linux-kernel - Re: [PATCH] xen: Revert commits da72ff5bfcb0 and 72a9b186292d

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Date:   Tue, 25 Apr 2017 10:58:31 +0200
From:   Juergen Gross <jgross@...e.com>
To:     Boris Ostrovsky <boris.ostrovsky@...cle.com>
Cc:     karahmed@...zon.de, sstabellini@...nel.org,
        xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] xen: Revert commits da72ff5bfcb0 and 72a9b186292d

On 24/04/17 21:04, Boris Ostrovsky wrote:
> Recent discussion (http://marc.info/?l=xen-devel&m=149192184523741)
> established that commit 72a9b186292d ("xen: Remove event channel
> notification through Xen PCI platform device") (and thus commit
> da72ff5bfcb0 ("partially revert "xen: Remove event channel
> notification through Xen PCI platform device"")) are unnecessary and,
> in fact, prevent HVM guests from booting on Xen releases prior to 4.0
> 
> Therefore we revert both of those commits.
> 
> The summary of that discussion is below:
> 
>   Here is the brief summary of the current situation:
> 
>   Before the offending commit (72a9b186292):
> 
>   1) INTx does not work because of the reset_watches path.
>   2) The reset_watches path is only taken if you have Xen > 4.0
>   3) The Linux Kernel by default will use vector inject if the hypervisor
>      support. So even INTx does not work no body running the kernel with
>      Xen > 4.0 would notice. Unless he explicitly disabled this feature
>      either in the kernel or in Xen (and this can only be disabled by
>      modifying the code, not user-supported way to do it).
> 
>   After the offending commit (+ partial revert):
> 
>   1) INTx is no longer support for HVM (only for PV guests).
>   2) Any HVM guest The kernel will not boot on Xen < 4.0 which does
>      not have vector injection support. Since the only other mode
>      supported is INTx which.
> 
>   So based on this summary, I think before commit (72a9b186292) we were
>   in much better position from a user point of view.
> 
> Signed-off-by: Boris Ostrovsky <boris.ostrovsky@...cle.com>

Reviewed-by: Juergen Gross <jgross@...e.com>


Thanks,

Juergen