Re: [PATCH v10 6/9] KVM: Unmap existing mappings when change the memory attributes

[Yuan Yao]

On Thu, Dec 08, 2022 at 07:20:43PM +0800, Chao Peng wrote:
> On Wed, Dec 07, 2022 at 04:13:14PM +0800, Yuan Yao wrote:
> > On Fri, Dec 02, 2022 at 02:13:44PM +0800, Chao Peng wrote:
> > > Unmap the existing guest mappings when memory attribute is changed
> > > between shared and private. This is needed because shared pages and
> > > private pages are from different backends, unmapping existing ones
> > > gives a chance for page fault handler to re-populate the mappings
> > > according to the new attribute.
> > >
> > > Only architecture has private memory support needs this and the
> > > supported architecture is expected to rewrite the weak
> > > kvm_arch_has_private_mem().
> > >
> > > Also, during memory attribute changing and the unmapping time frame,
> > > page fault handler may happen in the same memory range and can cause
> > > incorrect page state, invoke kvm_mmu_invalidate_* helpers to let the
> > > page fault handler retry during this time frame.
> > >
> > > Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
> > > ---
> > >  include/linux/kvm_host.h |   7 +-
> > >  virt/kvm/kvm_main.c      | 168 ++++++++++++++++++++++++++-------------
> > >  2 files changed, 116 insertions(+), 59 deletions(-)
> > >
> > > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> > > index 3d69484d2704..3331c0c92838 100644
> > > --- a/include/linux/kvm_host.h
> > > +++ b/include/linux/kvm_host.h
> > > @@ -255,7 +255,6 @@ 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
> > >  struct kvm_gfn_range {
> > >   struct kvm_memory_slot *slot;
> > >   gfn_t start;
> > > @@ -264,6 +263,8 @@ struct kvm_gfn_range {
> > >   bool may_block;
> > >  };
> > >  bool kvm_unmap_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range);
> > > +
> > > +#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);
> > > @@ -785,11 +786,12 @@ struct kvm {
> > >
> > >  #if defined(CONFIG_MMU_NOTIFIER) && defined(KVM_ARCH_WANT_MMU_NOTIFIER)
> > >   struct mmu_notifier mmu_notifier;
> > > +#endif
> > >   unsigned long mmu_invalidate_seq;
> > >   long mmu_invalidate_in_progress;
> > >   gfn_t mmu_invalidate_range_start;
> > >   gfn_t mmu_invalidate_range_end;
> > > -#endif
> > > +
> > >   struct list_head devices;
> > >   u64 manual_dirty_log_protect;
> > >   struct dentry *debugfs_dentry;
> > > @@ -1480,6 +1482,7 @@ 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/kvm_main.c b/virt/kvm/kvm_main.c
> > > index ad55dfbc75d7..4e1e1e113bf0 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);
> > >
> > > +void kvm_mmu_invalidate_begin(struct kvm *kvm)
> > > +{
> > > + /*
> > > +  * 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++;
> > > +
> > > + if (likely(kvm->mmu_invalidate_in_progress == 1)) {
> > > +         kvm->mmu_invalidate_range_start = INVALID_GPA;
> > > +         kvm->mmu_invalidate_range_end = INVALID_GPA;
> > > + }
> > > +}
> > > +
> > > +void kvm_mmu_invalidate_range_add(struct kvm *kvm, gfn_t start, gfn_t 
> > > end)
> > > +{
> > > + WARN_ON_ONCE(!kvm->mmu_invalidate_in_progress);
> > > +
> > > + 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);
> > > + }
> > > +}
> > > +
> > > +void kvm_mmu_invalidate_end(struct kvm *kvm)
> > > +{
> > > + /*
> > > +  * 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)
> > >  {
> > > @@ -714,45 +770,6 @@ static void kvm_mmu_notifier_change_pte(struct 
> > > mmu_notifier *mn,
> > >   kvm_handle_hva_range(mn, address, address + 1, pte, kvm_set_spte_gfn);
> > >  }
> > >
> > > -void kvm_mmu_invalidate_begin(struct kvm *kvm)
> > > -{
> > > - /*
> > > -  * 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++;
> > > -
> > > - if (likely(kvm->mmu_invalidate_in_progress == 1)) {
> > > -         kvm->mmu_invalidate_range_start = INVALID_GPA;
> > > -         kvm->mmu_invalidate_range_end = INVALID_GPA;
> > > - }
> > > -}
> > > -
> > > -void kvm_mmu_invalidate_range_add(struct kvm *kvm, gfn_t start, gfn_t 
> > > end)
> > > -{
> > > - WARN_ON_ONCE(!kvm->mmu_invalidate_in_progress);
> > > -
> > > - 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 bool kvm_mmu_unmap_gfn_range(struct kvm *kvm, struct 
> > > kvm_gfn_range *range)
> > >  {
> > >   kvm_mmu_invalidate_range_add(kvm, range->start, range->end);
> > > @@ -806,23 +823,6 @@ static int 
> > > kvm_mmu_notifier_invalidate_range_start(struct mmu_notifier *mn,
> > >   return 0;
> > >  }
> > >
> > > -void kvm_mmu_invalidate_end(struct kvm *kvm)
> > > -{
> > > - /*
> > > -  * 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)
> > >  {
> > > @@ -1140,6 +1140,11 @@ int __weak kvm_arch_create_vm_debugfs(struct kvm 
> > > *kvm)
> > >   return 0;
> > >  }
> > >
> > > +bool __weak kvm_arch_has_private_mem(struct kvm *kvm)
> > > +{
> > > + return false;
> > > +}
> > > +
> > >  static struct kvm *kvm_create_vm(unsigned long type, const char *fdname)
> > >  {
> > >   struct kvm *kvm = kvm_arch_alloc_vm();
> > > @@ -2349,15 +2354,47 @@ static u64 kvm_supported_mem_attributes(struct 
> > > kvm *kvm)
> > >   return 0;
> > >  }
> > >
> > > +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);
> > > +}
> > > +
> > >  static int kvm_vm_ioctl_set_mem_attributes(struct kvm *kvm,
> > >                                      struct kvm_memory_attributes *attrs)
> > >  {
> > >   gfn_t start, end;
> > >   unsigned long i;
> > >   void *entry;
> > > + int idx;
> > >   u64 supported_attrs = kvm_supported_mem_attributes(kvm);
> > >
> > > - /* flags is currently not used. */
> > > + /* 'flags' is currently not used. */
> > >   if (attrs->flags)
> > >           return -EINVAL;
> > >   if (attrs->attributes & ~supported_attrs)
> > > @@ -2372,6 +2409,13 @@ static int kvm_vm_ioctl_set_mem_attributes(struct 
> > > kvm *kvm,
> > >
> > >   entry = attrs->attributes ? xa_mk_value(attrs->attributes) : NULL;
> > >
> > > + if (kvm_arch_has_private_mem(kvm)) {
> > > +         KVM_MMU_LOCK(kvm);
> > > +         kvm_mmu_invalidate_begin(kvm);
> > > +         kvm_mmu_invalidate_range_add(kvm, start, end);
> >
> > Nit: this works for KVM_MEMORY_ATTRIBUTE_PRIVATE, but
> > the invalidation should be necessary yet for attribute change of:
> >
> > KVM_MEMORY_ATTRIBUTE_READ
> > KVM_MEMORY_ATTRIBUTE_WRITE
> > KVM_MEMORY_ATTRIBUTE_EXECUTE
>
> The unmapping is only needed for confidential usages which uses
> KVM_MEMORY_ATTRIBUTE_PRIVATE only and the other flags are defined here
> for other usages like pKVM. As Fuad commented in a different reply, pKVM
> supports in-place remapping and unmapping is unnecessary.

