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

Peter Xu
2020-02-06T16:26:26Z

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@arm.com>
> Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> ---
> 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@redhat.com>

>
> - 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