Re: [Xen-devel] AMD VMMCALL and VM86 mode

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 09/12/16 19:55, Boris Ostrovsky wrote:
> On 12/09/2016 02:01 PM, Andrew Cooper wrote:
>> Hello,
>>
>> While working on XSA-192, I found a curious thing.  On AMD hardware, the
>> VMMCALL instruction appears to behave like a nop if executed in VM86
>> mode.  All other processor modes work fine.
>>
>> The documentation suggests it should be valid in any situation, but I
>> never get a #VMEXIT from it. 
> And I assume GENERAL2_INTERCEPT_VMMCALL is set (which is what we have in
> Xen by default)?

Yes, because I have already used hypercalls to get text to the console
before entering vm86 mode.

> What happens if you don't set it?

Let me do some hacking and see.

~Andrew

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