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

From: Yuan Yao
Date: Wed Nov 09 2022 - 00:52:52 EST

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In reply to: Chao Peng: "Re: [PATCH v9 5/8] KVM: Register/unregister the guest private memory regions"
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On Tue, Nov 08, 2022 at 05:41:41PM +0800, Chao Peng wrote:
> On Tue, Nov 08, 2022 at 09:35:06AM +0800, Yuan Yao wrote:
> > 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@xxxxxxxxxxxxxxx>
> > > ---
> > > 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.
>
> The mem_attr_array is consumed in the page fault handler(i.e.
> kvm_mem_is_private() in patch 08) so it should also be protected by
> kvm_mmu_invalidate_begin/end(). E.g. if we change the mem_attr_arry here
> after the page fault handler has read the mem_attr_array, the
> mmu_invalidate_retry_gfn() should return 1 to let the page fault handler
> to retry the fault.

You're right!
Even the changes are undo by error handling path, we still need to
sure that user of mem_attr_arry retry the fault, due to the user may
get some "stale" data (they're "stale" becaus the xarray is recovered
in error case).

>
> >
> > > +
> > > + 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.
>
> Ah, right!
>
> Thanks,
> Chao
> >
> > > +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
> > >
> > >

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