Subject: Re: [PATCH] KVM: PPC: Book3S: fix XIVE migration of pending interrupts

From: Laurent Vivier <[email-masked]>
Date: Tue, 12 Dec 2017 14:15:20 +0100

On 12/12/2017 13:02, Cédric Le Goater wrote:
> When restoring a pending interrupt, we are setting the Q bit to force
> a retrigger in xive_finish_unmask(). But we also need to force an EOI
> in this case to reach the same initial state : P=1, Q=0.
> 
> This can be done by not setting 'old_p' for pending interrupts which
> will inform xive_finish_unmask() that an EOI needs to be sent.
> 
> Suggested-by: Benjamin Herrenschmidt <[email-masked]>
> Signed-off-by: Cédric Le Goater <[email-masked]>
> ---
> 
>  Tested with a guest running iozone.
> 
>  arch/powerpc/kvm/book3s_xive.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/powerpc/kvm/book3s_xive.c b/arch/powerpc/kvm/book3s_xive.c
> index bf457843e032..b5e6d227a034 100644
> --- a/arch/powerpc/kvm/book3s_xive.c
> +++ b/arch/powerpc/kvm/book3s_xive.c
> @@ -1558,7 +1558,7 @@ static int xive_set_source(struct kvmppc_xive *xive, long irq, u64 addr)
>  
>  	/*
>  	 * Restore P and Q. If the interrupt was pending, we
> -	 * force both P and Q, which will trigger a resend.
> +	 * force Q and !P, which will trigger a resend.
>  	 *
>  	 * That means that a guest that had both an interrupt
>  	 * pending (queued) and Q set will restore with only
> @@ -1566,7 +1566,7 @@ static int xive_set_source(struct kvmppc_xive *xive, long irq, u64 addr)
>  	 * is perfectly fine as coalescing interrupts that haven't
>  	 * been presented yet is always allowed.
>  	 */
> -	if (val & KVM_XICS_PRESENTED || val & KVM_XICS_PENDING)
> +	if (val & KVM_XICS_PRESENTED && !(val & KVM_XICS_PENDING))
>  		state->old_p = true;
>  	if (val & KVM_XICS_QUEUED || val & KVM_XICS_PENDING)
>  		state->old_q = true;
> 

Reviewed-by: Laurent Vivier <[email-masked]>
Tested-by: Laurent Vivier <[email-masked]>