[PATCH v3 29/36] KVM: arm64: Implement the MEM_UNSHARE hypercall for protected VMs

Will Deacon
2026-03-05T14:45:51Z

Implement the ARM_SMCCC_KVM_FUNC_MEM_UNSHARE hypercall to allow
protected VMs to unshare memory that was previously shared with the host
using the ARM_SMCCC_KVM_FUNC_MEM_SHARE hypercall.

Reviewed-by: Vincent Donnefort <vdonnefort@google.com>
Signed-off-by: Will Deacon <will@kernel.org>
---
arch/arm64/kvm/hyp/include/nvhe/mem_protect.h | 1 +
arch/arm64/kvm/hyp/nvhe/mem_protect.c | 34 +++++++++++++++++++
arch/arm64/kvm/hyp/nvhe/pkvm.c | 22 ++++++++++++
3 files changed, 57 insertions(+)

diff --git a/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h b/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h
index 42fd60c5cfc9..e41a128b0854 100644
--- a/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h
+++ b/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h
@@ -36,6 +36,7 @@ extern unsigned long hyp_nr_cpus;
int __pkvm_prot_finalize(void);
int __pkvm_host_share_hyp(u64 pfn);
int __pkvm_guest_share_host(struct pkvm_hyp_vcpu *vcpu, u64 gfn);
+int __pkvm_guest_unshare_host(struct pkvm_hyp_vcpu *vcpu, u64 gfn);
int __pkvm_host_unshare_hyp(u64 pfn);
int __pkvm_host_donate_hyp(u64 pfn, u64 nr_pages);
int __pkvm_hyp_donate_host(u64 pfn, u64 nr_pages);
diff --git a/arch/arm64/kvm/hyp/nvhe/mem_protect.c b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
index 22d456ab15a6..4451955ac767 100644
--- a/arch/arm64/kvm/hyp/nvhe/mem_protect.c
+++ b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
@@ -991,6 +991,40 @@ int __pkvm_guest_share_host(struct pkvm_hyp_vcpu *vcpu, u64 gfn)
return ret;
}

+int __pkvm_guest_unshare_host(struct pkvm_hyp_vcpu *vcpu, u64 gfn)
+{
+ struct pkvm_hyp_vm *vm = pkvm_hyp_vcpu_to_hyp_vm(vcpu);
+ u64 meta, phys, ipa = hyp_pfn_to_phys(gfn);
+ kvm_pte_t pte;
+ int ret;
+
+ host_lock_component();
+ guest_lock_component(vm);
+
+ ret = get_valid_guest_pte(vm, ipa, &pte, &phys);
+ if (ret)
+ goto unlock;
+
+ ret = -EPERM;
+ if (pkvm_getstate(kvm_pgtable_stage2_pte_prot(pte)) != PKVM_PAGE_SHARED_OWNED)
+ goto unlock;
+ if (__host_check_page_state_range(phys, PAGE_SIZE, PKVM_PAGE_SHARED_BORROWED))
+ goto unlock;
+
+ ret = 0;
+ meta = host_stage2_encode_gfn_meta(vm, gfn);
+ WARN_ON(host_stage2_set_owner_metadata_locked(phys, PAGE_SIZE,
+ PKVM_ID_GUEST, meta));
+ 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_unshare_hyp(u64 pfn)
{
u64 phys = hyp_pfn_to_phys(pfn);
diff --git a/arch/arm64/kvm/hyp/nvhe/pkvm.c b/arch/arm64/kvm/hyp/nvhe/pkvm.c
index 1dc9225073c4..ebfd9904ede6 100644
--- a/arch/arm64/kvm/hyp/nvhe/pkvm.c
+++ b/arch/arm64/kvm/hyp/nvhe/pkvm.c
@@ -1019,6 +1019,19 @@ static bool pkvm_memshare_call(u64 *ret, struct kvm_vcpu *vcpu, u64 *exit_code)
return false;
}

+static void pkvm_memunshare_call(u64 *ret, struct kvm_vcpu *vcpu)
+{
+ struct pkvm_hyp_vcpu *hyp_vcpu;
+ u64 ipa = smccc_get_arg1(vcpu);
+
+ if (!PAGE_ALIGNED(ipa))
+ return;
+
+ hyp_vcpu = container_of(vcpu, struct pkvm_hyp_vcpu, vcpu);
+ if (!__pkvm_guest_unshare_host(hyp_vcpu, hyp_phys_to_pfn(ipa)))
+ ret[0] = SMCCC_RET_SUCCESS;
+}
+
/*
* Handler for protected VM HVC calls.
*
@@ -1036,6 +1049,7 @@ bool kvm_handle_pvm_hvc64(struct kvm_vcpu *vcpu, u64 *exit_code)
val[0] = BIT(ARM_SMCCC_KVM_FUNC_FEATURES);
val[0] |= BIT(ARM_SMCCC_KVM_FUNC_HYP_MEMINFO);
val[0] |= BIT(ARM_SMCCC_KVM_FUNC_MEM_SHARE);
+ val[0] |= BIT(ARM_SMCCC_KVM_FUNC_MEM_UNSHARE);
break;
case ARM_SMCCC_VENDOR_HYP_KVM_HYP_MEMINFO_FUNC_ID:
if (smccc_get_arg1(vcpu) ||
@@ -1054,6 +1068,14 @@ bool kvm_handle_pvm_hvc64(struct kvm_vcpu *vcpu, u64 *exit_code)

handled = pkvm_memshare_call(val, vcpu, exit_code);
break;
+ case ARM_SMCCC_VENDOR_HYP_KVM_MEM_UNSHARE_FUNC_ID:
+ if (smccc_get_arg2(vcpu) ||
+ smccc_get_arg3(vcpu)) {
+ break;
+ }
+
+ pkvm_memunshare_call(val, vcpu);
+ break;
default:
/* Punt everything else back to the host, for now. */
handled = false;
--
2.53.0.473.g4a7958ca14-goog