[PATCH v4 12/38] KVM: arm64: Introduce __pkvm_host_donate_guest()

Will Deacon
2026-03-27T14:01:30Z

In preparation for supporting protected VMs, whose memory pages are
isolated from the host, introduce a new pKVM hypercall to allow the
donation of pages to a guest.

Tested-by: Fuad Tabba <tabba@google.com>
Tested-by: Mostafa Saleh <smostafa@google.com>
Signed-off-by: Will Deacon <will@kernel.org>
---
arch/arm64/include/asm/kvm_asm.h | 1 +
arch/arm64/include/asm/kvm_pgtable.h | 2 +-
arch/arm64/kvm/hyp/include/nvhe/mem_protect.h | 2 ++
arch/arm64/kvm/hyp/nvhe/hyp-main.c | 21 +++++++++++++
arch/arm64/kvm/hyp/nvhe/mem_protect.c | 30 +++++++++++++++++++
5 files changed, 55 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/include/asm/kvm_asm.h b/arch/arm64/include/asm/kvm_asm.h
index df6b661701b6..dfc6625c8269 100644
--- a/arch/arm64/include/asm/kvm_asm.h
+++ b/arch/arm64/include/asm/kvm_asm.h
@@ -79,6 +79,7 @@ enum __kvm_host_smccc_func {
/* Hypercalls that are available only when pKVM has finalised. */
__KVM_HOST_SMCCC_FUNC___pkvm_host_share_hyp,
__KVM_HOST_SMCCC_FUNC___pkvm_host_unshare_hyp,
+ __KVM_HOST_SMCCC_FUNC___pkvm_host_donate_guest,
__KVM_HOST_SMCCC_FUNC___pkvm_host_share_guest,
__KVM_HOST_SMCCC_FUNC___pkvm_host_unshare_guest,
__KVM_HOST_SMCCC_FUNC___pkvm_host_relax_perms_guest,
diff --git a/arch/arm64/include/asm/kvm_pgtable.h b/arch/arm64/include/asm/kvm_pgtable.h
index c201168f2857..50caca311ef5 100644
--- a/arch/arm64/include/asm/kvm_pgtable.h
+++ b/arch/arm64/include/asm/kvm_pgtable.h
@@ -100,7 +100,7 @@ typedef u64 kvm_pte_t;
KVM_PTE_LEAF_ATTR_HI_S2_XN)

#define KVM_INVALID_PTE_OWNER_MASK GENMASK(9, 2)
-#define KVM_MAX_OWNER_ID 1
+#define KVM_MAX_OWNER_ID 2

/*
* Used to indicate a pte for which a 'break-before-make' sequence is in
diff --git a/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h b/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h
index 7f25f2bca90c..7061b0be340a 100644
--- a/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h
+++ b/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h
@@ -27,6 +27,7 @@ extern struct host_mmu host_mmu;
enum pkvm_component_id {
PKVM_ID_HOST,
PKVM_ID_HYP,
+ PKVM_ID_GUEST,
};

extern unsigned long hyp_nr_cpus;
@@ -38,6 +39,7 @@ int __pkvm_host_donate_hyp(u64 pfn, u64 nr_pages);
int __pkvm_hyp_donate_host(u64 pfn, u64 nr_pages);
int __pkvm_host_share_ffa(u64 pfn, u64 nr_pages);
int __pkvm_host_unshare_ffa(u64 pfn, u64 nr_pages);
+int __pkvm_host_donate_guest(u64 pfn, u64 gfn, struct pkvm_hyp_vcpu *vcpu);
int __pkvm_host_share_guest(u64 pfn, u64 gfn, u64 nr_pages, struct pkvm_hyp_vcpu *vcpu,
enum kvm_pgtable_prot prot);
int __pkvm_host_unshare_guest(u64 gfn, u64 nr_pages, struct pkvm_hyp_vm *hyp_vm);
diff --git a/arch/arm64/kvm/hyp/nvhe/hyp-main.c b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
index 634ea2766240..970656318cf2 100644
--- a/arch/arm64/kvm/hyp/nvhe/hyp-main.c
+++ b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
@@ -241,6 +241,26 @@ static int pkvm_refill_memcache(struct pkvm_hyp_vcpu *hyp_vcpu)
&host_vcpu->arch.pkvm_memcache);
}

