Re: [Xen-devel] Emulation and active (valid) interrupts

[Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>]

On 8/13/18 3:58 PM, Jan Beulich wrote:
>>>> On 13.08.18 at 14:51, <rcojocaru@xxxxxxxxxxxxxxx> wrote:
>> So first we've got that vmx_idtv_reinject() call writing to the VMCS,
>> then we emulate a CLI, then the failed vmentry. I can't tell if the CLI
>> ran first and then an interrupt popped up, or if an interrupt had
>> already been __vmwrit()ten and then CLI caused the invalid guest state.
> 
> I'd expect it to be the latter - an external interrupt presumably
> can't be injected when EFLAGS.IF is clear. Why are we emulating
> CLI in the first place? With a pending external interrupt, shouldn't
> we just exit back to guest context without emulating anything?

In this particular case we're emulating CLI because the vm_event
response requests it.

Tamas' test marks all of the guest's pages XENMEM_access_x, and at some
point a vm_event arrives somewhere in a page where CLI is read from,
AFAICT. Doing nothing would get us into an infinite loop, and since we
don't want to mark the page rwx, we try to emulate CLI.


Thanks,
Razvan

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