From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 478313EDE7A; Mon, 6 Jul 2026 07:28:55 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783322939; cv=none; b=aY08DfFbBC4sDYFhukbWkNbIbaI6AOW7HCCpI1NnyjQ0xqv84IAMJMNk759BZ0TIUY38eP3zKihs1M4MhxRYmfm+rimAL/QK84vNH3Qsv+h+9hkqJfsWXkhQ985jEB9tlsJFWWpGMFalX0DNmk7tWYmb3+b4Mg2ebI8dJwTExo8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783322939; c=relaxed/simple; bh=2xPZLCyu6U8/zbE8Zx5Ha8xuBUEk3fl2YhDFeyYX9AE=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=u+PRDFMWMMk0BFl96CsATD/3xYZ5Yy+sFt7E+F/SzRTyqw5pyap1dirGUNJvQXOZ/cvWmbfnHJ3kkm5ydWpdH1HP+Wrz3e49WwMryB0PHHBsLE7AEuohIl33RtO4TFXu78ASfZUk9/aQ9ay6LFjp6KV2J9EF59s8f1Id1auWpMA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=AlPLbPc8; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="AlPLbPc8" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4B1851F000E9; Mon, 6 Jul 2026 07:28:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1783322934; bh=HkDczeYQYsOmrsz59HCm+BoyWNh+mF0I2Z4wZmf+oWE=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=AlPLbPc8Yfr2j/WCNcgTwHSHw/i7+X0DXty0U49Tq72Lc0AdLcqqFJ7Rok1WYRYEt wZP7ebXK3WT0r/Q6ee9ax6gZTpI7P89CbjqaU1V/kNthYVxWGZE3SmdHPTBvPIifa6 avYbw768X3XCK3u2XGvtaI4Cnncjnya3KAUg3KNpSFzp0WAzWRF9hu24RiUrnP+JeL qBwFSWy+SgYEjPl7OJ9DZZ7qH7rZVy2Zbs34BUi12yIKNIOjJQ+03vaJc4WS4jzPpC /vopDOanG3puM7wXBbrow1Xw3Hi15h8l2nwJyFRHMYvi8rXWJXVjgpdaB1loG6FKlp I6gwFmozL6dSQ== Message-ID: <13794c5e-375a-4fc5-84b4-a637d077f8a0@kernel.org> Date: Mon, 6 Jul 2026 09:28:50 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] virtio_balloon: prime stats vq after virtio_device_ready() To: "Michael S. Tsirkin" , linux-kernel@vger.kernel.org Cc: Jason Wang , Xuan Zhuo , =?UTF-8?Q?Eugenio_P=C3=A9rez?= , Adam Litke , Rusty Russell , virtualization@lists.linux.dev, Andrew Morton , linux-mm@kvack.org References: <2f0d0de033f3005d3b985883be3e5cf37b3f6c42.1783278596.git.mst@redhat.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzS5EYXZpZCBIaWxk ZW5icmFuZCAoQ3VycmVudCkgPGRhdmlkQGtlcm5lbC5vcmc+wsGQBBMBCAA6AhsDBQkmWAik AgsJBBUKCQgCFgICHgUCF4AWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaYJt/AIZAQAKCRBN 3hD3AP+DWriiD/9BLGEKG+N8L2AXhikJg6YmXom9ytRwPqDgpHpVg2xdhopoWdMRXjzOrIKD g4LSnFaKneQD0hZhoArEeamG5tyo32xoRsPwkbpIzL0OKSZ8G6mVbFGpjmyDLQCAxteXCLXz ZI0VbsuJKelYnKcXWOIndOrNRvE5eoOfTt2XfBnAapxMYY2IsV+qaUXlO63GgfIOg8RBaj7x 3NxkI3rV0SHhI4GU9K6jCvGghxeS1QX6L/XI9mfAYaIwGy5B68kF26piAVYv/QZDEVIpo3t7 /fjSpxKT8plJH6rhhR0epy8dWRHk3qT5tk2P85twasdloWtkMZ7FsCJRKWscm1BLpsDn6EQ4 jeMHECiY9kGKKi8dQpv3FRyo2QApZ49NNDbwcR0ZndK0XFo15iH708H5Qja/8TuXCwnPWAcJ DQoNIDFyaxe26Rx3ZwUkRALa3iPcVjE0//TrQ4KnFf+lMBSrS33xDDBfevW9+Dk6IISmDH1R HFq2jpkN+FX/PE8eVhV68B2DsAPZ5rUwyCKUXPTJ/irrCCmAAb5Jpv11S7hUSpqtM/6oVESC 3z/7CzrVtRODzLtNgV4r5EI+wAv/3PgJLlMwgJM90Fb3CB2IgbxhjvmB1WNdvXACVydx55V7 LPPKodSTF29rlnQAf9HLgCphuuSrrPn5VQDaYZl4N/7zc2wcWM7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: <2f0d0de033f3005d3b985883be3e5cf37b3f6c42.1783278596.git.mst@redhat.