Re: Corner cases of I/O bitmap

[Gleb Natapov <gleb@redhat.com>]

On Mon, Aug 12, 2013 at 08:35:57PM +0800, Arthur Chunqi Li wrote:
> Hi Gleb and Paolo,
> There are some corner cases when testing I/O bitmaps, and I don't know
> the exact action of HW.
> 
A little bit late but...

> 1. If we set bit of 0x4000 in bitmap and call inl(0x3FFFF) or
> inl(0x4000) in guest, what will get of exit information?
> 
Spec says;
execution of an I/O instruction causes a VM exit if any bit in the I/O
bitmaps corresponding to a port it accesses is 1. Note "any" here. The
exit will have address that instruction used, otherwise how can we be
able to emulate it properly.

> 2. What will we get when calling inl(0xFFFF) in guest with/without
> “unconditional I/O exiting” VM-execution control and “use I/O bitmaps”
> VM-execution control?
In other words are you asking what happens if you do inl(0xFFFF) on real
HW?

"The result of an attempt to address beyond the I/O address space limit of
FFFFH is implementation-specific"

> 
> I test the two cases in nested env. For the first one, I got normal
> exit if any of the port accessed is masked in bitmap. For the second,
> it will acts the same as other ports. And the SDM says "If an I/O
> operation “wraps around” the 16-bit I/O-port space (accesses ports
> FFFFH and 0000H), the I/O instruction causes a VM exit." I cannot find
> the exact reaction of this case.
What do you mean by "exact reaction"?

> 
> Do you have any ideas about these?
> 
> Arthur
> 
> -- 
> Arthur Chunqi Li
> Department of Computer Science
> School of EECS
> Peking University
> Beijing, China

--
			Gleb.