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 <[email protected]> --- 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 _______________________________________________ kvmarm mailing list [email protected] https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