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 7/5/26 21:12, Michael S. Tsirkin wrote: > The virtio spec requires the driver not to kick the device before > DRIVER_OK is set. init_vqs() primes the stats virtqueue with a buffer > and kicks the device before virtio_device_ready() is called in > virtballoon_probe(), violating this requirement. > > Further, if the device responds to the early kick by processing the > buffer before DRIVER_OK, stats_request() fires and queues > update_balloon_stats_work. Should probe then fail and free vb, the work > runs against freed memory. > > To fix, move buffer setup to after DRIVER_OK. Be careful to > disable update_balloon_stats_work while this is going on, > to make sure it does not race with the setup. > > setup_vqs() warns but does not fail probe or restore if > virtqueue_add_outbuf() fails; the call never actually fails in these > contexts since the queue is freshly initialized and empty. > > Testing: tested that stats still work after the change. > > Fixes: 9564e138b1f6 ("virtio: Add memory statistics reporting to the balloon driver (V4)") > Reported-by: Sashiko:gemini-3.1-pro-preview > Cc: David Hildenbrand > Assisted-by: Claude:claude-sonnet-4-6 > Signed-off-by: Michael S. Tsirkin > --- > > changes from v1: > check that work enable/disable is balanced > explain how add buf never fails in probe/restore > > drivers/virtio/virtio_balloon.c | 50 +++++++++++++++++++++------------ > 1 file changed, 32 insertions(+), 18 deletions(-) > > diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c > index 088b3a0e6ce6..bc0a2b19ca7d 100644 > --- a/drivers/virtio/virtio_balloon.c > +++ b/drivers/virtio/virtio_balloon.c > @@ -611,25 +611,8 @@ static int init_vqs(struct virtio_balloon *vb) > vb->inflate_vq = vqs[VIRTIO_BALLOON_VQ_INFLATE]; > vb->deflate_vq = vqs[VIRTIO_BALLOON_VQ_DEFLATE]; > if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ)) { > - struct scatterlist sg; > - unsigned int num_stats; > vb->stats_vq = vqs[VIRTIO_BALLOON_VQ_STATS]; > - > - /* > - * Prime this virtqueue with one buffer so the hypervisor can > - * use it to signal us later (it can't be broken yet!). > - */ > - num_stats = update_balloon_stats(vb); > - > - sg_init_one(&sg, vb->stats, sizeof(vb->stats[0]) * num_stats); > - err = virtqueue_add_outbuf(vb->stats_vq, &sg, 1, vb, > - GFP_KERNEL); > - if (err) { > - dev_warn(&vb->vdev->dev, "%s: add stat_vq failed\n", > - __func__); > - return err; > - } > - virtqueue_kick(vb->stats_vq); > + disable_work(&vb->update_balloon_stats_work); That's to stop the stats queue triggering stats_request() I assume? Is that valid before we actually added+kicked ourselves? Also, can't we simply handle that in stats_request(), just ignoring it there? Then we wouldn't have to go through the siable + enable. > } > > if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT)) > @@ -916,6 +899,33 @@ static int virtio_balloon_register_shrinker(struct virtio_balloon *vb) > return 0; > } > > +static void setup_vqs(struct virtio_balloon *vb) > +{ > + struct scatterlist sg; > + unsigned int num_stats; > + bool ret; > + > + if (!virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ)) > + return; > + > + /* > + * Prime this virtqueue with one buffer so the hypervisor can > + * use it to signal us later (it can't be broken yet!). > + */ > + num_stats = update_balloon_stats(vb); > + sg_init_one(&sg, vb->stats, sizeof(vb->stats[0]) * num_stats); > + if (virtqueue_add_outbuf(vb->stats_vq, &sg, 1, vb, GFP_KERNEL)) { > + dev_warn(&vb->vdev->dev, "%s: add stat_vq failed\n", __func__); > + return; > + } > + virtqueue_kick(vb->stats_vq); > + > + ret = enable_and_queue_work(system_freezable_wq, > + &vb->update_balloon_stats_work); > + /* Make sure we balanced enable/disable, or we won't report stats. */ > + BUG_ON(!ret); A WARN_ON_ONCE() should be good enough here, no need to crash the kernel (no new BUG_ON's). -- Cheers, David