linux-kernel - Re: [PATCH] virtio: Honour 'may_reduce_num' in vring_create

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Date:   Mon, 8 Apr 2019 15:32:38 +0200
From:   Jens Freimann <jfreimann@...hat.com>
To:     Cornelia Huck <cohuck@...hat.com>
Cc:     "Michael S . Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        virtualization@...ts.linux-foundation.org,
        Halil Pasic <pasic@...ux.ibm.com>
Subject: Re: [PATCH] virtio: Honour 'may_reduce_num' in vring_create_virtqueue

On Mon, Apr 08, 2019 at 02:33:22PM +0200, Cornelia Huck wrote:
>vring_create_virtqueue() allows the caller to specify via the
>may_reduce_num parameter whether the vring code is allowed to
>allocate a smaller ring than specified.
>
>However, the split ring allocation code tries to allocate a
>smaller ring on allocation failure regardless of what the
>caller specified. This may cause trouble for e.g. virtio-pci
>in legacy mode, which does not support ring resizing. (The
>packed ring code does not resize in any case.)
>
>Let's fix this by bailing out immediately in the split ring code
>if the requested size cannot be allocated and may_reduce_num has
>not been specified.
>
>While at it, fix a typo in the usage instructions.
>
>Fixes: 2a2d1382fe9d ("virtio: Add improved queue allocation API")
>Cc: stable@...r.kernel.org # v4.6+
>Signed-off-by: Cornelia Huck <cohuck@...hat.com>
>---
> drivers/virtio/virtio_ring.c | 2 ++
> include/linux/virtio_ring.h  | 2 +-
> 2 files changed, 3 insertions(+), 1 deletion(-)
>

Reviewed-by: Jens Freimann <jfreimann@...hat.com>