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

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Date:   Fri, 24 Nov 2017 07:38:13 +1100
From:   Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:     Laurent Vivier <lvivier@...hat.com>, linux-kernel@...r.kernel.org
Cc:     linuxppc-dev@...ts.ozlabs.org, kvm-ppc@...r.kernel.org,
        Paul Mackerras <paulus@...abs.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 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...

>  	/*
>  	 * 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;