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Re: [Qemu-devel] usb: usb tablet freeze when save/restore guest os

From: Gonglei (Arei)
Subject: Re: [Qemu-devel] usb: usb tablet freeze when save/restore guest os
Date: Wed, 14 May 2014 01:47:30 +0000

> -----Original Message-----
> From: Gerd Hoffmann [mailto:address@hidden
> Sent: Tuesday, May 13, 2014 9:27 PM
> To: Gonglei (Arei)
> Cc: address@hidden; Huangweidong (C); Michael S. Tsirkin
> Subject: Re: usb: usb tablet freeze when save/restore guest os
>   Hi,
> > In the situation of save/restore guest os, when the guest os is saving
> > memory iteratively, meanwhile the usb tablet work normally (by vnc). When
> qemu
> > has set the UHCI_PORT_RD bit to 1, and post a interrupt to guest os, but
> > guest os has hibernated this moment, so the interrupt cannot be handled
> > in time. So, the UHCI_PORT_RD bit will not be cleared by
> uhci_finish_suspend().
> > When we restore the guest os, and the usb tablet event happen again, but
> > because of UHCI_PORT_RD bit being set to 1, qemu consider the guest os is
> > handling the interrupt of resuming UHCI, so will not post another interrupt.
> Another interrupt should not be needed.  If we don't deliver the
> interrupt before suspend, we must deliver it after resume. 
The fact is that an interrupt has been delivered during suspend, and guest os 
response it.

>It must not get lost, loosing interrupts can cause all sorts of problems.
Yes. Strongly agreed.

> There was a kernel bug recently causing lost interrupts on migration,
> maybe this is the same (rh bug 1036478)?  Paolo?  Is the fix upstream?
> Which kernel has it?
Oh? Sounds good.

Cc'ing Paolo for attention. Thanks.

Best regards,

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