From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id EABA453B4 for ; Sun, 17 Sep 2023 19:34:44 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4ADCAC433C7; Sun, 17 Sep 2023 19:34:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1694979284; bh=N+aFPQtEAASxr/DqdlhsAdqbX/l75KZtxABfuz6jWcU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=OaccUs2jYdqjBY8eFq59PXdHH3Wf0oMGzbpV+uSkJ/V3tAwlMci1UJ4rPQTvmQUYX 7+gzVLt3ckBtvZKbyBw69R1PPcGLrFAOP+uSCibJ/Hvbhu3ZJEQMel99RdVL0R3ncg Y2gqSe+Ou40RiRUngF3bSaNWbrRgCyZahfrc7tRI= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Yuan Yao , Jason Wang , "Michael S. Tsirkin" , Sasha Levin Subject: [PATCH 5.10 267/406] virtio_ring: fix avail_wrap_counter in virtqueue_add_packed Date: Sun, 17 Sep 2023 21:12:01 +0200 Message-ID: <20230917191108.283053287@linuxfoundation.org> X-Mailer: git-send-email 2.42.0 In-Reply-To: <20230917191101.035638219@linuxfoundation.org> References: <20230917191101.035638219@linuxfoundation.org> User-Agent: quilt/0.67 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 5.10-stable review patch. If anyone has any objections, please let me know. ------------------ From: Yuan Yao [ Upstream commit 1acfe2c1225899eab5ab724c91b7e1eb2881b9ab ] In current packed virtqueue implementation, the avail_wrap_counter won't flip, in the case when the driver supplies a descriptor chain with a length equals to the queue size; total_sg == vq->packed.vring.num. Let’s assume the following situation: vq->packed.vring.num=4 vq->packed.next_avail_idx: 1 vq->packed.avail_wrap_counter: 0 Then the driver adds a descriptor chain containing 4 descriptors. We expect the following result with avail_wrap_counter flipped: vq->packed.next_avail_idx: 1 vq->packed.avail_wrap_counter: 1 But, the current implementation gives the following result: vq->packed.next_avail_idx: 1 vq->packed.avail_wrap_counter: 0 To reproduce the bug, you can set a packed queue size as small as possible, so that the driver is more likely to provide a descriptor chain with a length equal to the packed queue size. For example, in qemu run following commands: sudo qemu-system-x86_64 \ -enable-kvm \ -nographic \ -kernel "path/to/kernel_image" \ -m 1G \ -drive file="path/to/rootfs",if=none,id=disk \ -device virtio-blk,drive=disk \ -drive file="path/to/disk_image",if=none,id=rwdisk \ -device virtio-blk,drive=rwdisk,packed=on,queue-size=4,\ indirect_desc=off \ -append "console=ttyS0 root=/dev/vda rw init=/bin/bash" Inside the VM, create a directory and mount the rwdisk device on it. The rwdisk will hang and mount operation will not complete. This commit fixes the wrap counter error by flipping the packed.avail_wrap_counter, when start of descriptor chain equals to the end of descriptor chain (head == i). Fixes: 1ce9e6055fa0 ("virtio_ring: introduce packed ring support") Signed-off-by: Yuan Yao Message-Id: <20230808051110.3492693-1-yuanyaogoog@chromium.org> Acked-by: Jason Wang Signed-off-by: Michael S. Tsirkin Signed-off-by: Sasha Levin --- drivers/virtio/virtio_ring.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c index 3cc2a4ee7152c..cf0e8e1893ee6 100644 --- a/drivers/virtio/virtio_ring.c +++ b/drivers/virtio/virtio_ring.c @@ -1190,7 +1190,7 @@ static inline int virtqueue_add_packed(struct virtqueue *_vq, } } - if (i < head) + if (i <= head) vq->packed.avail_wrap_counter ^= 1; /* We're using some buffers from the free list. */ -- 2.40.1