+static void handle___pkvm_host_donate_guest(struct kvm_cpu_context *host_ctxt)
+{
+ DECLARE_REG(u64, pfn, host_ctxt, 1);
+ DECLARE_REG(u64, gfn, host_ctxt, 2);
+ struct pkvm_hyp_vcpu *hyp_vcpu;
+ int ret = -EINVAL;
+
+ hyp_vcpu = pkvm_get_loaded_hyp_vcpu();
+ if (!hyp_vcpu || !pkvm_hyp_vcpu_is_protected(hyp_vcpu))
+ goto out;
+
+ ret = pkvm_refill_memcache(hyp_vcpu);
+ if (ret)
+ goto out;
+
+ ret = __pkvm_host_donate_guest(pfn, gfn, hyp_vcpu);
+out:
+ cpu_reg(host_ctxt, 1) = ret;
+}
+
static void handle___pkvm_host_share_guest(struct kvm_cpu_context *host_ctxt)
{
DECLARE_REG(u64, pfn, host_ctxt, 1);
@@ -595,6 +615,7 @@ static const hcall_t host_hcall[] = {

HANDLE_FUNC(__pkvm_host_share_hyp),
HANDLE_FUNC(__pkvm_host_unshare_hyp),
+ HANDLE_FUNC(__pkvm_host_donate_guest),
HANDLE_FUNC(__pkvm_host_share_guest),
HANDLE_FUNC(__pkvm_host_unshare_guest),
HANDLE_FUNC(__pkvm_host_relax_perms_guest),
diff --git a/arch/arm64/kvm/hyp/nvhe/mem_protect.c b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
index 7d22893ab1dc..03e6fa124253 100644
--- a/arch/arm64/kvm/hyp/nvhe/mem_protect.c
+++ b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
@@ -971,6 +971,36 @@ static int __guest_check_transition_size(u64 phys, u64 ipa, u64 nr_pages, u64 *s
return 0;
}

+int __pkvm_host_donate_guest(u64 pfn, u64 gfn, struct pkvm_hyp_vcpu *vcpu)
+{
+ struct pkvm_hyp_vm *vm = pkvm_hyp_vcpu_to_hyp_vm(vcpu);
+ u64 phys = hyp_pfn_to_phys(pfn);
+ u64 ipa = hyp_pfn_to_phys(gfn);
+ int ret;
+
+ host_lock_component();
+ guest_lock_component(vm);
+
+ ret = __host_check_page_state_range(phys, PAGE_SIZE, PKVM_PAGE_OWNED);
+ if (ret)
+ goto unlock;
+
+ ret = __guest_check_page_state_range(vm, ipa, PAGE_SIZE, PKVM_NOPAGE);
+ if (ret)
+ goto unlock;
+
+ WARN_ON(host_stage2_set_owner_locked(phys, PAGE_SIZE, PKVM_ID_GUEST));
+ WARN_ON(kvm_pgtable_stage2_map(&vm->pgt, ipa, PAGE_SIZE, phys,
+ pkvm_mkstate(KVM_PGTABLE_PROT_RWX, PKVM_PAGE_OWNED),
+ &vcpu->vcpu.arch.pkvm_memcache, 0));
+
+unlock:
+ guest_unlock_component(vm);
+ host_unlock_component();
+
+ return ret;
+}
+
int __pkvm_host_share_guest(u64 pfn, u64 gfn, u64 nr_pages, struct pkvm_hyp_vcpu *vcpu,
enum kvm_pgtable_prot prot)
{
--
2.53.0.1018.g2bb0e51243-goog