Re: [PATCH v2 21/43] arm64: RME: Runtime faulting of memory

Fuad Tabba
2024-04-25T10:43:40Z

Hi,

On Fri, Apr 12, 2024 at 9:44 AM Steven Price <steven.price@arm.com> wrote:
>
> 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>
> ---
> arch/arm64/include/asm/kvm_emulate.h | 10 ++
> arch/arm64/include/asm/kvm_rme.h | 10 ++
> arch/arm64/kvm/mmu.c | 119 +++++++++++++++-
> arch/arm64/kvm/rme.c | 199 ++++++++++++++++++++++++---
> 4 files changed, 316 insertions(+), 22 deletions(-)
>
> diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h
> index 2209a7c6267f..d40d998d9be2 100644
> --- a/arch/arm64/include/asm/kvm_emulate.h
> +++ b/arch/arm64/include/asm/kvm_emulate.h
> @@ -629,6 +629,16 @@ 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_stolen_bits(struct kvm *kvm)
> +{
> + if (kvm_is_realm(kvm)) {
> + struct realm *realm = &kvm->arch.realm;
> +
> + return BIT(realm->ia_bits - 1);
> + }
> + return 0;
> +}
> +
> 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 749f2eb97bd4..48c7766fadeb 100644
> --- a/arch/arm64/include/asm/kvm_rme.h
> +++ b/arch/arm64/include/asm/kvm_rme.h
> @@ -103,6 +103,16 @@ 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,
> + struct page *dst_page,
> + unsigned long map_size,
> + struct kvm_mmu_memory_cache *memcache);
> +int realm_map_non_secure(struct realm *realm,
> + unsigned long ipa,
> + struct page *page,
> + unsigned long map_size,
> + struct kvm_mmu_memory_cache *memcache);
> int realm_set_ipa_state(struct kvm_vcpu *vcpu,
> unsigned long addr, unsigned long end,
> unsigned long ripas);
> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> index 8a7b5449697f..50a49e4e2020 100644
> --- a/arch/arm64/kvm/mmu.c
> +++ b/arch/arm64/kvm/mmu.c
> @@ -325,8 +325,13 @@ 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_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_pgtable_stage2_unmap,
> + may_block));
> }
>
> static void unmap_stage2_range(struct kvm_s2_mmu *mmu, phys_addr_t start, u64 size)
> @@ -340,7 +345,11 @@ 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;
>
> - stage2_apply_range_resched(&kvm->arch.mmu, addr, end, kvm_pgtable_stage2_flush);
> + if (kvm_is_realm(kvm))
> + kvm_realm_unmap_range(kvm, addr, end - addr, false);
> + else
> + stage2_apply_range_resched(&kvm->arch.mmu, addr, end,
> + kvm_pgtable_stage2_flush);
> }
>
> /**
> @@ -997,6 +1006,10 @@ 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);
> @@ -1020,6 +1033,7 @@ 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)) {
> + unmap_stage2_range(mmu, 0, (~0ULL) & PAGE_MASK);
> write_unlock(&kvm->mmu_lock);
> kvm_realm_destroy_rtts(kvm, pgt->ia_bits);
> return;
> @@ -1383,6 +1397,69 @@ 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;
> + struct page *page = pfn_to_page(pfn);
> +
> + if (WARN_ON(!(prot & KVM_PGTABLE_PROT_W)))
> + return -EFAULT;
> +
> + if (!realm_is_addr_protected(realm, ipa))
> + return realm_map_non_secure(realm, ipa, page, map_size,
> + memcache);
> +
> + return realm_map_protected(realm, ipa, page, 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_stolen_mask = kvm_gpa_stolen_bits(kvm);
> + gfn_t gfn = (fault_ipa & ~gpa_stolen_mask) >> PAGE_SHIFT;
> + bool is_priv_gfn = !((fault_ipa & gpa_stolen_mask) == gpa_stolen_mask);
> + bool priv_exists = kvm_mem_is_private(kvm, gfn);
> + struct kvm_mmu_memory_cache *memcache = &vcpu->arch.mmu_page_cache;
> + int order;
> + kvm_pfn_t pfn;
> + int ret;
> +
> + if (priv_exists != is_priv_gfn) {
> + kvm_prepare_memory_fault_exit(vcpu,
> + fault_ipa & ~gpa_stolen_mask,
> + PAGE_SIZE,
> + kvm_is_write_fault(vcpu),
> + false, is_priv_gfn);
> +
> + return 0;
> + }
> +
> + if (!is_priv_gfn) {
> + /* Not a private mapping, handling normally */
> + return -EAGAIN;
> + }
> +
> + if (kvm_gmem_get_pfn(kvm, memslot, gfn, &pfn, &order))
> + return 1; /* Retry */

You don't need to pass a variable to hold the order if you don't need
it. You can pass NULL.

I am also confused about the return, why do you return 1 regardless of
the reason kvm_gmem_get_pfn() fails?

> + ret = kvm_mmu_topup_memory_cache(memcache,
> + kvm_mmu_cache_min_pages(vcpu->arch.hw_mmu));
> + if (ret)
> + return ret;

If this fails you should release the page you got earlier (e.g.,
kvm_release_pfn_clean()), or you could move it before
kvm_gmem_get_pfn().

