Re: [PATCH v9 5/8] KVM: Register/unregister the guest private memory regions

Yuan Yao
2022-11-08T01:35:32Z

On Tue, Oct 25, 2022 at 11:13:41PM +0800, Chao Peng wrote:
> Introduce generic private memory register/unregister by reusing existing
> SEV ioctls KVM_MEMORY_ENCRYPT_{UN,}REG_REGION. It differs from SEV case
> by treating address in the region as gpa instead of hva. Which cases
> should these ioctls go is determined by the kvm_arch_has_private_mem().
> Architecture which supports KVM_PRIVATE_MEM should override this function.
>
> KVM internally defaults all guest memory as private memory and maintain
> the shared memory in 'mem_attr_array'. The above ioctls operate on this
> field and unmap existing mappings if any.
>
> Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
> ---
> Documentation/virt/kvm/api.rst | 17 ++-
> arch/x86/kvm/Kconfig | 1 +
> include/linux/kvm_host.h | 10 +-
> virt/kvm/Kconfig | 4 +
> virt/kvm/kvm_main.c | 227 +++++++++++++++++++++++++--------
> 5 files changed, 198 insertions(+), 61 deletions(-)
>
> diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
> index 975688912b8c..08253cf498d1 100644
> --- a/Documentation/virt/kvm/api.rst
> +++ b/Documentation/virt/kvm/api.rst
> @@ -4717,10 +4717,19 @@ Documentation/virt/kvm/x86/amd-memory-encryption.rst.
> This ioctl can be used to register a guest memory region which may
> contain encrypted data (e.g. guest RAM, SMRAM etc).
>
> -It is used in the SEV-enabled guest. When encryption is enabled, a guest
> -memory region may contain encrypted data. The SEV memory encryption
> -engine uses a tweak such that two identical plaintext pages, each at
> -different locations will have differing ciphertexts. So swapping or
> +Currently this ioctl supports registering memory regions for two usages:
> +private memory and SEV-encrypted memory.
> +
> +When private memory is enabled, this ioctl is used to register guest private
> +memory region and the addr/size of kvm_enc_region represents guest physical
> +address (GPA). In this usage, this ioctl zaps the existing guest memory
> +mappings in KVM that fallen into the region.
> +
> +When SEV-encrypted memory is enabled, this ioctl is used to register guest
> +memory region which may contain encrypted data for a SEV-enabled guest. The
> +addr/size of kvm_enc_region represents userspace address (HVA). The SEV
> +memory encryption engine uses a tweak such that two identical plaintext pages,
> +each at different locations will have differing ciphertexts. So swapping or
> moving ciphertext of those pages will not result in plaintext being
> swapped. So relocating (or migrating) physical backing pages for the SEV
> guest will require some additional steps.
> diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
> index 8d2bd455c0cd..73fdfa429b20 100644
> --- a/arch/x86/kvm/Kconfig
> +++ b/arch/x86/kvm/Kconfig
> @@ -51,6 +51,7 @@ config KVM
> select HAVE_KVM_PM_NOTIFIER if PM
> select HAVE_KVM_RESTRICTED_MEM if X86_64
> select RESTRICTEDMEM if HAVE_KVM_RESTRICTED_MEM
> + select KVM_GENERIC_PRIVATE_MEM if HAVE_KVM_RESTRICTED_MEM
> help
> Support hosting fully virtualized guest machines using hardware
> virtualization extensions. You will need a fairly recent
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 79e5cbc35fcf..4ce98fa0153c 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -245,7 +245,8 @@ bool kvm_setup_async_pf(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
> int kvm_async_pf_wakeup_all(struct kvm_vcpu *vcpu);
> #endif
>
> -#ifdef KVM_ARCH_WANT_MMU_NOTIFIER
> +
> +#if defined(KVM_ARCH_WANT_MMU_NOTIFIER) || defined(CONFIG_KVM_GENERIC_PRIVATE_MEM)
> struct kvm_gfn_range {
> struct kvm_memory_slot *slot;
> gfn_t start;
> @@ -254,6 +255,9 @@ struct kvm_gfn_range {
> bool may_block;
> };
> bool kvm_unmap_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range);
> +#endif
> +
> +#ifdef KVM_ARCH_WANT_MMU_NOTIFIER
> bool kvm_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range);
