linux-kernel - Re: [Xen-devel] [PATCH] xen/events: remove event handling recursion detection

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Date:   Mon, 4 Nov 2019 15:35:09 +0100
From:   Jan Beulich <jbeulich@...e.com>
To:     Juergen Gross <jgross@...e.com>
Cc:     xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org,
        Stefano Stabellini <sstabellini@...nel.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>
Subject: Re: [Xen-devel] [PATCH] xen/events: remove event handling recursion
 detection

On 04.11.2019 14:58, Juergen Gross wrote:
> __xen_evtchn_do_upcall() contains guards against being called
> recursively. This mechanism was introduced in the early pvops times
> (kernel 2.6.26) when there were still Xen versions around not honoring
> disabled interrupts for sending events to pv guests.
> 
> This was changed in Xen 3.0, which is much older than any Xen version
> supported by the kernel, so the recursion detection can be removed.

Would you mind pointing out which exact change(s) this was(were)?
It had always been my understanding that the recursion detection
was mainly to guard against drivers re-enabling interrupts
transiently in their handlers (which in turn may no longer be an
issue in modern Linux kernels).

Jan