[PATCH v7 21/45] arm64: RME: Runtime faulting of memory

Steven Price
2025-02-13T16:16:17Z

At runtime if the realm guest accesses memory which hasn't yet been
mapped then KVM needs to either populate the region or fault the guest.

For memory in the lower (protected) region of IPA a fresh page is
provided to the RMM which will zero the contents. For memory in the
upper (shared) region of IPA, the memory from the memslot is mapped
into the realm VM non secure.

Signed-off-by: Steven Price <steven.price@arm.com>
---
Changes since v6:
* Handle PAGE_SIZE being larger than RMM granule size.
* Some minor renaming following review comments.
Changes since v5:
* Reduce use of struct page in preparation for supporting the RMM
having a different page size to the host.
* Handle a race when delegating a page where another CPU has faulted on
a the same page (and already delegated the physical page) but not yet
mapped it. In this case simply return to the guest to either use the
mapping from the other CPU (or refault if the race is lost).
* The changes to populate_par_region() are moved into the previous
patch where they belong.
Changes since v4:
* Code cleanup following review feedback.
* Drop the PTE_SHARED bit when creating unprotected page table entries.
This is now set by the RMM and the host has no control of it and the
spec requires the bit to be set to zero.
Changes since v2:
* Avoid leaking memory if failing to map it in the realm.
* Correctly mask RTT based on LPA2 flag (see rtt_get_phys()).
* Adapt to changes in previous patches.
---
arch/arm64/include/asm/kvm_emulate.h | 10 ++
arch/arm64/include/asm/kvm_rme.h | 10 ++
arch/arm64/kvm/mmu.c | 127 ++++++++++++++++++-
arch/arm64/kvm/rme.c | 176 +++++++++++++++++++++++++++
4 files changed, 317 insertions(+), 6 deletions(-)

diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h
index f7b5a78f2e91..a74c0751504e 100644
--- a/arch/arm64/include/asm/kvm_emulate.h
+++ b/arch/arm64/include/asm/kvm_emulate.h
@@ -709,6 +709,16 @@ static inline bool kvm_realm_is_created(struct kvm *kvm)
return kvm_is_realm(kvm) && kvm_realm_state(kvm) != REALM_STATE_NONE;
}

+static inline gpa_t kvm_gpa_from_fault(struct kvm *kvm, phys_addr_t ipa)
+{
+ if (kvm_is_realm(kvm)) {
+ struct realm *realm = &kvm->arch.realm;
+
+ return ipa & ~BIT(realm->ia_bits - 1);
+ }
+ return ipa;
+}
+
static inline bool vcpu_is_rec(struct kvm_vcpu *vcpu)
{
if (static_branch_unlikely(&kvm_rme_is_available))
diff --git a/arch/arm64/include/asm/kvm_rme.h b/arch/arm64/include/asm/kvm_rme.h
index a7c519b19e57..945927c70746 100644
--- a/arch/arm64/include/asm/kvm_rme.h
+++ b/arch/arm64/include/asm/kvm_rme.h
@@ -99,6 +99,16 @@ void kvm_realm_unmap_range(struct kvm *kvm,
unsigned long ipa,
u64 size,
bool unmap_private);
+int realm_map_protected(struct realm *realm,
+ unsigned long base_ipa,
+ kvm_pfn_t pfn,
+ unsigned long size,
+ struct kvm_mmu_memory_cache *memcache);
+int realm_map_non_secure(struct realm *realm,
+ unsigned long ipa,
+ kvm_pfn_t pfn,
+ unsigned long size,
+ struct kvm_mmu_memory_cache *memcache);

static inline bool kvm_realm_is_private_address(struct realm *realm,
unsigned long addr)
diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index 24eb60063573..994e71cfb358 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -338,8 +338,13 @@ static void __unmap_stage2_range(struct kvm_s2_mmu *mmu, phys_addr_t start, u64

