Re: [PATCH v5 09/19] KVM: Move setting of memslot into helper routine

[Peter Xu]

On Tue, Jan 21, 2020 at 02:31:47PM -0800, Sean Christopherson wrote:
> Split out the core functionality of setting a memslot into a separate
> helper in preparation for moving memslot deletion into its own routine.
> 
> Tested-by: Christoffer Dall <christoffer.dall@xxxxxxx>
> Reviewed-by: Philippe Mathieu-Daudà <f4bug@xxxxxxxxx>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
> ---
>  virt/kvm/kvm_main.c | 106 ++++++++++++++++++++++++++------------------
>  1 file changed, 63 insertions(+), 43 deletions(-)
> 
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index fdf045a5d240..64f6c5d35260 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -982,6 +982,66 @@ static struct kvm_memslots *install_new_memslots(struct kvm *kvm,
>  	return old_memslots;
>  }
>  
> +static int kvm_set_memslot(struct kvm *kvm,
> +			   const struct kvm_userspace_memory_region *mem,
> +			   const struct kvm_memory_slot *old,
> +			   struct kvm_memory_slot *new, int as_id,
> +			   enum kvm_mr_change change)
> +{
> +	struct kvm_memory_slot *slot;
> +	struct kvm_memslots *slots;
> +	int r;
> +
> +	slots = kvzalloc(sizeof(struct kvm_memslots), GFP_KERNEL_ACCOUNT);
> +	if (!slots)
> +		return -ENOMEM;
> +	memcpy(slots, __kvm_memslots(kvm, as_id), sizeof(struct kvm_memslots));
> +
> +	if (change == KVM_MR_DELETE || change == KVM_MR_MOVE) {
> +		/*
> +		 * Note, the INVALID flag needs to be in the appropriate entry
> +		 * in the freshly allocated memslots, not in @old or @new.
> +		 */
> +		slot = id_to_memslot(slots, old->id);
> +		slot->flags |= KVM_MEMSLOT_INVALID;
> +
> +		/*
> +		 * We can re-use the old memslots, the only difference from the
> +		 * newly installed memslots is the invalid flag, which will get
> +		 * dropped by update_memslots anyway.  We'll also revert to the
> +		 * old memslots if preparing the new memory region fails.
> +		 */
> +		slots = install_new_memslots(kvm, as_id, slots);
> +
> +		/* From this point no new shadow pages pointing to a deleted,
> +		 * or moved, memslot will be created.
> +		 *
> +		 * validation of sp->gfn happens in:
> +		 *	- gfn_to_hva (kvm_read_guest, gfn_to_pfn)
> +		 *	- kvm_is_visible_gfn (mmu_check_root)
> +		 */
> +		kvm_arch_flush_shadow_memslot(kvm, slot);
> +	}
> +
> +	r = kvm_arch_prepare_memory_region(kvm, new, mem, change);
> +	if (r)
> +		goto out_slots;
> +
> +	update_memslots(slots, new, change);
> +	slots = install_new_memslots(kvm, as_id, slots);
> +
> +	kvm_arch_commit_memory_region(kvm, mem, old, new, change);
> +
> +	kvfree(slots);
> +	return 0;
> +
> +out_slots:
> +	if (change == KVM_MR_DELETE || change == KVM_MR_MOVE)
> +		slots = install_new_memslots(kvm, as_id, slots);
> +	kvfree(slots);
> +	return r;
> +}
> +
>  /*
>   * Allocate some memory and give it an address in the guest physical address
>   * space.
> @@ -998,7 +1058,6 @@ int __kvm_set_memory_region(struct kvm *kvm,
>  	unsigned long npages;
>  	struct kvm_memory_slot *slot;
>  	struct kvm_memory_slot old, new;
> -	struct kvm_memslots *slots;
>  	int as_id, id;
>  	enum kvm_mr_change change;
>  
> @@ -1085,58 +1144,19 @@ int __kvm_set_memory_region(struct kvm *kvm,
>  			return r;
>  	}
>  
> -	slots = kvzalloc(sizeof(struct kvm_memslots), GFP_KERNEL_ACCOUNT);
> -	if (!slots) {
> -		r = -ENOMEM;
> -		goto out_bitmap;
> -	}
> -	memcpy(slots, __kvm_memslots(kvm, as_id), sizeof(struct kvm_memslots));
> -
> -	if ((change == KVM_MR_DELETE) || (change == KVM_MR_MOVE)) {
> -		slot = id_to_memslot(slots, id);
> -		slot->flags |= KVM_MEMSLOT_INVALID;
> -
> -		/*
> -		 * We can re-use the old memslots, the only difference from the
> -		 * newly installed memslots is the invalid flag, which will get
> -		 * dropped by update_memslots anyway.  We'll also revert to the
> -		 * old memslots if preparing the new memory region fails.
> -		 */
> -		slots = install_new_memslots(kvm, as_id, slots);
> -
> -		/* From this point no new shadow pages pointing to a deleted,
> -		 * or moved, memslot will be created.
> -		 *
> -		 * validation of sp->gfn happens in:
> -		 *	- gfn_to_hva (kvm_read_guest, gfn_to_pfn)
> -		 *	- kvm_is_visible_gfn (mmu_check_root)
> -		 */
> -		kvm_arch_flush_shadow_memslot(kvm, slot);
> -	}
> -
> -	r = kvm_arch_prepare_memory_region(kvm, &new, mem, change);
> -	if (r)
> -		goto out_slots;
> -
>  	/* actual memory is freed via old in kvm_free_memslot below */
>  	if (change == KVM_MR_DELETE) {
>  		new.dirty_bitmap = NULL;
>  		memset(&new.arch, 0, sizeof(new.arch));
>  	}

It's not extremely clear to me on why this single block is leftover
here instead of putting into kvm_set_memslot().  I see that after all
it'll be removed in patch 12, so it seems OK:

Reviewed-by: Peter Xu <peterx@xxxxxxxxxx>

>  
> -	update_memslots(slots, &new, change);
> -	slots = install_new_memslots(kvm, as_id, slots);
> -
> -	kvm_arch_commit_memory_region(kvm, mem, &old, &new, change);
> +	r = kvm_set_memslot(kvm, mem, &old, &new, as_id, change);
> +	if (r)
> +		goto out_bitmap;
>  
>  	kvm_free_memslot(kvm, &old, &new);
> -	kvfree(slots);
>  	return 0;
>  
> -out_slots:
> -	if (change == KVM_MR_DELETE || change == KVM_MR_MOVE)
> -		slots = install_new_memslots(kvm, as_id, slots);
> -	kvfree(slots);
>  out_bitmap:
>  	if (new.dirty_bitmap && !old.dirty_bitmap)
>  		kvm_destroy_dirty_bitmap(&new);
> -- 
> 2.24.1
> 

-- 
Peter Xu