Re: [PATCH v5 11/13] KVM: Zap existing KVM mappings when pages changed in the private fd

[Sean Christopherson]

On Thu, Mar 10, 2022, Chao Peng wrote:
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 67349421eae3..52319f49d58a 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -841,8 +841,43 @@ static int kvm_init_mmu_notifier(struct kvm *kvm)
>  #endif /* CONFIG_MMU_NOTIFIER && KVM_ARCH_WANT_MMU_NOTIFIER */
>  
>  #ifdef CONFIG_MEMFILE_NOTIFIER
> +static void kvm_memfile_notifier_handler(struct memfile_notifier *notifier,
> +                                      pgoff_t start, pgoff_t end)
> +{
> +     int idx;
> +     struct kvm_memory_slot *slot = container_of(notifier,
> +                                                 struct kvm_memory_slot,
> +                                                 notifier);
> +     struct kvm_gfn_range gfn_range = {
> +             .slot           = slot,
> +             .start          = start - (slot->private_offset >> PAGE_SHIFT),
> +             .end            = end - (slot->private_offset >> PAGE_SHIFT),
> +             .may_block      = true,
> +     };
> +     struct kvm *kvm = slot->kvm;
> +
> +     gfn_range.start = max(gfn_range.start, slot->base_gfn);
> +     gfn_range.end = min(gfn_range.end, slot->base_gfn + slot->npages);
> +
> +     if (gfn_range.start >= gfn_range.end)
> +             return;
> +
> +     idx = srcu_read_lock(&kvm->srcu);
> +     KVM_MMU_LOCK(kvm);
> +     kvm_unmap_gfn_range(kvm, &gfn_range);
> +     kvm_flush_remote_tlbs(kvm);

This should check the result of kvm_unmap_gfn_range() and flush only if 
necessary.

kvm->mmu_notifier_seq needs to be incremented, otherwise KVM will incorrectly
install a SPTE if the mapping is zapped between retrieving the pfn in faultin 
and
installing it after acquire mmu_lock.


> +     KVM_MMU_UNLOCK(kvm);
> +     srcu_read_unlock(&kvm->srcu, idx);
> +}
> +
> +static struct memfile_notifier_ops kvm_memfile_notifier_ops = {
> +     .invalidate = kvm_memfile_notifier_handler,
> +     .fallocate = kvm_memfile_notifier_handler,
> +};
> +
>  static inline int kvm_memfile_register(struct kvm_memory_slot *slot)
>  {
> +     slot->notifier.ops = &kvm_memfile_notifier_ops;
>       return memfile_register_notifier(file_inode(slot->private_file),
>                                        &slot->notifier,
>                                        &slot->pfn_ops);
> @@ -1963,6 +1998,7 @@ int __kvm_set_memory_region(struct kvm *kvm,
>       new->private_file = file;
>       new->private_offset = mem->flags & KVM_MEM_PRIVATE ?
>                             region_ext->private_offset : 0;
> +     new->kvm = kvm;
>  
>       r = kvm_set_memslot(kvm, old, new, change);
>       if (!r)
> -- 
> 2.17.1
>