lockdep_assert_held_write(&kvm->mmu_lock);
WARN_ON(size & ~PAGE_MASK);
- WARN_ON(stage2_apply_range(mmu, start, end, KVM_PGT_FN(kvm_pgtable_stage2_unmap),
- may_block));
+
+ if (kvm_is_realm(kvm))
+ kvm_realm_unmap_range(kvm, start, size, !only_shared);
+ else
+ WARN_ON(stage2_apply_range(mmu, start, end,
+ KVM_PGT_FN(kvm_pgtable_stage2_unmap),
+ may_block));
}

void kvm_stage2_unmap_range(struct kvm_s2_mmu *mmu, phys_addr_t start,
@@ -359,7 +364,10 @@ static void stage2_flush_memslot(struct kvm *kvm,
phys_addr_t addr = memslot->base_gfn << PAGE_SHIFT;
phys_addr_t end = addr + PAGE_SIZE * memslot->npages;

- kvm_stage2_flush_range(&kvm->arch.mmu, addr, end);
+ if (kvm_is_realm(kvm))
+ kvm_realm_unmap_range(kvm, addr, end - addr, false);
+ else
+ kvm_stage2_flush_range(&kvm->arch.mmu, addr, end);
}

/**
@@ -1053,6 +1061,10 @@ void stage2_unmap_vm(struct kvm *kvm)
struct kvm_memory_slot *memslot;
int idx, bkt;

+ /* For realms this is handled by the RMM so nothing to do here */
+ if (kvm_is_realm(kvm))
+ return;
+
idx = srcu_read_lock(&kvm->srcu);
mmap_read_lock(current->mm);
write_lock(&kvm->mmu_lock);
@@ -1078,6 +1090,7 @@ void kvm_free_stage2_pgd(struct kvm_s2_mmu *mmu)
if (kvm_is_realm(kvm) &&
(kvm_realm_state(kvm) != REALM_STATE_DEAD &&
kvm_realm_state(kvm) != REALM_STATE_NONE)) {
+ kvm_stage2_unmap_range(mmu, 0, (~0ULL) & PAGE_MASK, false);
write_unlock(&kvm->mmu_lock);
kvm_realm_destroy_rtts(kvm, pgt->ia_bits);

@@ -1470,6 +1483,82 @@ static bool kvm_vma_mte_allowed(struct vm_area_struct *vma)
return vma->vm_flags & VM_MTE_ALLOWED;
}

