Re: [PATCH v6 4/4] hw: replace most qemu_bh_new calls with qemu_bh_new_guarded

[Thomas Huth]

On 05/02/2023 05.07, Alexander Bulekov wrote:
> This protects devices from bh->mmio reentrancy issues.
>
> Reviewed-by: Darren Kenny <darren.kenny@oracle.com>
> Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
> Signed-off-by: Alexander Bulekov <alxndr@bu.edu>
> ---
...
> diff --git a/hw/9pfs/xen-9p-backend.c b/hw/9pfs/xen-9p-backend.c
> index 65c4979c3c..f077c1b255 100644
> --- a/hw/9pfs/xen-9p-backend.c
> +++ b/hw/9pfs/xen-9p-backend.c
> @@ -441,7 +441,9 @@ static int xen_9pfs_connect(struct XenLegacyDevice *xendev)
>           xen_9pdev->rings[i].ring.out = xen_9pdev->rings[i].data +
>                                          XEN_FLEX_RING_SIZE(ring_order);
>   
> -        xen_9pdev->rings[i].bh = qemu_bh_new(xen_9pfs_bh, &xen_9pdev->rings[i]);
> +        xen_9pdev->rings[i].bh = qemu_bh_new_guarded(xen_9pfs_bh,
> +                                                     &xen_9pdev->rings[i],
> +                                                     
> &DEVICE(xen_9pdev)->mem_reentrancy_guard);

xen_9pdev is not derived from DeviceState, so you must not cast it with 
DEVICE().

> diff --git a/hw/ide/ahci.c b/hw/ide/ahci.c
> index 7ce001cacd..37091150cb 100644
> --- a/hw/ide/ahci.c
> +++ b/hw/ide/ahci.c
> @@ -1508,7 +1508,8 @@ static void ahci_cmd_done(const IDEDMA *dma)
>       ahci_write_fis_d2h(ad);
>   
>       if (ad->port_regs.cmd_issue && !ad->check_bh) {
> -        ad->check_bh = qemu_bh_new(ahci_check_cmd_bh, ad);
> +        ad->check_bh = qemu_bh_new_guarded(ahci_check_cmd_bh, ad,
> +                                           &DEVICE(ad)->mem_reentrancy_guard);
>           qemu_bh_schedule(ad->check_bh);
>       }
>   }

Dito - ad is not derived from DeviceState, so you cannot use DEVICE() here.

(This was causing the crash in the macOS CI job)

> diff --git a/hw/ide/core.c b/hw/ide/core.c
> index 5d1039378f..8c8d1a8ec2 100644
> --- a/hw/ide/core.c
> +++ b/hw/ide/core.c
> @@ -519,7 +519,8 @@ BlockAIOCB *ide_issue_trim(
>   
>       iocb = blk_aio_get(&trim_aiocb_info, s->blk, cb, cb_opaque);
>       iocb->s = s;
> -    iocb->bh = qemu_bh_new(ide_trim_bh_cb, iocb);
> +    iocb->bh = qemu_bh_new_guarded(ide_trim_bh_cb, iocb,
> +                                   &DEVICE(s)->mem_reentrancy_guard);

IDEState s is also not directly derived from DeviceState. Not sure, but 
maybe you can get to the device here in a similar way that is done in 
ide_identify() :

     IDEDevice *dev = s->unit ? s->bus->slave : s->bus->master;

?

> diff --git a/hw/virtio/virtio-balloon.c b/hw/virtio/virtio-balloon.c
> index 746f07c4d2..309cebacc6 100644
> --- a/hw/virtio/virtio-balloon.c
> +++ b/hw/virtio/virtio-balloon.c
> @@ -908,8 +908,9 @@ static void virtio_balloon_device_realize(DeviceState *dev, 
> Error **errp)
>           precopy_add_notifier(&s->free_page_hint_notify);
>   
>           object_ref(OBJECT(s->iothread));
> -        s->free_page_bh = aio_bh_new(iothread_get_aio_context(s->iothread),
> -                                     virtio_ballloon_get_free_page_hints, s);
> +        s->free_page_bh = 
> aio_bh_new_guarded(iothread_get_aio_context(s->iothread),
> +                                             
> virtio_ballloon_get_free_page_hints, s,
> +                                             &DEVICE(s)->mem_reentrancy_guard);

You could use "dev" instead of "s" here to get rid of the DEVICE() cast.

The remaining changes look fine to me.

 Thomas