Re: [PATCH RFC] virtgpu: don't reset on shutdown

["Michael S. Tsirkin" <mst@redhat.com>]

On Thu, Apr 10, 2025 at 02:33:26PM +0200, Jocelyn Falempe wrote:
> On 10/04/2025 09:16, Michael S. Tsirkin wrote:
> > It looks like GPUs are used by panic after shutdown is invoked.
> > Thus, breaking virtio gpu in the shutdown callback is not a good idea -
> > guest hangs attempting to flush out the panics, with this warnings:
> 
> I don't think drm_panic is involved. In your backtrace, the warning
> comes from virtio_gpu_queue_ctrl_sgs(), which is called by fbcon, using drm
> fbdev emulation to draw the console.
> 
> In case of drm_panic, it is the panic variant,
> virtio_gpu_panic_queue_ctrl_sgs() which is called.
> 
> Also the line number is for the centos-stream-9 kernel, which don't have the
> "panic" variant of this function yet.
> 
> > 
> > [   20.504464] WARNING: CPU: 0 PID: 568 at drivers/gpu/drm/virtio/virtgpu_vq.c:358 virtio_gpu_queue_ctrl_sgs+0x236/0x290 [virtio_gpu]
> > [   20.505685] Modules linked in: nft_fib_inet nft_fib_ipv4 nft_fib_ipv6 nft_fib nft_reject_inet nf_reject_ipv4 nf_reject_ipv6 nft_reject nft_ct nft_chain_nat nf_nat nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 rfkill ip_set nf_tables nfnetlink vfat fat intel_rapl_msr intel_rapl_common intel_uncore_frequency_common nfit libnvdimm kvm_intel kvm rapl iTCO_wdt iTCO_vendor_support virtio_gpu virtio_dma_buf pcspkr drm_shmem_helper i2c_i801 drm_kms_helper lpc_ich i2c_smbus virtio_balloon joydev drm fuse xfs libcrc32c ahci libahci crct10dif_pclmul crc32_pclmul crc32c_intel libata virtio_net ghash_clmulni_intel net_failover virtio_blk failover serio_raw dm_mirror dm_region_hash dm_log dm_mod
> > [   20.511847] CPU: 0 PID: 568 Comm: kworker/0:3 Kdump: loaded Tainted: G        W         -------  ---  5.14.0-578.6675_1757216455.el9.x86_64 #1
> > [   20.513157] Hardware name: Red Hat KVM/RHEL, BIOS edk2-20241117-3.el9 11/17/2024
> > [   20.513918] Workqueue: events drm_fb_helper_damage_work [drm_kms_helper]
> > [   20.514626] RIP: 0010:virtio_gpu_queue_ctrl_sgs+0x236/0x290 [virtio_gpu]
> > [   20.515332] Code: 00 00 48 85 c0 74 0c 48 8b 78 08 48 89 ee e8 51 50 00 00 65 ff 0d 42 e3 74 3f 0f 85 69 ff ff ff 0f 1f 44 00 00 e9 5f ff ff ff <0f> 0b e9 3f ff ff ff 48 83 3c 24 00 74 0e 49 8b 7f 40 48 85 ff 74
> > [   20.517272] RSP: 0018:ff34f0a8c0787ad8 EFLAGS: 00010282
> > [   20.517820] RAX: 00000000fffffffb RBX: 0000000000000000 RCX: 0000000000000820
> > [   20.518565] RDX: 0000000000000000 RSI: ff34f0a8c0787be0 RDI: ff218bef03a26300
> > [   20.519308] RBP: ff218bef03a26300 R08: 0000000000000001 R09: ff218bef07224360
> > [   20.520059] R10: 0000000000008dc0 R11: 0000000000000002 R12: ff218bef02630028
> > [   20.520806] R13: ff218bef0263fb48 R14: ff218bef00cb8000 R15: ff218bef07224360
> > [   20.521555] FS:  0000000000000000(0000) GS:ff218bef7ba00000(0000) knlGS:0000000000000000
> > [   20.522397] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > [   20.522996] CR2: 000055ac4f7871c0 CR3: 000000010b9f2002 CR4: 0000000000771ef0
> > [   20.523740] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> > [   20.524477] DR3: 0000000000000000 DR6: 00000000fffe07f0 DR7: 0000000000000400
> > [   20.525223] PKRU: 55555554
> > [   20.525515] Call Trace:
> > [   20.525777]  <TASK>
