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From: Avi Kivity <avi@redhat.com>
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Subject: Re: [Qemu-devel] Re: QEMU-KVM and video performance
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To: Gerhard Wiesinger <lists@wiesinger.com>
Cc: qemu-devel@nongnu.org, kvm@vger.kernel.org

On 04/21/2010 09:14 PM, Gerhard Wiesinger wrote:
>
> Can you explain which code files/functions of KVM is involved in 
> handling VGA memory window and page switching through the port write 
> to the VGA window register (or is that part handled through QEMU), so 
> a little bit architecture explaination would be nice?

qemu hw/vga.c and hw/cirrus_vga.c.  Boring functions like 
vbe_ioport_write_data() and vga_ioport_write().

>
> BTW: In which KVM code parts is decided where "direct code" or an 
> "emulated device code" is used?
>

Same place.  Look for calls to cpu_register_physical_memory().  If the 
last argument was obtained by a call to cpu_register_io_memory(), then 
all writes trap.  Otherwise, it was obtained by qemu_ram_alloc() and 
writes will not trap (except the first write to a page in a 30ms window, 
used to note that the page is dirty and needs redrawing).


-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.