linux-kernel - Re: [PATCH] powerpc/xive: store server for masked interrupt in kvmppc_xive_set

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Date:   Tue, 5 Dec 2017 14:05:12 +1100
From:   Paul Mackerras <paulus@...abs.org>
To:     Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc:     Laurent Vivier <lvivier@...hat.com>, linux-kernel@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, kvm-ppc@...r.kernel.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Thomas Huth <thuth@...hat.com>,
        Sam Bobroff <sbobroff@...hat.com>
Subject: Re: [PATCH] powerpc/xive: store server for masked interrupt in
 kvmppc_xive_set_xive()

On Fri, Nov 24, 2017 at 07:38:13AM +1100, Benjamin Herrenschmidt wrote:
> On Thu, 2017-11-23 at 10:06 +0100, Laurent Vivier wrote:
> > This is needed to map kvmppc_xive_set_xive() behavior
> > to kvmppc_xics_set_xive().
> > 
> > As we store the server, kvmppc_xive_get_xive() can return
> > the good value and we can also allow kvmppc_xive_int_on().
> > 
> > Signed-off-by: Laurent Vivier <lvivier@...hat.com>
> > ---
> >  arch/powerpc/kvm/book3s_xive.c | 20 ++++++++------------
> >  1 file changed, 8 insertions(+), 12 deletions(-)
> > 
> > diff --git a/arch/powerpc/kvm/book3s_xive.c b/arch/powerpc/kvm/book3s_xive.c
> > index bf457843e032..2781b8733038 100644
> > --- a/arch/powerpc/kvm/book3s_xive.c
> > +++ b/arch/powerpc/kvm/book3s_xive.c
> > @@ -584,10 +584,14 @@ int kvmppc_xive_set_xive(struct kvm *kvm, u32 irq, u32 server,
> >  	 *       we could initialize interrupts with valid default
> >  	 */
> >  
> > -	if (new_act_prio != MASKED &&
> > -	    (state->act_server != server ||
> > -	     state->act_priority != new_act_prio))
> > -		rc = xive_target_interrupt(kvm, state, server, new_act_prio);
> > +	if (state->act_server != server ||
> > +	    state->act_priority != new_act_prio) {
> > +		if (new_act_prio != MASKED)
> > +			rc = xive_target_interrupt(kvm, state, server,
> > +						   new_act_prio);
> > +		if (!rc)
> > +			state->act_server = server;
> > +	}
> 
> That leads to another problem with this code. My current implementation
> is such that is a target queue is full, it will pick another target.
> But here, we still update act_server to the passed-in server and
> not the actual target...

So does that amount to a NAK?

> >  	/*
> >  	 * Perform the final unmasking of the interrupt source
> > @@ -646,14 +650,6 @@ int kvmppc_xive_int_on(struct kvm *kvm, u32 irq)
> >  
> >  	pr_devel("int_on(irq=0x%x)\n", irq);
> >  
> > -	/*
> > -	 * Check if interrupt was not targetted
> > -	 */
> > -	if (state->act_priority == MASKED) {
> > -		pr_devel("int_on on untargetted interrupt\n");
> > -		return -EINVAL;
> > -	}
> > -
> 
> So my thinking here was that act_priority was never going to be MASKED
> except if the interrupt had never been targetted anywhere at machine
> startup time. Thus if act_priority is masked, the act_server field
> cannot be trusted.
> 
> >  	/* If saved_priority is 0xff, do nothing */
> >  	if (state->saved_priority == MASKED)
> >  		return 0;

How do you think this should be fixed?

Laurent, are you reworking the patch at the moment?

Paul.