> bool kvm_test_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range);
> bool kvm_set_spte_gfn(struct kvm *kvm, struct kvm_gfn_range *range);
> @@ -794,6 +798,9 @@ struct kvm {
> struct notifier_block pm_notifier;
> #endif
> char stats_id[KVM_STATS_NAME_SIZE];
> +#ifdef CONFIG_KVM_GENERIC_PRIVATE_MEM
> + struct xarray mem_attr_array;
> +#endif
> };
>
> #define kvm_err(fmt, ...) \
> @@ -1453,6 +1460,7 @@ bool kvm_arch_dy_has_pending_interrupt(struct kvm_vcpu *vcpu);
> int kvm_arch_post_init_vm(struct kvm *kvm);
> void kvm_arch_pre_destroy_vm(struct kvm *kvm);
> int kvm_arch_create_vm_debugfs(struct kvm *kvm);
> +bool kvm_arch_has_private_mem(struct kvm *kvm);
>
> #ifndef __KVM_HAVE_ARCH_VM_ALLOC
> /*
> diff --git a/virt/kvm/Kconfig b/virt/kvm/Kconfig
> index 9ff164c7e0cc..69ca59e82149 100644
> --- a/virt/kvm/Kconfig
> +++ b/virt/kvm/Kconfig
> @@ -89,3 +89,7 @@ config HAVE_KVM_PM_NOTIFIER
>
> config HAVE_KVM_RESTRICTED_MEM
> bool
> +
> +config KVM_GENERIC_PRIVATE_MEM
> + bool
> + depends on HAVE_KVM_RESTRICTED_MEM
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 09c9cdeb773c..fc3835826ace 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -520,6 +520,62 @@ void kvm_destroy_vcpus(struct kvm *kvm)
> }
> EXPORT_SYMBOL_GPL(kvm_destroy_vcpus);
>
> +static inline void update_invalidate_range(struct kvm *kvm, gfn_t start,
> + gfn_t end)
> +{
> + if (likely(kvm->mmu_invalidate_in_progress == 1)) {
> + kvm->mmu_invalidate_range_start = start;
> + kvm->mmu_invalidate_range_end = end;
> + } else {
> + /*
> + * Fully tracking multiple concurrent ranges has diminishing
> + * returns. Keep things simple and just find the minimal range
> + * which includes the current and new ranges. As there won't be
> + * enough information to subtract a range after its invalidate
> + * completes, any ranges invalidated concurrently will
> + * accumulate and persist until all outstanding invalidates
> + * complete.
> + */
> + kvm->mmu_invalidate_range_start =
> + min(kvm->mmu_invalidate_range_start, start);
> + kvm->mmu_invalidate_range_end =
> + max(kvm->mmu_invalidate_range_end, end);
> + }
> +}
> +
> +static void mark_invalidate_in_progress(struct kvm *kvm, gfn_t start, gfn_t end)
> +{
> + /*
> + * The count increase must become visible at unlock time as no
> + * spte can be established without taking the mmu_lock and
> + * count is also read inside the mmu_lock critical section.
> + */
> + kvm->mmu_invalidate_in_progress++;
> +}
> +
> +void kvm_mmu_invalidate_begin(struct kvm *kvm, gfn_t start, gfn_t end)
> +{
> + mark_invalidate_in_progress(kvm, start, end);
> + update_invalidate_range(kvm, start, end);
> +}
> +
> +void kvm_mmu_invalidate_end(struct kvm *kvm, gfn_t start, gfn_t end)
> +{
> + /*
> + * This sequence increase will notify the kvm page fault that
> + * the page that is going to be mapped in the spte could have
> + * been freed.
> + */
> + kvm->mmu_invalidate_seq++;
> + smp_wmb();
> + /*
> + * The above sequence increase must be visible before the
> + * below count decrease, which is ensured by the smp_wmb above
> + * in conjunction with the smp_rmb in mmu_invalidate_retry().
> + */
> + kvm->mmu_invalidate_in_progress--;
> +}
> +
> #if defined(CONFIG_MMU_NOTIFIER) && defined(KVM_ARCH_WANT_MMU_NOTIFIER)
> static inline struct kvm *mmu_notifier_to_kvm(struct mmu_notifier *mn)
> {
> @@ -715,51 +771,12 @@ static void kvm_mmu_notifier_change_pte(struct mmu_notifier *mn,
> kvm_handle_hva_range(mn, address, address + 1, pte, kvm_set_spte_gfn);
> }
>
> -static inline void update_invalidate_range(struct kvm *kvm, gfn_t start,
> - gfn_t end)
> -{
> - if (likely(kvm->mmu_invalidate_in_progress == 1)) {
> - kvm->mmu_invalidate_range_start = start;
> - kvm->mmu_invalidate_range_end = end;
> - } else {
> - /*
> - * Fully tracking multiple concurrent ranges has diminishing
> - * returns. Keep things simple and just find the minimal range
> - * which includes the current and new ranges. As there won't be