> + /* 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 */

Should also release the page if it fails. Speaking of which,
where/when do you eventually release the page?

Cheers,
/fuad

> + return ret;
> +}
> +
> static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
> struct kvm_memory_slot *memslot, unsigned long hva,
> bool fault_is_perm)
> @@ -1402,10 +1479,19 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
> long vma_pagesize, fault_granule;
> enum kvm_pgtable_prot prot = KVM_PGTABLE_PROT_R;
> struct kvm_pgtable *pgt;
> + gpa_t gpa_stolen_mask = kvm_gpa_stolen_bits(vcpu->kvm);
>
> 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);
>
> @@ -1478,7 +1564,7 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
> if (vma_pagesize == PMD_SIZE || vma_pagesize == PUD_SIZE)
> fault_ipa &= ~(vma_pagesize - 1);
>
> - gfn = fault_ipa >> PAGE_SHIFT;
> + gfn = (fault_ipa & ~gpa_stolen_mask) >> PAGE_SHIFT;
> mte_allowed = kvm_vma_mte_allowed(vma);
>
> vfio_allow_any_uc = vma->vm_flags & VM_ALLOW_ANY_UNCACHED;
> @@ -1538,7 +1624,8 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
> * If we are not forced to use page mapping, check if we are
> * backed by a THP and thus use block mapping if possible.
> */
> - if (vma_pagesize == PAGE_SIZE && !(force_pte || device)) {
> + /* FIXME: We shouldn't need to disable this for realms */
> + if (vma_pagesize == PAGE_SIZE && !(force_pte || device || kvm_is_realm(kvm))) {
> if (fault_is_perm && fault_granule > PAGE_SIZE)
> vma_pagesize = fault_granule;
> else
> @@ -1584,6 +1671,9 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
> */
> if (fault_is_perm && vma_pagesize == fault_granule)
> ret = kvm_pgtable_stage2_relax_perms(pgt, fault_ipa, prot);
> + else if (kvm_is_realm(kvm))
> + ret = realm_map_ipa(kvm, fault_ipa, pfn, vma_pagesize,
> + prot, memcache);
> else
> ret = kvm_pgtable_stage2_map(pgt, fault_ipa, vma_pagesize,
> __pfn_to_phys(pfn), prot,
> @@ -1638,6 +1728,7 @@ int kvm_handle_guest_abort(struct kvm_vcpu *vcpu)
> struct kvm_memory_slot *memslot;
> unsigned long hva;
> bool is_iabt, write_fault, writable;
> + gpa_t gpa_stolen_mask = kvm_gpa_stolen_bits(vcpu->kvm);
> gfn_t gfn;
> int ret, idx;
>
> @@ -1693,8 +1784,15 @@ int kvm_handle_guest_abort(struct kvm_vcpu *vcpu)
>
> idx = srcu_read_lock(&vcpu->kvm->srcu);
>
> - gfn = fault_ipa >> PAGE_SHIFT;
> + gfn = (fault_ipa & ~gpa_stolen_mask) >> PAGE_SHIFT;
> memslot = gfn_to_memslot(vcpu->kvm, gfn);
> +
> + if (kvm_slot_can_be_private(memslot)) {
> + ret = private_memslot_fault(vcpu, fault_ipa, memslot);
> + if (ret != -EAGAIN)
> + 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)) {
> @@ -1738,6 +1836,7 @@ int kvm_handle_guest_abort(struct kvm_vcpu *vcpu)
> * of the page size.
> */
> fault_ipa |= kvm_vcpu_get_hfar(vcpu) & ((1 << 12) - 1);
> + fault_ipa &= ~gpa_stolen_mask;
> ret = io_mem_abort(vcpu, fault_ipa);
> goto out_unlock;
> }
> @@ -1819,6 +1918,10 @@ 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_pgtable_stage2_test_clear_young(kvm->arch.mmu.pgt,
> range->start << PAGE_SHIFT,
> size, true);
> @@ -1831,6 +1934,10 @@ 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_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 4aab507f896e..72f6f5f542c4 100644
> --- a/arch/arm64/kvm/rme.c
> +++ b/arch/arm64/kvm/rme.c
> @@ -606,6 +606,170 @@ static int fold_rtt(struct realm *realm, unsigned long addr, int level)
> return 0;
> }
>
> +int realm_map_protected(struct realm *realm,
> + unsigned long base_ipa,
> + struct page *dst_page,
> + unsigned long map_size,
> + struct kvm_mmu_memory_cache *memcache)
> +{
> + phys_addr_t dst_phys = page_to_phys(dst_page);
> + phys_addr_t rd = virt_to_phys(realm->rd);
> + unsigned long phys = dst_phys;
> + unsigned long ipa = base_ipa;
> + unsigned long size;
> + int map_level;
> + int ret = 0;
> +
> + if (WARN_ON(!IS_ALIGNED(ipa, map_size)))
> + return -EINVAL;
