Re: XSM and the idle domain

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 21/10/2020 15:34, Hongyan Xia wrote:
> The first question came up during ongoing work in LiveUpdate. After an
> LU, the next Xen needs to restore all domains. To do that, some
> hypercalls need to be issued from the idle domain context and
> apparently XSM does not like it.

There is no such thing as issuing hypercalls from the idle domain
(context or otherwise), because the idle domain does not have enough
associated guest state for anything to make the requisite
SYSCALL/INT80/VMCALL/VMMCALL invocation.

I presume from this comment that what you mean is that you're calling
the plain hypercall functions, context checks and everything, from the
idle context?

If so, this is buggy for more reasons than just XSM objecting to its
calling context, and that XSM is merely the first thing to explode. 
Therefore, I don't think modifications to XSM are applicable to solving
the problem.

(Of course, this is all speculation because there's no concrete
implementation to look at.)

~Andrew