PGTABLE_STATE_BORROWED)
+ ignored_bits |= BIT(1);
+ else
+ ignored_bits |= BIT(0);
+ }
+
+ return FIELD_PREP(KVM_PTE_LEAF_ATTR_IGNORED, ignored_bits);
+}
+
static int kvm_pgtable_visitor_cb(struct kvm_pgtable_walk_data *data, u64 addr,
u32 level, kvm_pte_t *ptep,
enum kvm_pgtable_walk_flags flag)
@@ -357,6 +380,7 @@ 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 |= pte_ignored_bit_prot(prot);
*ptep = attr;
return 0;
@@ -558,6 +582,7 @@ 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 |= pte_ignored_bit_prot(prot);
*ptep = attr;
return 0;
--
2.32.0.402.g57bb445576-goog
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