Re: [RFC PATCH 4/9] kvm_main.c: split logic in kvm_set_memslots

Paolo Bonzini
2022-09-28T17:04:50Z

On 9/9/22 12:45, Emanuele Giuseppe Esposito wrote:
> +/*
> + * Takes kvm->slots_arch_lock, and releases it only if
> + * invalid_slot allocation or kvm_prepare_memory_region failed.
> +*/

Much simpler: "kvm->slots_arch_lock is taken on a successful return."

This is a small change in phrasing, but it makes a lot more sense: on
success you are preparing for the final commit operation, otherwise you
just want the caller to return your errno value.

[...]

> +/* Must be called with kvm->slots_arch_lock held, but releases it. */
s/but/and/. Even better, "and releases it before returning". "But"
tells the reader that something strange is going on, "and" tells it that
something simple is going on.

I would also rename the functions along the lines of my review to patch
3, to highlight that these function prepare/commit a *change* to a memslot.

> +static void kvm_finish_memslot(struct kvm *kvm,
> + struct kvm_internal_memory_region_list *batch)
> +{
> + struct kvm_memory_slot *invalid_slot = batch->invalid;
> + struct kvm_memory_slot *old = batch->old;
> + struct kvm_memory_slot *new = batch->new;
> + enum kvm_mr_change change = batch->change;

lockdep_assert_held(&kvm->slots_arch_lock);

>
> /*
> * For DELETE and MOVE, the working slot is now active as the INVALID
> @@ -1883,6 +1898,18 @@ static int kvm_set_memslot(struct kvm *kvm,
> * responsible for knowing that new->arch may be stale.
> */
> kvm_commit_memory_region(kvm, batch);
> +}
> +
> +static int kvm_set_memslot(struct kvm *kvm,
> + struct kvm_internal_memory_region_list *batch)
> +{
> + int r;
> +
> + r = kvm_prepare_memslot(kvm, batch);
> + if (r)
> + return r;
> +
> + kvm_finish_memslot(kvm, batch);
>
> return 0;

Ok, these are the functions I hinted at in the review of the previous
patch, so we're not far away. You should be able to move the
kvm_set_memslot call to kvm_set_memory_region in patch 3, and then
replace it with the two calls here directly in kvm_set_memory_region.

Paolo