[PATCH 11/18] KVM: arm64: Introduce __pkvm_host_unshare_guest()

[Quentin Perret <qperret@google.com>]

In preparation for letting the host unmap pages from non-protected
guests, introduce a new hypercall implementing the host-unshare-guest
transition.

Signed-off-by: Quentin Perret <qperret@google.com>
---
 arch/arm64/include/asm/kvm_asm.h              |  1 +
 arch/arm64/kvm/hyp/include/nvhe/mem_protect.h |  1 +
 arch/arm64/kvm/hyp/include/nvhe/pkvm.h        |  5 ++
 arch/arm64/kvm/hyp/nvhe/hyp-main.c            | 24 ++++++
 arch/arm64/kvm/hyp/nvhe/mem_protect.c         | 78 +++++++++++++++++++
 5 files changed, 109 insertions(+)

diff --git a/arch/arm64/include/asm/kvm_asm.h b/arch/arm64/include/asm/kvm_asm.h
index b69390108c5a..e67efee936b6 100644
--- a/arch/arm64/include/asm/kvm_asm.h
+++ b/arch/arm64/include/asm/kvm_asm.h
@@ -66,6 +66,7 @@ enum __kvm_host_smccc_func {
 	__KVM_HOST_SMCCC_FUNC___pkvm_host_share_hyp,
 	__KVM_HOST_SMCCC_FUNC___pkvm_host_unshare_hyp,
 	__KVM_HOST_SMCCC_FUNC___pkvm_host_share_guest,
+	__KVM_HOST_SMCCC_FUNC___pkvm_host_unshare_guest,
 	__KVM_HOST_SMCCC_FUNC___kvm_adjust_pc,
 	__KVM_HOST_SMCCC_FUNC___kvm_vcpu_run,
 	__KVM_HOST_SMCCC_FUNC___kvm_flush_vm_context,
diff --git a/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h b/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h
index a7976e50f556..e528a42ed60e 100644
--- a/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h
+++ b/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h
@@ -40,6 +40,7 @@ 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_share_guest(u64 pfn, u64 gfn, struct pkvm_hyp_vcpu *vcpu, enum kvm_pgtable_prot prot);
+int __pkvm_host_unshare_guest(u64 gfn, struct pkvm_hyp_vm *hyp_vm);
 
 bool addr_is_memory(phys_addr_t phys);
 int host_stage2_idmap_locked(phys_addr_t addr, u64 size, enum kvm_pgtable_prot prot);
diff --git a/arch/arm64/kvm/hyp/include/nvhe/pkvm.h b/arch/arm64/kvm/hyp/include/nvhe/pkvm.h
index be52c5b15e21..5dfc9ece9aa5 100644
--- a/arch/arm64/kvm/hyp/include/nvhe/pkvm.h
+++ b/arch/arm64/kvm/hyp/include/nvhe/pkvm.h
@@ -64,6 +64,11 @@ static inline bool pkvm_hyp_vcpu_is_protected(struct pkvm_hyp_vcpu *hyp_vcpu)
 	return vcpu_is_protected(&hyp_vcpu->vcpu);
 }
 
+static inline bool pkvm_hyp_vm_is_protected(struct pkvm_hyp_vm *hyp_vm)
+{
+	return kvm_vm_is_protected(&hyp_vm->kvm);
+}
+
 void pkvm_hyp_vm_table_init(void *tbl);
 
 int __pkvm_init_vm(struct kvm *host_kvm, unsigned long vm_hva,
diff --git a/arch/arm64/kvm/hyp/nvhe/hyp-main.c b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
index 32bdf6b27958..68bbef69d99a 100644
--- a/arch/arm64/kvm/hyp/nvhe/hyp-main.c
+++ b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
@@ -242,6 +242,29 @@ static void handle___pkvm_host_share_guest(struct kvm_cpu_context *host_ctxt)
 	cpu_reg(host_ctxt, 1) =  ret;
 }
 