> - * enough information to subtract a range after its invalidate
> - * completes, any ranges invalidated concurrently will
> - * accumulate and persist until all outstanding invalidates
> - * complete.
> - */
> - kvm->mmu_invalidate_range_start =
> - min(kvm->mmu_invalidate_range_start, start);
> - kvm->mmu_invalidate_range_end =
> - max(kvm->mmu_invalidate_range_end, end);
> - }
> -}
> -
> -static void mark_invalidate_in_progress(struct kvm *kvm, gfn_t start, gfn_t end)
> -{
> - /*
> - * The count increase must become visible at unlock time as no
> - * spte can be established without taking the mmu_lock and
> - * count is also read inside the mmu_lock critical section.
> - */
> - kvm->mmu_invalidate_in_progress++;
> -}
> -
> static bool kvm_mmu_handle_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range)
> {
> update_invalidate_range(kvm, range->start, range->end);
> return kvm_unmap_gfn_range(kvm, range);
> }
>
> -void kvm_mmu_invalidate_begin(struct kvm *kvm, gfn_t start, gfn_t end)
> -{
> - mark_invalidate_in_progress(kvm, start, end);
> - update_invalidate_range(kvm, start, end);
> -}
> -
> static int kvm_mmu_notifier_invalidate_range_start(struct mmu_notifier *mn,
> const struct mmu_notifier_range *range)
> {
> @@ -807,23 +824,6 @@ static int kvm_mmu_notifier_invalidate_range_start(struct mmu_notifier *mn,
> return 0;
> }
>
> -void kvm_mmu_invalidate_end(struct kvm *kvm, gfn_t start, gfn_t end)
> -{
> - /*
> - * This sequence increase will notify the kvm page fault that
> - * the page that is going to be mapped in the spte could have
> - * been freed.
> - */
> - kvm->mmu_invalidate_seq++;
> - smp_wmb();
> - /*
> - * The above sequence increase must be visible before the
> - * below count decrease, which is ensured by the smp_wmb above
> - * in conjunction with the smp_rmb in mmu_invalidate_retry().
> - */
> - kvm->mmu_invalidate_in_progress--;
> -}
> -
> static void kvm_mmu_notifier_invalidate_range_end(struct mmu_notifier *mn,
> const struct mmu_notifier_range *range)
> {
> @@ -937,6 +937,89 @@ static int kvm_init_mmu_notifier(struct kvm *kvm)
>
> #endif /* CONFIG_MMU_NOTIFIER && KVM_ARCH_WANT_MMU_NOTIFIER */
>
> +#ifdef CONFIG_KVM_GENERIC_PRIVATE_MEM
> +
> +static void kvm_unmap_mem_range(struct kvm *kvm, gfn_t start, gfn_t end)
> +{
> + struct kvm_gfn_range gfn_range;
> + struct kvm_memory_slot *slot;
> + struct kvm_memslots *slots;
> + struct kvm_memslot_iter iter;
> + int i;
> + int r = 0;
> +
> + gfn_range.pte = __pte(0);
> + gfn_range.may_block = true;
> +
> + for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) {
> + slots = __kvm_memslots(kvm, i);
> +
> + kvm_for_each_memslot_in_gfn_range(&iter, slots, start, end) {
> + slot = iter.slot;
> + gfn_range.start = max(start, slot->base_gfn);
> + gfn_range.end = min(end, slot->base_gfn + slot->npages);
> + if (gfn_range.start >= gfn_range.end)
> + continue;
> + gfn_range.slot = slot;
> +
> + r |= kvm_unmap_gfn_range(kvm, &gfn_range);
> + }
> + }
> +
> + if (r)
> + kvm_flush_remote_tlbs(kvm);
> +}
> +
> +#define KVM_MEM_ATTR_SHARED 0x0001
> +static int kvm_vm_ioctl_set_mem_attr(struct kvm *kvm, gpa_t gpa, gpa_t size,
> + bool is_private)
> +{
> + gfn_t start, end;
> + unsigned long i;
> + void *entry;
> + int idx;
> + int r = 0;
> +
> + if (size == 0 || gpa + size < gpa)
> + return -EINVAL;
> + if (gpa & (PAGE_SIZE - 1) || size & (PAGE_SIZE - 1))
> + return -EINVAL;
> +
> + start = gpa >> PAGE_SHIFT;
> + end = (gpa + size - 1 + PAGE_SIZE) >> PAGE_SHIFT;
> +
> + /*
> + * Guest memory defaults to private, kvm->mem_attr_array only stores
> + * shared memory.
> + */
> + entry = is_private ? NULL : xa_mk_value(KVM_MEM_ATTR_SHARED);
> +
> + idx = srcu_read_lock(&kvm->srcu);
> + KVM_MMU_LOCK(kvm);
> + kvm_mmu_invalidate_begin(kvm, start, end);
> +
> + for (i = start; i < end; i++) {
> + r = xa_err(xa_store(&kvm->mem_attr_array, i, entry,
> + GFP_KERNEL_ACCOUNT));
> + if (r)
> + goto err;
> + }
> +
> + kvm_unmap_mem_range(kvm, start, end);

