Re: [Xen-devel] The use of evtchn_upcall_mask

[Yaogun Wen <techno.geek.0x01@xxxxxxxxx>]

On 2012/9/21 at pm 9:24 Ian Campbell wrote:
> It is read from assembly code (entry.S) accessed via
> VCPUINFO_upcall_mask which is defined using the asm-offsets.c mechanism.
>
> local_event_delivery_is_enabled seems to be redundant these days.
Thank you for your guidance. :)
But I still have some questions, please keep reading.

On 2012/9/21 at pm 9:29 Jan Beulich wrote:
> Setting an event channel pending isn't tied to the channel being
> unmasked - in particular, for polled event channels, one would
> keep them masked permanently, yet still expect events to be
> signaled. The mask really controls whether an upcall is actually
> permitted (just like EFLAGS.IF controls whether interrupts can
> be injected).
This explanation helps me to understand the meaning of VCPUINFO_upcall_mask.
I don't know x86 assembly language, but according to your explanation,
it seems that guest which only have masked channel will still receive
the events.
But from the comment of vcpu_info struct, it says "The mask
(evtchn_upcall_mask) is read before making an event upcall to the
guest".
So, which one is correct?


-- 
Best regards,

Yao-Jing Wen

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