linux-kernel - Re: [Xen-devel] [PATCH] xen/events: fix unmask

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Message-ID: <20120709141915.GB9580@phenom.dumpdata.com>
Date:	Mon, 9 Jul 2012 10:19:15 -0400
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Stefano Stabellini <stefano.stabellini@...citrix.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>
Subject: Re: [Xen-devel] [PATCH] xen/events: fix unmask_evtchn for PV on HVM
 guests

On Fri, Jun 22, 2012 at 05:26:07PM +0100, Stefano Stabellini wrote:
> When unmask_evtchn is called, if we already have an event pending, we
> just set evtchn_pending_sel waiting for local_irq_enable to be called.
> That is because PV guests set the irq_enable pvops to

Can you point out where the PV guests do that please? Even just
including a snippet of code would be nice so that somebody
in the future has an idea of where it was/is.

> xen_irq_enable_direct that also handles pending events.
> 
> However HVM guests (and ARM guests) do not change or do not have the
> irq_enable pvop, so evtchn_unmask cannot work properly for them.

Duh!
> 
> Considering that having the pending_irq bit set when unmask_evtchn is
> called is not very common, and it is simpler to keep the

Unless you pin the guests on the vCPUS on which domain0 is not present..

> native_irq_enable implementation for HVM guests (and ARM guests), the
> best thing to do is just use the EVTCHNOP_unmask hypercall (Xen
> re-injects pending events in response).

And by re-injects you mean than the IOAPIC or (whatever it is on ARM)
is armed to show that there is a pending interrupt, right?

> 
> Signed-off-by: Stefano Stabellini <stefano.stabellini@...citrix.com>
> ---
>  drivers/xen/events.c |    7 +++++--
>  1 files changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/xen/events.c b/drivers/xen/events.c
> index eae0d0b..0132505 100644
> --- a/drivers/xen/events.c
> +++ b/drivers/xen/events.c
> @@ -372,8 +372,11 @@ static void unmask_evtchn(int port)
>  
>  	BUG_ON(!irqs_disabled());
>  
> -	/* Slow path (hypercall) if this is a non-local port. */
> -	if (unlikely(cpu != cpu_from_evtchn(port))) {
> +	/* Slow path (hypercall) if this is a non-local port or if this is
> +	 * an hvm domain and an event is pending (hvm domains don't have
> +	 * their own implementation of irq_enable). */
> +	if (unlikely((cpu != cpu_from_evtchn(port)) ||
> +			(xen_hvm_domain() && sync_test_bit(port, &s->evtchn_pending[0])))) {
>  		struct evtchn_unmask unmask = { .port = port };

We already have two seperate acks - for when there is an GMFN APIC bitmap and
when there is not. Can we also have to seperate unmask_evtchn then? And
just have the HVM and ARM just do a straightforward unmaks_evtchn while
the PV remains the same?

>  		(void)HYPERVISOR_event_channel_op(EVTCHNOP_unmask, &unmask);
>  	} else {
> 
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