Re: [Qemu-devel] [PATCH 3/4] virtio-ccw: feature bits > 31 handling

[David Hildenbrand]

> We currently switch off the VERSION_1 feature bit if the guest has
> not negotiated at least revision 1. As no feature bits beyond 31 are
> valid however unless VERSION_1 has been negotiated, make sure that
> legacy guests never see a feature bit beyond 31.
> 
> Signed-off-by: Cornelia Huck 
> ---
>  hw/s390x/virtio-ccw.c | 21 -
>  1 file changed, 8 insertions(+), 13 deletions(-)
> 
> diff --git a/hw/s390x/virtio-ccw.c b/hw/s390x/virtio-ccw.c
> index 85e2a5d..eed7b3e 100644
> --- a/hw/s390x/virtio-ccw.c
> +++ b/hw/s390x/virtio-ccw.c
> @@ -468,15 +468,12 @@ static int virtio_ccw_cb(SubchDev *sch, CCW1 ccw)
>  NULL);
>  if (features.index == 0) {
>  features.features = (uint32_t)vdev->host_features;
> -} else if (features.index == 1) {
> -features.features = (uint32_t)(vdev->host_features >> 32);
> +} else if ((features.index == 1) && (dev->revision >= 1)) {
>  /*
> - * Don't offer version 1 to the guest if it did not
> - * negotiate at least revision 1.
> + * Only offer feature bits beyond 31 if the guest has
> + * negotiated at least revision 1.
>   */
> -if (dev->revision <= 0) {
> -features.features &= ~(1 << (VIRTIO_F_VERSION_1 - 32));
> -}
> +features.features = (uint32_t)(vdev->host_features >> 32);
>  } else {
>  /* Return zeroes if the guest supports more feature bits. */
>  features.features = 0;
> @@ -515,14 +512,12 @@ static int virtio_ccw_cb(SubchDev *sch, CCW1 ccw)
>  virtio_set_features(vdev,
>  (vdev->guest_features & 
> 0xULL) |
>  features.features);
> -} else if (features.index == 1) {
> +} else if ((features.index == 1) && (dev->revision >= 1)) {
>  /*
> - * The guest should not set version 1 if it didn't
> - * negotiate a revision >= 1.
> + * If the guest did not negotiate at least revision 1,
> + * we did not offer it any feature bits beyond 31. Such a
> + * guest passing us any bit here is therefore buggy.
>   */
> -if (dev->revision <= 0) {
> -features.features &= ~(1 << (VIRTIO_F_VERSION_1 - 32));
> -}
>  virtio_set_features(vdev,
>  (vdev->guest_features & 
> 0xULL) |
>  ((uint64_t)features.features << 32));

Looks sane to me!

Reviewed-by: David Hildenbrand 

David

[Qemu-devel] [PATCH 3/4] virtio-ccw: feature bits > 31 handling

[Cornelia Huck]

We currently switch off the VERSION_1 feature bit if the guest has
not negotiated at least revision 1. As no feature bits beyond 31 are
valid however unless VERSION_1 has been negotiated, make sure that
legacy guests never see a feature bit beyond 31.

Signed-off-by: Cornelia Huck 
---
 hw/s390x/virtio-ccw.c | 21 -
 1 file changed, 8 insertions(+), 13 deletions(-)

diff --git a/hw/s390x/virtio-ccw.c b/hw/s390x/virtio-ccw.c
index 85e2a5d..eed7b3e 100644
--- a/hw/s390x/virtio-ccw.c
+++ b/hw/s390x/virtio-ccw.c
@@ -468,15 +468,12 @@ static int virtio_ccw_cb(SubchDev *sch, CCW1 ccw)
 NULL);
 if (features.index == 0) {
 features.features = (uint32_t)vdev->host_features;
-} else if (features.index == 1) {
-features.features = (uint32_t)(vdev->host_features >> 32);
+} else if ((features.index == 1) && (dev->revision >= 1)) {
 /*
- * Don't offer version 1 to the guest if it did not
- * negotiate at least revision 1.
+ * Only offer feature bits beyond 31 if the guest has
+ * negotiated at least revision 1.
  */
-if (dev->revision <= 0) {
-features.features &= ~(1 << (VIRTIO_F_VERSION_1 - 32));
-}
+features.features = (uint32_t)(vdev->host_features >> 32);
 } else {
 /* Return zeroes if the guest supports more feature bits. */
 features.features = 0;
@@ -515,14 +512,12 @@ static int virtio_ccw_cb(SubchDev *sch, CCW1 ccw)
 virtio_set_features(vdev,
 (vdev->guest_features & 
0xULL) |
 features.features);
-} else if (features.index == 1) {
+} else if ((features.index == 1) && (dev->revision >= 1)) {
 /*
- * The guest should not set version 1 if it didn't
- * negotiate a revision >= 1.
+ * If the guest did not negotiate at least revision 1,
+ * we did not offer it any feature bits beyond 31. Such a
+ * guest passing us any bit here is therefore buggy.
  */
-if (dev->revision <= 0) {
-features.features &= ~(1 << (VIRTIO_F_VERSION_1 - 32));
-}
 virtio_set_features(vdev,
 (vdev->guest_features & 
0xULL) |
 ((uint64_t)features.features << 32));
-- 
2.3.8