Re: [PATCH RFCv1 6/8] kvm: Add helper kvm_dirty_ring_init()

[Juan Quintela <quintela@redhat.com>]

Gavin Shan <gshan@redhat.com> wrote:
> Due to multiple capabilities associated with the dirty ring for different
> architectures: KVM_CAP_DIRTY_{LOG_RING, LOG_RING_ACQ_REL} for x86 and
> arm64 separately. There will be more to be done in order to support the
> dirty ring for arm64.
>
> Lets add helper kvm_dirty_ring_init() to enable the dirty ring. With this,
> the code looks a bit clean.
>
> No functional change intended.
>
> Signed-off-by: Gavin Shan <gshan@redhat.com>
> ---
>  accel/kvm/kvm-all.c | 73 ++++++++++++++++++++++++++++-----------------
>  1 file changed, 46 insertions(+), 27 deletions(-)
>
> diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
> index 9ec117c441..399ef0f7e6 100644
> --- a/accel/kvm/kvm-all.c
> +++ b/accel/kvm/kvm-all.c
> @@ -1476,6 +1476,49 @@ static int kvm_dirty_ring_reaper_init(KVMState *s)
>      return 0;
>  }
>  
> +static int kvm_dirty_ring_init(KVMState *s)
> +{
> +    uint64_t ring_bytes;
> +    int ret;
> +
> +    /*
> +     * Read the max supported pages. Fall back to dirty logging mode
> +     * if the dirty ring isn't supported.
> +     */
> +    ret = kvm_vm_check_extension(s, KVM_CAP_DIRTY_LOG_RING);
> +    if (ret <= 0) {
> +        warn_report("KVM dirty ring not available, using bitmap method");
> +        s->kvm_dirty_ring_size = 0;
> +        return 0;
> +    }
> +
> +    ring_bytes = s->kvm_dirty_ring_size * sizeof(struct kvm_dirty_gfn);
> +    if (ring_bytes > ret) {
> +        error_report("KVM dirty ring size %" PRIu32 " too big "
> +                     "(maximum is %ld).  Please use a smaller value.",
> +                     s->kvm_dirty_ring_size,
> +                     (long)ret / sizeof(struct kvm_dirty_gfn));
> +        ret = -EINVAL;
> +        goto out;
> +    }
> +
> +    ret = kvm_vm_enable_cap(s, KVM_CAP_DIRTY_LOG_RING, 0, ring_bytes);
> +    if (ret) {
> +        error_report("Enabling of KVM dirty ring failed: %s. "
> +                     "Suggested minimum value is 1024.", strerror(-ret));
> +        ret = -EIO;
> +    }
> +
> +out:
> +    if (ret) {
> +        s->kvm_dirty_ring_size = 0;
> +    } else {
> +        s->kvm_dirty_ring_bytes = ring_bytes;
> +    }
> +
> +    return ret;
> +}

If you split it, you don't need the goto.

static int kvm_dirty_ring_init(KVMState *s)
{
    s->kvm_dirty_ring_size = 0;
    /*
     * Read the max supported pages. Fall back to dirty logging mode
     * if the dirty ring isn't supported.
     */
    int ret = kvm_vm_check_extension(s, KVM_CAP_DIRTY_LOG_RING);
    if (ret <= 0) {
        warn_report("KVM dirty ring not available, using bitmap method");
        return 0;
    }

    uint64_t ring_bytes = s->kvm_dirty_ring_size * sizeof(struct kvm_dirty_gfn);
    if (ring_bytes > ret) {
        error_report("KVM dirty ring size %" PRIu32 " too big "
                     "(maximum is %ld).  Please use a smaller value.",
                     s->kvm_dirty_ring_size,
                     (long)ret / sizeof(struct kvm_dirty_gfn));
        return -EINVAL;
    }

    ret = kvm_vm_enable_cap(s, KVM_CAP_DIRTY_LOG_RING, 0, ring_bytes);
    if (ret) {
        error_report("Enabling of KVM dirty ring failed: %s. "
                     "Suggested minimum value is 1024.", strerror(-ret));
        return -EIO;
    }

    s->kvm_dirty_ring_bytes = ring_bytes;
    return ret;
}



> +
>  static void kvm_region_add(MemoryListener *listener,
>                             MemoryRegionSection *section)
>  {
> @@ -2545,33 +2588,9 @@ static int kvm_init(MachineState *ms)
>       * dirty logging mode
>       */
>      if (s->kvm_dirty_ring_size > 0) {
> -        uint64_t ring_bytes;
> -
> -        ring_bytes = s->kvm_dirty_ring_size * sizeof(struct kvm_dirty_gfn);
> -
> -        /* Read the max supported pages */
> -        ret = kvm_vm_check_extension(s, KVM_CAP_DIRTY_LOG_RING);
> -        if (ret > 0) {
> -            if (ring_bytes > ret) {
> -                error_report("KVM dirty ring size %" PRIu32 " too big "
> -                             "(maximum is %ld).  Please use a smaller value.",
> -                             s->kvm_dirty_ring_size,
> -                             (long)ret / sizeof(struct kvm_dirty_gfn));
> -                ret = -EINVAL;
> -                goto err;
> -            }
> -
> -            ret = kvm_vm_enable_cap(s, KVM_CAP_DIRTY_LOG_RING, 0, ring_bytes);
> -            if (ret) {
> -                error_report("Enabling of KVM dirty ring failed: %s. "
> -                             "Suggested minimum value is 1024.", strerror(-ret));
> -                goto err;
> -            }
> -
> -            s->kvm_dirty_ring_bytes = ring_bytes;
> -         } else {
> -             warn_report("KVM dirty ring not available, using bitmap method");
> -             s->kvm_dirty_ring_size = 0;
> +        ret = kvm_dirty_ring_init(s);
> +        if (ret < 0) {
> +            goto err;
>          }
>      }