Ah, I see. It's fine to me, thanks.

>
> Thanks,
> Chao
> >
> > > +         KVM_MMU_UNLOCK(kvm);
> > > + }
> > > +
> > >   mutex_lock(&kvm->lock);
> > >   for (i = start; i < end; i++)
> > >           if (xa_err(xa_store(&kvm->mem_attr_array, i, entry,
> > > @@ -2379,6 +2423,16 @@ static int kvm_vm_ioctl_set_mem_attributes(struct 
> > > kvm *kvm,
> > >                   break;
> > >   mutex_unlock(&kvm->lock);
> > >
> > > + if (kvm_arch_has_private_mem(kvm)) {
> > > +         idx = srcu_read_lock(&kvm->srcu);
> > > +         KVM_MMU_LOCK(kvm);
> > > +         if (i > start)
> > > +                 kvm_unmap_mem_range(kvm, start, i);
> > > +         kvm_mmu_invalidate_end(kvm);
> >
> > Ditto.
> >
> > > +         KVM_MMU_UNLOCK(kvm);
> > > +         srcu_read_unlock(&kvm->srcu, idx);
> > > + }
> > > +
> > >   attrs->address = i << PAGE_SHIFT;
> > >   attrs->size = (end - i) << PAGE_SHIFT;
> > >
> > > --
> > > 2.25.1
> > >
> > >