Re: [PATCH] When switching to a vm8086 task, load segments as 16-bit (v2)

[Anthony Liguori <aliguori@us.ibm.com>]

Avi Kivity wrote:
> On 08/12/2009 03:11 PM, Avi Kivity wrote:
>> On 08/11/2009 11:57 PM, Anthony Liguori wrote:
>>> According to 16.2.5 in the SDM, eflags.vm in the tss is consulted 
>>> before loading
>>> and new segments.  If eflags.vm == 1, then the segments are treated 
>>> as 16-bit
>>> segments.  The LDTR and TR are not normally available in vm86 mode 
>>> so if they
>>> happen to somehow get loaded, they need to be treated as 32-bit 
>>> segments.
>>>
>>> This fixes an invalid vmentry failure in a custom OS that was 
>>> happening after
>>> a task switch into vm8086 mode.  Since the segments were being 
>>> mistakenly
>>> treated as 32-bit, we loaded garbage state.
>>
>> I'm getting a Vista x64 installer failure on reboot with this.  One 
>> possibility is that ->get_rflags() is returning the mangled flags 
>> state (we add vm86 for real mode), which confuses the new code.
>>
>
> That's indeed the case, I'm testing a patch now.

While the code looks nicer with the second patch, the fact that 
get_rflags() does a vmcs_read() seems 7 times more than before seems 
unfortunate.

-- 
Regards,

Anthony Liguori