Re: [PATCH v2 01/15] KVM: Reinstall old memslots if arch preparation fails

Christoffer Dall
2019-10-23T09:29:07Z

On Mon, Oct 21, 2019 at 05:35:23PM -0700, Sean Christopherson wrote:
> Reinstall the old memslots if preparing the new memory region fails
> after invalidating a to-be-{re}moved memslot.
>
> Remove the superfluous 'old_memslots' variable so that it's somewhat
> clear that the error handling path needs to free the unused memslots,
> not simply the 'old' memslots.
>
> Fixes: bc6678a33d9b9 ("KVM: introduce kvm->srcu and convert kvm_set_memory_region to SRCU update")
> Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> ---
> virt/kvm/kvm_main.c | 23 ++++++++++++-----------
> 1 file changed, 12 insertions(+), 11 deletions(-)
>
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 67ef3f2e19e8..9afd706dc038 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -924,7 +924,7 @@ 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 = NULL, *old_memslots;
> + struct kvm_memslots *slots;
> int as_id, id;
> enum kvm_mr_change change;
>
> @@ -1032,7 +1032,13 @@ int __kvm_set_memory_region(struct kvm *kvm,
> slot = id_to_memslot(slots, id);
> slot->flags |= KVM_MEMSLOT_INVALID;
>
> - old_memslots = install_new_memslots(kvm, as_id, slots);
> + /*
> + * 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.
> @@ -1042,13 +1048,6 @@ int __kvm_set_memory_region(struct kvm *kvm,
> * - kvm_is_visible_gfn (mmu_check_roots)
> */
> kvm_arch_flush_shadow_memslot(kvm, slot);
> -
> - /*
> - * We can re-use the old_memslots from above, the only difference
> - * from the currently installed memslots is the invalid flag. This
> - * will get overwritten by update_memslots anyway.
> - */
> - slots = old_memslots;
> }
>
> r = kvm_arch_prepare_memory_region(kvm, &new, mem, change);
> @@ -1062,15 +1061,17 @@ int __kvm_set_memory_region(struct kvm *kvm,
> }
>
> update_memslots(slots, &new, change);
> - old_memslots = install_new_memslots(kvm, as_id, slots);
> + slots = install_new_memslots(kvm, as_id, slots);
>
> kvm_arch_commit_memory_region(kvm, mem, &old, &new, change);
>
> kvm_free_memslot(kvm, &old, &new);
> - kvfree(old_memslots);
> + 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_free:
> kvm_free_memslot(kvm, &new, &old);
> --
> 2.22.0

Reviewed-by: Christoffer Dall <christoffer.dall@arm.com>