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Re: [Xen-devel] [PATCH] evtchn: make support for different ABIs tunable


  • To: Eslam Elnikety <elnikety@xxxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxxx>
  • From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
  • Date: Wed, 7 Aug 2019 12:40:56 +0100
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  • Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>, George Dunlap <George.Dunlap@xxxxxxxxxxxxx>, Tim Deegan <tim@xxxxxxx>, Ian Jackson <ian.jackson@xxxxxxxxxxxxx>, Julien Grall <julien.grall@xxxxxxx>, Jan Beulich <jbeulich@xxxxxxxx>, Anthony PERARD <anthony.perard@xxxxxxxxxx>, David Woodhouse <dwmw@xxxxxxxxxxxx>
  • Delivery-date: Wed, 07 Aug 2019 11:41:06 +0000
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  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
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On 07/08/2019 12:20, Eslam Elnikety wrote:
> Adding support for FIFO event channel ABI was first introduced in Xen 4.4
> (see 88910061ec6). Make this support tunable, since the choice of which
> event channel ABI has implications for hibernation. Consider resuming a
> pre Xen 4.4 hibernated Linux guest. The guest boot kernel defaults to FIFO
> ABI, whereas the resume kernel assumes 2L. This, in turn, results in Xen
> and the resumed kernel talking past each other (due to different protocols
> FIFO vs 2L).

I'm afraid I don't follow.

We have a Linux kernel which knows about FIFO, which was first booted on
Xen < 4.4, so configured 2L mode.

It is then suspended, and resumed on a newer Xen >= 4.4.  The guest now
has a choice between 2L mode, and FIFO mode.

What is the problem?

When resuming, the guest in question should continue to use 2L mode,
because that is what it was using previously.

~Andrew

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