How to switch VGA passthrough live

[于佳耕 <yujiageng734@gmail.com>]

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Hi,



I want to switch video card live between two HVMs. My simplest idea is that
when the HVM has the permission to access passthrough video card, and
another HVM will be paused. If switch from A to B, execute commands :



xm pause A ;

xm pci-detach A  00:00:02.0 ;

xm pci-attach B 00:00:02.0 ;

xm unpause B.



I have a try, but failed. The pseudo-code is as below. Can you give me some
ideas? Any suggestions will be thankful.



Execute “xm pci-detach Domain 00:00:02.0”:

1.       Raise sci interrupt to unplug the device. If OSPM doesn’t handle
the unplug process, and then invoke acpi_php_writeb to power off the device.

2.       Modify power_off_php_devfn function:

int power_off_php_devfn(int php_devfn)

{

                    If(php_devfn == 0x10)  // Intel integrated graphics

                    {

                             p = & dpci_infos.php_devs[php_devfn];



       // save the two-tuples : (php_dev, domid)

       save_php_device_by_domid(p,domid);



       // hide the device from bus and dpci_infos

                             pci_hide_device(& p->pt_dev->dev);

                             memset(p,0x00,sizeof(struct php_dev));



                             return 0;

                    }

    return unregister_real_device(php_devfn);

}



Execute “xm pci-attach Domain 00:00:02.0”:

1.       Modify power_on_php_devfn function:

int power_off_php_devfn(int devfn)

{

           ….

           while(devfn == 0x10) // Intel integrated graphics

           {

                    if( ! get_php_device_by_domid(p,domid) ) // get saved
php_dev struct

                             break;                                     //
cannot get , create new one



                    //restore the php device to bus and dpci_infos

                    restore_php_device(p,devfn);         // restore
dpci_infos.php_devs[devfn]

                    dpci_infos->e_bus->devices[devfn] = p-> pt_dev->dev;



                    return 0;

           }



           if (!dpci_infos.pci_access)

           {…}

           pt_dev = register_real_device(..);

  return 0;

}



This plan hides the VGA device from HVM and never destroys it. Both mmio and
pio maps are reserved. When finishing “xm unpause B”, it seems working well
observed by Dom0 serial port login. But the screen is black and cannot
receive any signal. I am confusing. Video BIOS should be reloaded? Or need
raise some interrupt to flush screen?





Thanks & Regards,
Yujiageng

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