+static int realm_map_ipa(struct kvm *kvm, phys_addr_t ipa,
+ kvm_pfn_t pfn, unsigned long map_size,
+ enum kvm_pgtable_prot prot,
+ struct kvm_mmu_memory_cache *memcache)
+{
+ struct realm *realm = &kvm->arch.realm;
+
+ if (WARN_ON(!(prot & KVM_PGTABLE_PROT_W)))
+ return -EFAULT;
+
+ ipa = ALIGN_DOWN(ipa, PAGE_SIZE);
+
+ if (!kvm_realm_is_private_address(realm, ipa))
+ return realm_map_non_secure(realm, ipa, pfn, map_size,
+ memcache);
+
+ return realm_map_protected(realm, ipa, pfn, map_size, memcache);
+}
+
+static int private_memslot_fault(struct kvm_vcpu *vcpu,
+ phys_addr_t fault_ipa,
+ struct kvm_memory_slot *memslot)
+{
+ struct kvm *kvm = vcpu->kvm;
+ gpa_t gpa = kvm_gpa_from_fault(kvm, fault_ipa);
+ gfn_t gfn = gpa >> PAGE_SHIFT;
+ bool is_priv_gfn = kvm_mem_is_private(kvm, gfn);
+ struct kvm_mmu_memory_cache *memcache = &vcpu->arch.mmu_page_cache;
+ struct page *page;
+ kvm_pfn_t pfn;
+ int ret;
+ /*
+ * For Realms, the shared address is an alias of the private GPA with
+ * the top bit set. Thus is the fault address matches the GPA then it
+ * is the private alias.
+ */
+ bool is_priv_fault = (gpa == fault_ipa);
+
+ if (is_priv_gfn != is_priv_fault) {
+ kvm_prepare_memory_fault_exit(vcpu,
+ gpa,
+ PAGE_SIZE,
+ kvm_is_write_fault(vcpu),
+ false, is_priv_fault);
+
+ /*
+ * KVM_EXIT_MEMORY_FAULT requires an return code of -EFAULT,
+ * see the API documentation
+ */
+ return -EFAULT;
+ }
+
+ if (!is_priv_fault) {
+ /* Not a private mapping, handling normally */
+ return -EINVAL;
+ }
+
+ ret = kvm_mmu_topup_memory_cache(memcache,
+ kvm_mmu_cache_min_pages(vcpu->arch.hw_mmu));
+ if (ret)
+ return ret;
+
+ ret = kvm_gmem_get_pfn(kvm, memslot, gfn, &pfn, &page, NULL);
+ if (ret)
+ return ret;
+
+ /* FIXME: Should be able to use bigger than PAGE_SIZE mappings */
+ ret = realm_map_ipa(kvm, fault_ipa, pfn, PAGE_SIZE, KVM_PGTABLE_PROT_W,
+ memcache);
+ if (!ret)
+ return 1; /* Handled */
+
+ put_page(page);
+ return ret;
+}
+
static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
struct kvm_s2_trans *nested,
struct kvm_memory_slot *memslot, unsigned long hva,
@@ -1497,6 +1586,14 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
if (fault_is_perm)
fault_granule = kvm_vcpu_trap_get_perm_fault_granule(vcpu);
write_fault = kvm_is_write_fault(vcpu);
+
+ /*
+ * Realms cannot map protected pages read-only
+ * FIXME: It should be possible to map unprotected pages read-only
+ */
+ if (vcpu_is_rec(vcpu))
+ write_fault = true;
+
exec_fault = kvm_vcpu_trap_is_exec_fault(vcpu);
VM_BUG_ON(write_fault && exec_fault);

@@ -1611,7 +1708,7 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
ipa &= ~(vma_pagesize - 1);
}

- gfn = ipa >> PAGE_SHIFT;
+ gfn = kvm_gpa_from_fault(kvm, ipa) >> PAGE_SHIFT;
mte_allowed = kvm_vma_mte_allowed(vma);

vfio_allow_any_uc = vma->vm_flags & VM_ALLOW_ANY_UNCACHED;
@@ -1744,6 +1841,9 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
*/
prot &= ~KVM_NV_GUEST_MAP_SZ;
ret = KVM_PGT_FN(kvm_pgtable_stage2_relax_perms)(pgt, fault_ipa, prot, flags);
+ } else if (kvm_is_realm(kvm)) {
+ ret = realm_map_ipa(kvm, fault_ipa, pfn, vma_pagesize,
+ prot, memcache);
} else {
ret = KVM_PGT_FN(kvm_pgtable_stage2_map)(pgt, fault_ipa, vma_pagesize,
__pfn_to_phys(pfn), prot,
@@ -1885,8 +1985,15 @@ int kvm_handle_guest_abort(struct kvm_vcpu *vcpu)
nested = &nested_trans;
}

- gfn = ipa >> PAGE_SHIFT;
+ gfn = kvm_gpa_from_fault(vcpu->kvm, ipa) >> PAGE_SHIFT;
memslot = gfn_to_memslot(vcpu->kvm, gfn);
+
+ if (kvm_slot_can_be_private(memslot)) {
+ ret = private_memslot_fault(vcpu, ipa, memslot);
+ if (ret != -EINVAL)
+ goto out;
+ }
+
hva = gfn_to_hva_memslot_prot(memslot, gfn, &writable);
write_fault = kvm_is_write_fault(vcpu);
if (kvm_is_error_hva(hva) || (write_fault && !writable)) {
@@ -1930,7 +2037,7 @@ int kvm_handle_guest_abort(struct kvm_vcpu *vcpu)
* of the page size.
*/
ipa |= kvm_vcpu_get_hfar(vcpu) & GENMASK(11, 0);
- ret = io_mem_abort(vcpu, ipa);
+ ret = io_mem_abort(vcpu, kvm_gpa_from_fault(vcpu->kvm, ipa));
goto out_unlock;
}

