Re: [PATCH 2/2] KVM: PPC: Book3S HV: Exit on H_DOORBELL only if HOST_IPI is set

[David Gibson <david@gibson.dropbear.id.au>]

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On Thu, Sep 03, 2015 at 03:21:23PM +1000, Paul Mackerras wrote:
> From: "Gautham R. Shenoy" <ego@linux.vnet.ibm.com>
> 
> The code that handles the case when we receive a H_DOORBELL interrupt
> has a comment which says "Hypervisor doorbell - exit only if host IPI
> flag set".  However, the current code does not actually check if the
> host IPI flag is set.  This is due to a comparison instruction that
> got missed.
> 
> As a result, the current code performs the exit to host only
> if some sibling thread or a sibling sub-core is exiting to the
> host.  This implies that, an IPI sent to a sibling core in
> (subcores-per-core != 1) mode will be missed by the host unless the
> sibling core is on the exit path to the host.
> 
> This patch adds the missing comparison operation which will ensure
> that when HOST_IPI flag is set, we unconditionally exit to the host.
> 
> Fixes: 66feed61cdf6
> Cc: stable@vger.kernel.org # v4.1+
> Signed-off-by: Gautham R. Shenoy <ego@linux.vnet.ibm.com>
> Signed-off-by: Paul Mackerras <paulus@samba.org>

Reviewed-by: David Gibson <david@gibson.dropbear.id.au>

> ---
>  arch/powerpc/kvm/book3s_hv_rmhandlers.S | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/arch/powerpc/kvm/book3s_hv_rmhandlers.S b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
> index b07f045..2273dca 100644
> --- a/arch/powerpc/kvm/book3s_hv_rmhandlers.S
> +++ b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
> @@ -1213,6 +1213,7 @@ END_FTR_SECTION_IFSET(CPU_FTR_HAS_PPR)
>  	cmpwi	r12, BOOK3S_INTERRUPT_H_DOORBELL
>  	bne	3f
>  	lbz	r0, HSTATE_HOST_IPI(r13)
> +	cmpwi	r0, 0
>  	beq	4f
>  	b	guest_exit_cont
>  3:

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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