[PATCH v2 15/35] KVM: arm64: Introduce __pkvm_reclaim_dying_guest_page()

Will Deacon
2026-01-19T12:47:39Z

To enable reclaim of pages from a protected VM during teardown,
introduce a new hypercall to reclaim a single page from a protected
guest that is in the dying state.

Since the EL2 code is non-preemptible, the new hypercall deliberately
acts on a single page at a time so as to allow EL1 to reschedule
frequently during the teardown operation.

Reviewed-by: Vincent Donnefort <vdonnefort@google.com>
Co-developed-by: Quentin Perret <qperret@google.com>
Signed-off-by: Quentin Perret <qperret@google.com>
Signed-off-by: Will Deacon <will@kernel.org>
---
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 | 1 +
arch/arm64/kvm/hyp/nvhe/hyp-main.c | 9 +++
arch/arm64/kvm/hyp/nvhe/mem_protect.c | 79 +++++++++++++++++++
arch/arm64/kvm/hyp/nvhe/pkvm.c | 14 ++++
6 files changed, 105 insertions(+)

diff --git a/arch/arm64/include/asm/kvm_asm.h b/arch/arm64/include/asm/kvm_asm.h
index 2750b75b5b8f..2e7e8e7771f6 100644
--- a/arch/arm64/include/asm/kvm_asm.h
+++ b/arch/arm64/include/asm/kvm_asm.h
@@ -90,6 +90,7 @@ enum __kvm_host_smccc_func {
__KVM_HOST_SMCCC_FUNC___pkvm_unreserve_vm,
__KVM_HOST_SMCCC_FUNC___pkvm_init_vm,
__KVM_HOST_SMCCC_FUNC___pkvm_init_vcpu,
+ __KVM_HOST_SMCCC_FUNC___pkvm_reclaim_dying_guest_page,
__KVM_HOST_SMCCC_FUNC___pkvm_start_teardown_vm,
__KVM_HOST_SMCCC_FUNC___pkvm_finalize_teardown_vm,
__KVM_HOST_SMCCC_FUNC___pkvm_vcpu_load,
diff --git a/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h b/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h
index 9c0cc53d1dc9..cde38a556049 100644
--- a/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h
+++ b/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h
@@ -41,6 +41,7 @@ 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_donate_guest(u64 pfn, u64 gfn, struct pkvm_hyp_vcpu *vcpu);
+int __pkvm_host_reclaim_page_guest(u64 gfn, struct pkvm_hyp_vm *vm);
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/include/nvhe/pkvm.h b/arch/arm64/kvm/hyp/include/nvhe/pkvm.h
index 04c7ca703014..506831804f64 100644
--- a/arch/arm64/kvm/hyp/include/nvhe/pkvm.h
+++ b/arch/arm64/kvm/hyp/include/nvhe/pkvm.h
@@ -74,6 +74,7 @@ int __pkvm_init_vm(struct kvm *host_kvm, unsigned long vm_hva,
int __pkvm_init_vcpu(pkvm_handle_t handle, struct kvm_vcpu *host_vcpu,
unsigned long vcpu_hva);

+int __pkvm_reclaim_dying_guest_page(pkvm_handle_t handle, u64 gfn);
int __pkvm_start_teardown_vm(pkvm_handle_t handle);
int __pkvm_finalize_teardown_vm(pkvm_handle_t handle);

diff --git a/arch/arm64/kvm/hyp/nvhe/hyp-main.c b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
index c04300b51c9a..f43c50ae2d81 100644
--- a/arch/arm64/kvm/hyp/nvhe/hyp-main.c
+++ b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
@@ -570,6 +570,14 @@ static void handle___pkvm_init_vcpu(struct kvm_cpu_context *host_ctxt)
cpu_reg(host_ctxt, 1) = __pkvm_init_vcpu(handle, host_vcpu, vcpu_hva);
}

+static void handle___pkvm_reclaim_dying_guest_page(struct kvm_cpu_context *host_ctxt)
+{
+ DECLARE_REG(pkvm_handle_t, handle, host_ctxt, 1);
+ DECLARE_REG(u64, gfn, host_ctxt, 2);
+
+ cpu_reg(host_ctxt, 1) = __pkvm_reclaim_dying_guest_page(handle, gfn);
+}
+
static void handle___pkvm_start_teardown_vm(struct kvm_cpu_context *host_ctxt)
{
DECLARE_REG(pkvm_handle_t, handle, host_ctxt, 1);
@@ -623,6 +631,7 @@ static const hcall_t host_hcall[] = {
HANDLE_FUNC(__pkvm_unreserve_vm),
HANDLE_FUNC(__pkvm_init_vm),
HANDLE_FUNC(__pkvm_init_vcpu),
+ HANDLE_FUNC(__pkvm_reclaim_dying_guest_page),
HANDLE_FUNC(__pkvm_start_teardown_vm),
HANDLE_FUNC(__pkvm_finalize_teardown_vm),
HANDLE_FUNC(__pkvm_vcpu_load),
diff --git a/arch/arm64/kvm/hyp/nvhe/mem_protect.c b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
index f24e8ce2c40c..ef21e8e7a734 100644
--- a/arch/arm64/kvm/hyp/nvhe/mem_protect.c
+++ b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
@@ -736,6 +736,32 @@ static int __guest_check_page_state_range(struct pkvm_hyp_vm *vm, u64 addr,
return check_page_state_range(&vm->pgt, addr, size, &d);
}

