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Re: [Xen-devel] qemu(-dm): aborting on wrong mmio size?

>>> On 31.01.12 at 12:04, Laszlo Ersek <lersek@xxxxxxxxxx> wrote:
> On 01/31/12 11:36, Jan Beulich wrote:
>>>>> On 31.01.12 at 10:34, Laszlo Ersek<lersek@xxxxxxxxxx>  wrote:
>>> Is it justified to kill the emulator when this happens (eg. memory
>>> mapped IO with 64-bit operand)?
>> The AMD manual specifies that REX.W is ignored; the Intel manual
>> doesn't mention REX at all here. However, if a decoder incorrectly
>> decodes the guest instruction, that's a bug there. So imo qemu
>> validly treats this condition as fatal.
>  From the Itanium(R) SDM rev 2.3,
> I/O Port Addressing Restrictions
>      For the 64MB physical I/O port block the following operations are
>      undefined and may result in unpredictable processor operation;
>      references larger than 4-bytes, [...]
> It seems that not only a decoding failure can trigger this.

Oh, yes, I forgot that port I/O goes via MMIO on ia64. So yes, for
that case your observation is correct, though killing qemu-dm in
that case still seems to fall well under "undefined behavior". But
improving the situation wouldn't be bad then.


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