@@ -1978,6 +2085,10 @@ bool kvm_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range)
if (!kvm->arch.mmu.pgt)
return false;

+ /* We don't support aging for Realms */
+ if (kvm_is_realm(kvm))
+ return true;
+
return KVM_PGT_FN(kvm_pgtable_stage2_test_clear_young)(kvm->arch.mmu.pgt,
range->start << PAGE_SHIFT,
size, true);
@@ -1994,6 +2105,10 @@ bool kvm_test_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range)
if (!kvm->arch.mmu.pgt)
return false;

+ /* We don't support aging for Realms */
+ if (kvm_is_realm(kvm))
+ return true;
+
return KVM_PGT_FN(kvm_pgtable_stage2_test_clear_young)(kvm->arch.mmu.pgt,
range->start << PAGE_SHIFT,
size, false);
diff --git a/arch/arm64/kvm/rme.c b/arch/arm64/kvm/rme.c
index 7880894db722..4b5bb7e49c4f 100644
--- a/arch/arm64/kvm/rme.c
+++ b/arch/arm64/kvm/rme.c
@@ -714,6 +714,182 @@ static int realm_create_protected_data_page(struct realm *realm,
return -ENXIO;
}

+static int fold_rtt(struct realm *realm, unsigned long addr, int level)
+{
+ phys_addr_t rtt_addr;
+ int ret;
+
+ ret = realm_rtt_fold(realm, addr, level, &rtt_addr);
+ if (ret)
+ return ret;
+
+ free_delegated_granule(rtt_addr);
+
+ return 0;
+}
+
+int realm_map_protected(struct realm *realm,
+ unsigned long ipa,
+ kvm_pfn_t pfn,
+ unsigned long map_size,
+ struct kvm_mmu_memory_cache *memcache)
+{
+ phys_addr_t phys = __pfn_to_phys(pfn);
+ phys_addr_t rd = virt_to_phys(realm->rd);
+ unsigned long base_ipa = ipa;
+ unsigned long size;
+ int map_level;
+ int ret = 0;
+
+ if (WARN_ON(!IS_ALIGNED(map_size, RMM_PAGE_SIZE)))
+ return -EINVAL;
+
+ if (WARN_ON(!IS_ALIGNED(ipa, map_size)))
+ return -EINVAL;
+
+ if (IS_ALIGNED(map_size, RMM_L2_BLOCK_SIZE))
+ map_level = 2;
+ else
+ map_level = 3;
+
+ if (map_level < RMM_RTT_MAX_LEVEL) {
+ /*
+ * A temporary RTT is needed during the map, precreate it,
+ * however if there is an error (e.g. missing parent tables)
+ * this will be handled below.
+ */
+ realm_create_rtt_levels(realm, ipa, map_level,
+ RMM_RTT_MAX_LEVEL, memcache);
+ }
+
+ for (size = 0; size < map_size; size += RMM_PAGE_SIZE) {
+ if (rmi_granule_delegate(phys)) {
+ /*
+ * It's likely we raced with another VCPU on the same
+ * fault. Assume the other VCPU has handled the fault
+ * and return to the guest.
+ */
+ return 0;
+ }
+
+ ret = rmi_data_create_unknown(rd, phys, ipa);
+
+ if (RMI_RETURN_STATUS(ret) == RMI_ERROR_RTT) {
+ /* Create missing RTTs and retry */
+ int level = RMI_RETURN_INDEX(ret);
+
+ WARN_ON(level == RMM_RTT_MAX_LEVEL);
+
+ ret = realm_create_rtt_levels(realm, ipa, level,
+ RMM_RTT_MAX_LEVEL,
+ memcache);