lock is hold by KVM_MMU_LOCK() so how about do
kvm_mmu_invalidate_begin() after changing xarray:

kvm_mmu_invalidate_begin(kvm, start, end);
kvm_unmap_mem_range(kvm, start, end);
kvm_mmu_invalidate_end(kvm, start, end);

Also the error handling path doesn't need to care it yet.

> +
> + goto ret;
> +err:
> + for (; i > start; i--)
> + xa_erase(&kvm->mem_attr_array, i);

the start should be covered yet, consider the i is
unsigned long and case of start is 0, may need another
variable j for this.

> +ret:
> + kvm_mmu_invalidate_end(kvm, start, end);
> + KVM_MMU_UNLOCK(kvm);
> + srcu_read_unlock(&kvm->srcu, idx);
> +
> + return r;
> +}
> +#endif /* CONFIG_KVM_GENERIC_PRIVATE_MEM */
> +
> #ifdef CONFIG_HAVE_KVM_PM_NOTIFIER
> static int kvm_pm_notifier_call(struct notifier_block *bl,
> unsigned long state,
> @@ -1165,6 +1248,9 @@ static struct kvm *kvm_create_vm(unsigned long type, const char *fdname)
> spin_lock_init(&kvm->mn_invalidate_lock);
> rcuwait_init(&kvm->mn_memslots_update_rcuwait);
> xa_init(&kvm->vcpu_array);
> +#ifdef CONFIG_KVM_GENERIC_PRIVATE_MEM
> + xa_init(&kvm->mem_attr_array);
> +#endif
>
> INIT_LIST_HEAD(&kvm->gpc_list);
> spin_lock_init(&kvm->gpc_lock);
> @@ -1338,6 +1424,9 @@ static void kvm_destroy_vm(struct kvm *kvm)
> kvm_free_memslots(kvm, &kvm->__memslots[i][0]);
> kvm_free_memslots(kvm, &kvm->__memslots[i][1]);
> }
> +#ifdef CONFIG_KVM_GENERIC_PRIVATE_MEM
> + xa_destroy(&kvm->mem_attr_array);
> +#endif
> cleanup_srcu_struct(&kvm->irq_srcu);
> cleanup_srcu_struct(&kvm->srcu);
> kvm_arch_free_vm(kvm);
> @@ -1541,6 +1630,11 @@ static void kvm_replace_memslot(struct kvm *kvm,
> }
> }
>
> +bool __weak kvm_arch_has_private_mem(struct kvm *kvm)
> +{
> + return false;
> +}
> +
> static int check_memory_region_flags(const struct kvm_user_mem_region *mem)
> {
> u32 valid_flags = KVM_MEM_LOG_DIRTY_PAGES;
> @@ -4708,6 +4802,24 @@ static long kvm_vm_ioctl(struct file *filp,
> r = kvm_vm_ioctl_set_memory_region(kvm, &mem);
> break;
> }
> +#ifdef CONFIG_KVM_GENERIC_PRIVATE_MEM
> + case KVM_MEMORY_ENCRYPT_REG_REGION:
> + case KVM_MEMORY_ENCRYPT_UNREG_REGION: {
> + struct kvm_enc_region region;
> + bool set = ioctl == KVM_MEMORY_ENCRYPT_REG_REGION;
> +
> + if (!kvm_arch_has_private_mem(kvm))
> + goto arch_vm_ioctl;
> +
> + r = -EFAULT;
> + if (copy_from_user(&region, argp, sizeof(region)))
> + goto out;
> +
> + r = kvm_vm_ioctl_set_mem_attr(kvm, region.addr,
> + region.size, set);
> + break;
> + }
> +#endif
> case KVM_GET_DIRTY_LOG: {
> struct kvm_dirty_log log;
>
> @@ -4861,6 +4973,9 @@ static long kvm_vm_ioctl(struct file *filp,
> r = kvm_vm_ioctl_get_stats_fd(kvm);
> break;
> default:
> +#ifdef CONFIG_KVM_GENERIC_PRIVATE_MEM
> +arch_vm_ioctl:
> +#endif
> r = kvm_arch_vm_ioctl(filp, ioctl, arg);
> }
> out:
> --
> 2.25.1
>
>