Re: [Xen-devel] [PATCH] x86/emulate: Check current->arch.vm_event in hvmemul_virtual_to_linear()

[Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>]

On 04/07/16 20:54, Razvan Cojocaru wrote:
> On 04/07/16 20:27, Jan Beulich wrote:
>>>>> On 07.04.16 at 10:39, <rcojocaru@xxxxxxxxxxxxxxx> wrote:
>>> Theoretically it is possible for mem_access_emulate_each_rep to be
>>> true even when current->arch.vm_event == NULL, so add an extra
>>> check to hvmemul_virtual_to_linear().
>>
>> Mind saying what those theoretical conditions are when this might
>> happen?
> 
> This could happen if someone were to call xc_monitor_emulate_each_rep(),
> but not xc_monitor_enable() (when current->arch.vm_event gets
> allocated), or after someone called both, but afterwards called
> xc_monitor_disable() (when current->arch.vm_event gets freed).

Actually, I need to correct myself here: only the first case applies. I
was looking at older Xen source code, but there's a
"d->arch.mem_access_emulate_each_rep = 0;" statement in
vm_event_cleanup_domain() now, so calling xc_monitor_disable() would not
cause a problem.


Thanks,
Razvan

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