+static int get_valid_guest_pte(struct pkvm_hyp_vm *vm, u64 ipa, kvm_pte_t *ptep, u64 *physp)
+{
+ kvm_pte_t pte;
+ u64 phys;
+ s8 level;
+ int ret;
+
+ ret = kvm_pgtable_get_leaf(&vm->pgt, ipa, &pte, &level);
+ if (ret)
+ return ret;
+ if (!kvm_pte_valid(pte))
+ return -ENOENT;
+ if (level != KVM_PGTABLE_LAST_LEVEL)
+ return -E2BIG;
+
+ phys = kvm_pte_to_phys(pte);
+ ret = check_range_allowed_memory(phys, phys + PAGE_SIZE);
+ if (WARN_ON(ret))
+ return ret;
+
+ *ptep = pte;
+ *physp = phys;
+
+ return 0;
+}
+
int __pkvm_host_share_hyp(u64 pfn)
{
u64 phys = hyp_pfn_to_phys(pfn);
@@ -969,6 +995,59 @@ static int __guest_check_transition_size(u64 phys, u64 ipa, u64 nr_pages, u64 *s
return 0;
}

+static void hyp_poison_page(phys_addr_t phys)
+{
+ void *addr = hyp_fixmap_map(phys);
+
+ memset(addr, 0, PAGE_SIZE);
+ /*
+ * Prefer kvm_flush_dcache_to_poc() over __clean_dcache_guest_page()
+ * here as the latter may elide the CMO under the assumption that FWB
+ * will be enabled on CPUs that support it. This is incorrect for the
+ * host stage-2 and would otherwise lead to a malicious host potentially
+ * being able to read the contents of newly reclaimed guest pages.
+ */
+ kvm_flush_dcache_to_poc(addr, PAGE_SIZE);
+ hyp_fixmap_unmap();
+}
+
+int __pkvm_host_reclaim_page_guest(u64 gfn, struct pkvm_hyp_vm *vm)
+{
+ u64 ipa = hyp_pfn_to_phys(gfn);
+ kvm_pte_t pte;
+ u64 phys;
+ int ret;
+
+ host_lock_component();
+ guest_lock_component(vm);
+
+ ret = get_valid_guest_pte(vm, ipa, &pte, &phys);
+ if (ret)
+ goto unlock;
+
+ switch (guest_get_page_state(pte, ipa)) {
+ case PKVM_PAGE_OWNED:
+ WARN_ON(__host_check_page_state_range(phys, PAGE_SIZE, PKVM_NOPAGE));
+ hyp_poison_page(phys);
+ break;
+ case PKVM_PAGE_SHARED_OWNED:
+ WARN_ON(__host_check_page_state_range(phys, PAGE_SIZE, PKVM_PAGE_SHARED_BORROWED));
+ break;
+ default:
+ ret = -EPERM;
+ goto unlock;
+ }
+
+ WARN_ON(kvm_pgtable_stage2_unmap(&vm->pgt, ipa, PAGE_SIZE));
+ WARN_ON(host_stage2_set_owner_locked(phys, PAGE_SIZE, PKVM_ID_HOST));
+
+unlock:
+ guest_unlock_component(vm);
+ host_unlock_component();
+
+ return ret;
+}
+
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);
diff --git a/arch/arm64/kvm/hyp/nvhe/pkvm.c b/arch/arm64/kvm/hyp/nvhe/pkvm.c
index 7f8191f96fc3..9f0997150cf5 100644
--- a/arch/arm64/kvm/hyp/nvhe/pkvm.c
+++ b/arch/arm64/kvm/hyp/nvhe/pkvm.c
@@ -832,6 +832,20 @@ teardown_donated_memory(struct kvm_hyp_memcache *mc, void *addr, size_t size)
unmap_donated_memory_noclear(addr, size);
}

+int __pkvm_reclaim_dying_guest_page(pkvm_handle_t handle, u64 gfn)
+{
+ struct pkvm_hyp_vm *hyp_vm;
+ int ret = -EINVAL;
+
+ hyp_spin_lock(&vm_table_lock);
+ hyp_vm = get_vm_by_handle(handle);
+ if (hyp_vm && hyp_vm->kvm.arch.pkvm.is_dying)
+ ret = __pkvm_host_reclaim_page_guest(gfn, hyp_vm);
+ hyp_spin_unlock(&vm_table_lock);
+
+ return ret;
+}
+
int __pkvm_start_teardown_vm(pkvm_handle_t handle)
{
struct pkvm_hyp_vm *hyp_vm;
--
2.52.0.457.g6b5491de43-goog