On 04/22/2010 08:37 AM, Gerhard Wiesinger wrote:
On Wed, 21 Apr 2010, Avi Kivity wrote:
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().
Yes, I was already in that code part and that are very simple
functions as already explained and are therefore in QEMU only very
fast. But I ment: How is the calling path from KVM guest OS to
hw/vga.c for memory and I/O accesses, and which parts are done in
hardware directly (to understand the speed gap and maybe to find a
solution)?
The speed gap is mostly due to hardware constraints (it takes ~2000
cycles for an exit from guest mode, plus we need to switch a few msrs to
get to userspace).
See vmx_vcpu_run(), the vmresume instruction is where an exit starts.
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).
Ok, that finally ends in:
cpu_register_physical_memory_offset()
...
// 0.12.3
if (kvm_enabled())
kvm_set_phys_mem(start_addr, size, phys_offset);
// KVM
cpu_notify_set_memory(start_addr, size, phys_offset);
...
I/O is always done through:
cpu_register_io_memory => cpu_register_io_memory_fixed
cpu_register_io_memory_fixed()
...
No call to KVM?
kvm_set_phys_mem() is a call to kvm.
...
Where is the trap from KVM to QEMU?
See kvm_cpu_exec().
--
error compiling committee.c: too many arguments to function
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