+static void handle___pkvm_host_unshare_guest(struct kvm_cpu_context *host_ctxt)
+{
+	DECLARE_REG(pkvm_handle_t, handle, host_ctxt, 1);
+	DECLARE_REG(u64, gfn, host_ctxt, 2);
+	struct pkvm_hyp_vm *hyp_vm;
+	int ret = -EINVAL;
+
+	if (!is_protected_kvm_enabled())
+		goto out;
+
+	hyp_vm = get_pkvm_hyp_vm(handle);
+	if (!hyp_vm)
+		goto out;
+	if (pkvm_hyp_vm_is_protected(hyp_vm))
+		goto put_hyp_vm;
+
+	ret = __pkvm_host_unshare_guest(gfn, hyp_vm);
+put_hyp_vm:
+	put_pkvm_hyp_vm(hyp_vm);
+out:
+	cpu_reg(host_ctxt, 1) =  ret;
+}
+
 static void handle___kvm_adjust_pc(struct kvm_cpu_context *host_ctxt)
 {
 	DECLARE_REG(struct kvm_vcpu *, vcpu, host_ctxt, 1);
@@ -459,6 +482,7 @@ static const hcall_t host_hcall[] = {
 	HANDLE_FUNC(__pkvm_host_share_hyp),
 	HANDLE_FUNC(__pkvm_host_unshare_hyp),
 	HANDLE_FUNC(__pkvm_host_share_guest),
+	HANDLE_FUNC(__pkvm_host_unshare_guest),
 	HANDLE_FUNC(__kvm_adjust_pc),
 	HANDLE_FUNC(__kvm_vcpu_run),
 	HANDLE_FUNC(__kvm_flush_vm_context),
diff --git a/arch/arm64/kvm/hyp/nvhe/mem_protect.c b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
index a69d7212b64c..f7476a29e1a9 100644
--- a/arch/arm64/kvm/hyp/nvhe/mem_protect.c
+++ b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
@@ -1413,3 +1413,81 @@ int __pkvm_host_share_guest(u64 pfn, u64 gfn, struct pkvm_hyp_vcpu *vcpu,
 
 	return ret;
 }
+
+static int guest_get_valid_pte(struct pkvm_hyp_vm *vm, u64 *phys, u64 ipa, u8 order, kvm_pte_t *pte)
+{
+	size_t size = PAGE_SIZE << order;
+	s8 level;
+
+	if (order && size != PMD_SIZE)
+		return -EINVAL;
+
+	WARN_ON(kvm_pgtable_get_leaf(&vm->pgt, ipa, pte, &level));
+
+	if (kvm_granule_size(level) != size)
+		return -E2BIG;
+
+	if (!kvm_pte_valid(*pte))
+		return -ENOENT;
+
+	*phys = kvm_pte_to_phys(*pte);
+
+	return 0;
+}
+
+static int __check_host_unshare_guest(struct pkvm_hyp_vm *vm, u64 *phys, u64 ipa)
+{
+	enum pkvm_page_state state;
+	struct hyp_page *page;
+	kvm_pte_t pte;
+	int ret;
+
+	ret = guest_get_valid_pte(vm, phys, ipa, 0, &pte);
+	if (ret)
+		return ret;
+
+	state = guest_get_page_state(pte, ipa);
+	if (state != PKVM_PAGE_SHARED_BORROWED)
+		return -EPERM;
+
+	ret = range_is_allowed_memory(*phys, *phys + PAGE_SIZE);
+	if (ret)
+		return ret;
+
+	page = hyp_phys_to_page(*phys);
+	if (page->host_state != PKVM_PAGE_SHARED_OWNED)
+		return -EPERM;
+	WARN_ON(!page->host_share_guest_count);
+
+	return 0;
+}
+
+int __pkvm_host_unshare_guest(u64 gfn, struct pkvm_hyp_vm *hyp_vm)
+{
+	u64 ipa = hyp_pfn_to_phys(gfn);
+	struct hyp_page *page;
+	u64 phys;
+	int ret;
+
+	host_lock_component();
+	guest_lock_component(hyp_vm);
+
+	ret = __check_host_unshare_guest(hyp_vm, &phys, ipa);
+	if (ret)
+		goto unlock;
+
+	ret = kvm_pgtable_stage2_unmap(&hyp_vm->pgt, ipa, PAGE_SIZE);
+	if (ret)
+		goto unlock;
+
+	page = hyp_phys_to_page(phys);
+	page->host_share_guest_count--;
+	if (!page->host_share_guest_count)
+		WARN_ON(__host_set_page_state_range(phys, PAGE_SIZE, PKVM_PAGE_OWNED));
+
+unlock:
+	guest_unlock_component(hyp_vm);
+	host_unlock_component();
+
+	return ret;
+}
-- 
2.47.0.163.g1226f6d8fa-goog