RE: [Xen-devel] one question on the PCI ioport base address forhvm domain in hvmloader.c

["Jiang, Yunhong" <yunhong.jiang@xxxxxxxxx>]

Yes, the guest OS should be allowed to remap BAR.
But I don't know are there any OS will try to remap BAR, except Vista.
And even in Vista, we can still try to disable BAR remapping through
bcdedit.
The benifit to set guest IO port address same as physical one is, if
guest didn't try to remap, then it can access IO port directly without
cause VMExit. That may help performance. Although IO port is not so
important for PCI device now, but that may still be helpful on some
situation, considering USB 1.1 device.
Of course,we need still support the BAR remapping, what we can do is,
our guest BIOS (hvmloader in fact) will set the initial value same to
physical one.


-- Yunhong Jiang

xen-devel-bounces@xxxxxxxxxxxxxxxxxxx <> wrote:
> Why not keep the level of indirection? After all, the guest OS should
be
> allowed to remap any BAR and we should support that.
> 
> -- Keir
> 
> On 7/1/08 11:47, "Jiang, Yunhong" <yunhong.jiang@xxxxxxxxx> wrote:
> 
>> I'm considering to make guest IO port address same as physical one
for
>> passthrough hvm domain. However,  in hvmloader.c's pci_setup(), the
>> io_base is hardcoded as 0xc000, are there any special reason for this
>> value? (I checked and seems it comes from original qemu's code)
>> 
>> Can anyone give me some hints on it?
>> 
>> Thanks
>> -- Yunhong Jiang
>> 
>> _______________________________________________
>> Xen-devel mailing list
>> Xen-devel@xxxxxxxxxxxxxxxxxxx
>> http://lists.xensource.com/xen-devel
> 
> 
> 
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