[PATCH 25/30] KVM: arm64: Implement the MEM_UNSHARE hypercall for protected VMs

[Will Deacon]

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.

Signed-off-by: Will Deacon <will at kernel.org>
---
 arch/arm64/kvm/hyp/include/nvhe/mem_protect.h |  1 +
 arch/arm64/kvm/hyp/nvhe/mem_protect.c         | 32 +++++++++++++++++++
 arch/arm64/kvm/hyp/nvhe/pkvm.c                | 22 +++++++++++++
 3 files changed, 55 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 365c769c82a4..c1600b88c316 100644
--- a/arch/arm64/kvm/hyp/nvhe/mem_protect.c
+++ b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
@@ -920,6 +920,38 @@ 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 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;
+	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_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 d8afa2b98542..2890328f4a78 100644
--- a/arch/arm64/kvm/hyp/nvhe/pkvm.c
+++ b/arch/arm64/kvm/hyp/nvhe/pkvm.c
@@ -988,6 +988,19 @@ 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.
  *
@@ -1005,6 +1018,7 @@ 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) ||
@@ -1023,6 +1037,14 @@ 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;
-- 
2.52.0.351.gbe84eed79e-goog