> +
> + switch (map_size) {
> + case PAGE_SIZE:
> + map_level = 3;
> + break;
> + case RME_L2_BLOCK_SIZE:
> + map_level = 2;
> + break;
> + default:
> + return -EINVAL;
> + }
> +
> + if (map_level < RME_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,
> + RME_RTT_MAX_LEVEL, memcache);
> + }
> +
> + for (size = 0; size < map_size; size += PAGE_SIZE) {
> + if (rmi_granule_delegate(phys)) {
> + struct rtt_entry rtt;
> +
> + /*
> + * It's possible we raced with another VCPU on the same
> + * fault. If the entry exists and matches then exit
> + * early and assume the other VCPU will handle the
> + * mapping.
> + */
> + if (rmi_rtt_read_entry(rd, ipa, RME_RTT_MAX_LEVEL, &rtt))
> + goto err;
> +
> + // FIXME: For a block mapping this could race at level
> + // 2 or 3...
> + if (WARN_ON((rtt.walk_level != RME_RTT_MAX_LEVEL ||
> + rtt.state != RMI_ASSIGNED ||
> + rtt.desc != phys))) {
> + goto err;
> + }
> +
> + 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);
> +
> + ret = realm_create_rtt_levels(realm, ipa, level,
> + RME_RTT_MAX_LEVEL,
> + memcache);
> + WARN_ON(ret);
> + if (ret)
> + goto err_undelegate;
> +
> + ret = rmi_data_create_unknown(rd, phys, ipa);
> + }
> + WARN_ON(ret);
> +
> + if (ret)
> + goto err_undelegate;
> +
> + phys += PAGE_SIZE;
> + ipa += PAGE_SIZE;
> + }
> +
> + if (map_size == RME_L2_BLOCK_SIZE)
> + ret = fold_rtt(realm, base_ipa, map_level);
> + 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 -= PAGE_SIZE;
> + size -= PAGE_SIZE;
> + ipa -= 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,
> + struct page *page,
> + unsigned long map_size,
> + struct kvm_mmu_memory_cache *memcache)
> +{
> + phys_addr_t rd = virt_to_phys(realm->rd);
> + int map_level;
> + int ret = 0;
> + unsigned long desc = page_to_phys(page) |
> + PTE_S2_MEMATTR(MT_S2_FWB_NORMAL) |
> + /* FIXME: Read+Write permissions for now */
> + (3 << 6) |
> + PTE_SHARED;
> +
> + if (WARN_ON(!IS_ALIGNED(ipa, map_size)))
> + return -EINVAL;
> +
> + switch (map_size) {
> + case PAGE_SIZE:
> + map_level = 3;
> + break;
> + case RME_L2_BLOCK_SIZE:
> + map_level = 2;
> + break;
> + default:
> + return -EINVAL;
> + }
> +
> + 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);
> + }
> + if (WARN_ON(ret))
> + return -ENXIO;
> +
> + return 0;
> +}
> +
> static int populate_par_region(struct kvm *kvm,
> phys_addr_t ipa_base,
> phys_addr_t ipa_end,
> @@ -617,7 +781,6 @@ static int populate_par_region(struct kvm *kvm,
> int idx;
> phys_addr_t ipa;
> int ret = 0;
> - struct page *tmp_page;
> unsigned long data_flags = 0;
>
> base_gfn = gpa_to_gfn(ipa_base);
> @@ -639,9 +802,8 @@ static int populate_par_region(struct kvm *kvm,
> goto out;
> }
>
> - tmp_page = alloc_page(GFP_KERNEL);
> - if (!tmp_page) {
> - ret = -ENOMEM;
> + if (!kvm_slot_can_be_private(memslot)) {
> + ret = -EINVAL;
> goto out;
> }
>
> @@ -714,31 +876,36 @@ static int populate_par_region(struct kvm *kvm,
> for (offset = 0; offset < map_size && !ret;
> offset += PAGE_SIZE, page++) {
> phys_addr_t page_ipa = ipa + offset;
> + kvm_pfn_t priv_pfn;
> + int order;
>
> - ret = realm_create_protected_data_page(realm, page_ipa,
> - page, tmp_page,
> - data_flags);
> + ret = kvm_gmem_get_pfn(kvm, memslot,
> + page_ipa >> PAGE_SHIFT,
> + &priv_pfn, &order);
> + if (ret)
> + break;
> +
> + ret = realm_create_protected_data_page(
> + realm, page_ipa,
> + pfn_to_page(priv_pfn),
> + page, data_flags);
> }
> +
> + kvm_release_pfn_clean(pfn);
> +
> if (ret)
> - goto err_release_pfn;
> + break;
>
> if (level == 2) {
> ret = fold_rtt(realm, ipa, level);
> if (ret)
> - goto err_release_pfn;
> + break;
> }
>
> ipa += map_size;
> - kvm_release_pfn_dirty(pfn);
> -err_release_pfn:
> - if (ret) {
> - kvm_release_pfn_clean(pfn);
> - break;
> - }
> }
>
> mmap_read_unlock(current->mm);
> - __free_page(tmp_page);
>
> out:
> srcu_read_unlock(&kvm->srcu, idx);
> --
> 2.34.1
>