> > [   20.526003]  ? show_trace_log_lvl+0x1c4/0x2df
> > [   20.526464]  ? show_trace_log_lvl+0x1c4/0x2df
> > [   20.526925]  ? virtio_gpu_queue_fenced_ctrl_buffer+0x82/0x2c0 [virtio_gpu]
> > [   20.527643]  ? virtio_gpu_queue_ctrl_sgs+0x236/0x290 [virtio_gpu]
> > [   20.528282]  ? __warn+0x7e/0xd0
> > [   20.528621]  ? virtio_gpu_queue_ctrl_sgs+0x236/0x290 [virtio_gpu]
> > [   20.529256]  ? report_bug+0x100/0x140
> > [   20.529643]  ? handle_bug+0x3c/0x70
> > [   20.530010]  ? exc_invalid_op+0x14/0x70
> > [   20.530421]  ? asm_exc_invalid_op+0x16/0x20
> > [   20.530862]  ? virtio_gpu_queue_ctrl_sgs+0x236/0x290 [virtio_gpu]
> > [   20.531506]  ? virtio_gpu_queue_ctrl_sgs+0x174/0x290 [virtio_gpu]
> > [   20.532148]  virtio_gpu_queue_fenced_ctrl_buffer+0x82/0x2c0 [virtio_gpu]
> > [   20.532843]  virtio_gpu_primary_plane_update+0x3e2/0x460 [virtio_gpu]
> > [   20.533520]  drm_atomic_helper_commit_planes+0x108/0x320 [drm_kms_helper]
> > [   20.534233]  drm_atomic_helper_commit_tail+0x45/0x80 [drm_kms_helper]
> > [   20.534914]  commit_tail+0xd2/0x130 [drm_kms_helper]
> > [   20.535446]  drm_atomic_helper_commit+0x11b/0x140 [drm_kms_helper]
> > [   20.536097]  drm_atomic_commit+0xa4/0xe0 [drm]
> > [   20.536588]  ? __pfx___drm_printfn_info+0x10/0x10 [drm]
> > [   20.537162]  drm_atomic_helper_dirtyfb+0x192/0x270 [drm_kms_helper]
> > [   20.537823]  drm_fbdev_shmem_helper_fb_dirty+0x43/0xa0 [drm_shmem_helper]
> > [   20.538536]  drm_fb_helper_damage_work+0x87/0x160 [drm_kms_helper]
> > [   20.539188]  process_one_work+0x194/0x380
> > [   20.539612]  worker_thread+0x2fe/0x410
> > [   20.540007]  ? __pfx_worker_thread+0x10/0x10
> > [   20.540456]  kthread+0xdd/0x100
> > [   20.540791]  ? __pfx_kthread+0x10/0x10
> > [   20.541190]  ret_from_fork+0x29/0x50
> > [   20.541566]  </TASK>
> > [   20.541802] ---[ end trace 0000000000000000 ]---
> > 
> > The warning is from here:
> 
> No, it comes from
> 
> static int virtio_gpu_queue_ctrl_sgs(struct virtio_gpu_device *vgdev,
> 				     struct virtio_gpu_vbuffer *vbuf,
> 				     struct virtio_gpu_fence *fence,
> 				     int elemcnt,
> 				     struct scatterlist **sgs,
> 				     int outcnt,
> 				     int incnt)
> > 
> > /* For drm_panic */
> > static int virtio_gpu_panic_queue_ctrl_sgs(struct virtio_gpu_device *vgdev,
> >                                             struct virtio_gpu_vbuffer *vbuf,
> >                                             int elemcnt,
> >                                             struct scatterlist **sgs,
> >                                             int outcnt,
> >                                             int incnt)
> > {
> >          struct virtqueue *vq = vgdev->ctrlq.vq;
> >          int ret;
> > 
> >          if (vgdev->has_indirect)
> >                  elemcnt = 1;
> > 
> >          if (vq->num_free < elemcnt)
> >                  return -ENOMEM;
> > 
> >          ret = virtqueue_add_sgs(vq, sgs, outcnt, incnt, vbuf, GFP_ATOMIC);
> >          WARN_ON(ret);
> > 
> >          vbuf->seqno = ++vgdev->ctrlq.seqno;
> >          trace_virtio_gpu_cmd_queue(vq, virtio_gpu_vbuf_ctrl_hdr(vbuf), vbuf->seqno);
> > 
> >          atomic_inc(&vgdev->pending_commands);
> > 
> >          return 0;
> > }
> > 
> > 
> > Add an option for drivers to bypass the common break+reset handling.
