linux-kernel - [PATCH] vhost-vdpa: filter VIRTIO_F_RING

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Message-Id: <20230605110644.151211-1-sgarzare@redhat.com>
Date:   Mon,  5 Jun 2023 13:06:44 +0200
From:   Stefano Garzarella <sgarzare@...hat.com>
To:     virtualization@...ts.linux-foundation.org
Cc:     netdev@...r.kernel.org, Jason Wang <jasowang@...hat.com>,
        Eugenio Pérez <eperezma@...hat.com>,
        Tiwei Bie <tiwei.bie@...el.com>, kvm@...r.kernel.org,
        "Michael S. Tsirkin" <mst@...hat.com>, linux-kernel@...r.kernel.org
Subject: [PATCH] vhost-vdpa: filter VIRTIO_F_RING_PACKED feature

vhost-vdpa IOCTLs (eg. VHOST_GET_VRING_BASE, VHOST_SET_VRING_BASE)
don't support packed virtqueue well yet, so let's filter the
VIRTIO_F_RING_PACKED feature for now in vhost_vdpa_get_features().

This way, even if the device supports it, we don't risk it being
negotiated, then the VMM is unable to set the vring state properly.

Fixes: 4c8cf31885f6 ("vhost: introduce vDPA-based backend")
Cc: stable@...r.kernel.org
Signed-off-by: Stefano Garzarella <sgarzare@...hat.com>
---

Notes:
    This patch should be applied before the "[PATCH v2 0/3] vhost_vdpa:
    better PACKED support" series [1] and backported in stable branches.
    
    We can revert it when we are sure that everything is working with
    packed virtqueues.
    
    Thanks,
    Stefano
    
    [1] https://lore.kernel.org/virtualization/20230424225031.18947-1-shannon.nelson@amd.com/

 drivers/vhost/vdpa.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
index 8c1aefc865f0..ac2152135b23 100644
--- a/drivers/vhost/vdpa.c
+++ b/drivers/vhost/vdpa.c
@@ -397,6 +397,12 @@ static long vhost_vdpa_get_features(struct vhost_vdpa *v, u64 __user *featurep)
 
 	features = ops->get_device_features(vdpa);
 
+	/*
+	 * IOCTLs (eg. VHOST_GET_VRING_BASE, VHOST_SET_VRING_BASE) don't support
+	 * packed virtqueue well yet, so let's filter the feature for now.
+	 */
+	features &= ~BIT_ULL(VIRTIO_F_RING_PACKED);
+
 	if (copy_to_user(featurep, &features, sizeof(features)))
 		return -EFAULT;
 

base-commit: 9561de3a55bed6bdd44a12820ba81ec416e705a7
-- 
2.40.1