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HOW, WHEN guest access host pci configuration info? #4

Open mountainlion0523 opened 9 years ago

mountainlion0523 commented 9 years ago

in vga-vgt.c, "finish_post( )" gets host device info and renew QEMU's VGA PCI configuration information such as vendor id and device id.

But i accidentally erased finish_post function and execute KVMGT-qemu, so it seems there is no way that guest gets host's VGA configuration information, but surprisingly, guest catches host device and boot in VGA pass-through mode.

how is it possible? i wonder how guest get host VGA information and chage graphics mode from legacy VGA mode to pass through mode

l1viathan commented 9 years ago

Yes, I agree. I don't understand how it's possible.

yumbrad commented 8 years ago

Likewise, I was trying to understand the overriding of the i440x config write, so I ran qemu with a breakpoint set on finish_post (I didn't erase it). The breakpoint never hit, though everything ran appropriately. This is within the 2016Q1 example ISO and building Qemu from the 2016Q1 branch, then executing on the linux VM that comes with the ISO (/root/ubuntu-guest.qcow2) ... It seems the SeaBIOS never does the special write of 0xB105DEAD to the vendor_id area, and it works fine anyway? Note this was using KVM, not Xen.

l1viathan commented 8 years ago

It should be only hit by Windows guest, and I'm not quite sure if Windows still need this bit nowadays :)

Thanks, Jike

On 07/13/2016 01:31 AM, yumbrad wrote:

Likewise, I was trying to understand the overriding of the i440x config write, so I ran qemu with a breakpoint set on finish_post (I didn't erase it). The breakpoint never hit, though everything ran appropriately. This is within the 2016Q1 example ISO and building Qemu from the 2016Q1 branch, then executing on the linux VM that comes with the ISO (/root/ubuntu-guest.qcow2) ... It seems the SeaBIOS never does the special write of 0xB105DEAD to the vendor_id area, and it works fine anyway?

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