> > As DRM is careful to flush/synchronize outstanding buffers, it looks like
> > GPU can just have a NOP there.
> 
> So it looks like the shutdown is called in the middle of console drawing, so
> either wait for it to finish, or let drm handle the shutdown, like your
> patch does.
> 
> > 
> > Fixes: 8bd2fa086a04 ("virtio: break and reset virtio devices on device_shutdown()")
> > Cc: Eric Auger <eauger@redhat.com>
> > Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> > ---
> > 
> > Can someone who knows more about DRM and shutdown please tell me if this
> > is a good idea?  Posting for testing and early feedback, completely
> > untested.
> > 
> > 
> > 
> >   drivers/gpu/drm/virtio/virtgpu_drv.c | 9 +++++++++
> >   drivers/virtio/virtio.c              | 6 ++++++
> >   include/linux/virtio.h               | 3 +++
> >   3 files changed, 18 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/virtio/virtgpu_drv.c b/drivers/gpu/drm/virtio/virtgpu_drv.c
> > index 2d88e390feb4..210464146a9c 100644
> > --- a/drivers/gpu/drm/virtio/virtgpu_drv.c
> > +++ b/drivers/gpu/drm/virtio/virtgpu_drv.c
> > @@ -128,6 +128,14 @@ static void virtio_gpu_remove(struct virtio_device *vdev)
> >   	drm_dev_put(dev);
> >   }
> > +static void virtio_gpu_shutdown(struct virtio_device *vdev)
> > +{
> > +	/*
> > +	 * GPU is used by drm panic after shutdown.
> 
> Hopefully, there are no panic on shutdown.



OK looks like you agree with the patch, but the comments and the
commit log need to be fixed up?


> > +	 * Do nothing here, opt out of device reset.
> > +	 */
> > +}
> > +
> >   static void virtio_gpu_config_changed(struct virtio_device *vdev)
> >   {
> >   	struct drm_device *dev = vdev->priv;
> > @@ -162,6 +170,7 @@ static struct virtio_driver virtio_gpu_driver = {
> >   	.id_table = id_table,
> >   	.probe = virtio_gpu_probe,
> >   	.remove = virtio_gpu_remove,
> > +	.shutdown = virtio_gpu_shutdown,
> >   	.config_changed = virtio_gpu_config_changed
> >   };
> > diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c
> > index 150753c3b578..95d5d7993e5b 100644
> > --- a/drivers/virtio/virtio.c
> > +++ b/drivers/virtio/virtio.c
> > @@ -407,6 +407,12 @@ static void virtio_dev_shutdown(struct device *_d)
> >   	if (!drv)
> >   		return;
> > +	/* If the driver has its own shutdown method, use that. */
> > +	if (drv->shutdown) {
> > +		drv->shutdown(dev);
> > +		return;
> > +	}
> > +
> >   	/*
> >   	 * Some devices get wedged if you kick them after they are
> >   	 * reset. Mark all vqs as broken to make sure we don't.
> > diff --git a/include/linux/virtio.h b/include/linux/virtio.h
> > index 4d16c13d0df5..64cb4b04be7a 100644
> > --- a/include/linux/virtio.h
> > +++ b/include/linux/virtio.h
> > @@ -220,6 +220,8 @@ size_t virtio_max_dma_size(const struct virtio_device *vdev);
> >    *    occurs.
> >    * @reset_done: optional function to call after transport specific reset
> >    *    operation has finished.
> > + * @shutdown: synchronize with the device on shutdown. If provided, replaces
> > + *    the virtio core implementation.
> >    */
> >   struct virtio_driver {
> >   	struct device_driver driver;
> > @@ -237,6 +239,7 @@ struct virtio_driver {
> >   	int (*restore)(struct virtio_device *dev);
> >   	int (*reset_prepare)(struct virtio_device *dev);
> >   	int (*reset_done)(struct virtio_device *dev);
> > +	void (*shutdown)(struct virtio_device *dev);
> >   };
> >   #define drv_to_virtio(__drv)	container_of_const(__drv, struct virtio_driver, driver)
> 
> Best regards,
> 
> -- 
> 
> Jocelyn