+ if (WARN_ON(ret))
+ goto err_undelegate;
+
+ ret = rmi_data_create_unknown(rd, phys, ipa);
+ }
+
+ if (WARN_ON(ret))
+ goto err_undelegate;
+
+ phys += RMM_PAGE_SIZE;
+ ipa += RMM_PAGE_SIZE;
+ }
+
+ if (map_size == RMM_L2_BLOCK_SIZE) {
+ ret = fold_rtt(realm, base_ipa, map_level + 1);
+ if (WARN_ON(ret))
+ goto err;
+ }
+
+ return 0;
+
+err_undelegate:
+ if (WARN_ON(rmi_granule_undelegate(phys))) {
+ /* Page can't be returned to NS world so is lost */
+ get_page(phys_to_page(phys));
+ }
+err:
+ while (size > 0) {
+ unsigned long data, top;
+
+ phys -= RMM_PAGE_SIZE;
+ size -= RMM_PAGE_SIZE;
+ ipa -= RMM_PAGE_SIZE;
+
+ WARN_ON(rmi_data_destroy(rd, ipa, &data, &top));
+
+ if (WARN_ON(rmi_granule_undelegate(phys))) {
+ /* Page can't be returned to NS world so is lost */
+ get_page(phys_to_page(phys));
+ }
+ }
+ return -ENXIO;
+}
+
+int realm_map_non_secure(struct realm *realm,
+ unsigned long ipa,
+ kvm_pfn_t pfn,
+ unsigned long size,
+ struct kvm_mmu_memory_cache *memcache)
+{
+ phys_addr_t rd = virt_to_phys(realm->rd);
+ phys_addr_t phys = __pfn_to_phys(pfn);
+ unsigned long offset;
+ int map_size, map_level;
+ int ret = 0;
+
+ if (WARN_ON(!IS_ALIGNED(size, RMM_PAGE_SIZE)))
+ return -EINVAL;
+
+ if (WARN_ON(!IS_ALIGNED(ipa, size)))
+ return -EINVAL;
+
+ if (IS_ALIGNED(size, RMM_L2_BLOCK_SIZE)) {
+ map_level = 2;
+ map_size = RMM_L2_BLOCK_SIZE;
+ } else {
+ map_level = 3;
+ map_size = RMM_PAGE_SIZE;
+ }
+
+ for (offset = 0; offset < size; offset += map_size) {
+ unsigned long desc = phys |
+ PTE_S2_MEMATTR(MT_S2_FWB_NORMAL) |
+ /* FIXME: Read+Write permissions for now */
+ (3 << 6);
+ ret = rmi_rtt_map_unprotected(rd, ipa, map_level, desc);
+
+ if (RMI_RETURN_STATUS(ret) == RMI_ERROR_RTT) {
+ /* Create missing RTTs and retry */
+ int level = RMI_RETURN_INDEX(ret);
+
+ ret = realm_create_rtt_levels(realm, ipa, level,
+ map_level, memcache);
+ if (WARN_ON(ret))
+ return -ENXIO;
+
+ ret = rmi_rtt_map_unprotected(rd, ipa, map_level, desc);
+ }
+ /*
+ * RMI_ERROR_RTT can be reported for two reasons: either the
+ * RTT tables are not there, or there is an RTTE already
+ * present for the address. The call to
+ * realm_create_rtt_levels() above handles the first case, and
+ * in the second case this indicates that another thread has
+ * already populated the RTTE for us, so we can ignore the
+ * error and continue.
+ */
+ if (ret && RMI_RETURN_STATUS(ret) != RMI_ERROR_RTT)
+ return -ENXIO;
+
+ ipa += map_size;
+ phys += map_size;
+ }
+
+ return 0;
+}
+
static int populate_region(struct kvm *kvm,
phys_addr_t ipa_base,
phys_addr_t ipa_end,
--
2.43.0