Re: [PATCH] KVM: arm64: ITS: avoid re-mapping LPIs

[Christoffer Dall <christoffer.dall@linaro.org>]

On Tue, Aug 16, 2016 at 05:51:06PM +0100, Andre Przywara wrote:
> When a guest wants to map a device-ID/event-ID combination that is
> already mapped, we may end up in a situation where an LPI is never
> "put", thus never being freed.
> Since the GICv3 spec says that mapping an already mapped LPI is
> UNPREDICTABLE, lets just bail out early in this situation to avoid
> any potential leaks.
> 
> Signed-off-by: Andre Przywara <andre.przywara@arm.com>
> ---
>  virt/kvm/arm/vgic/vgic-its.c | 27 +++++++++++++--------------
>  1 file changed, 13 insertions(+), 14 deletions(-)
> 
> diff --git a/virt/kvm/arm/vgic/vgic-its.c b/virt/kvm/arm/vgic/vgic-its.c
> index 9533080..4660a7d 100644
> --- a/virt/kvm/arm/vgic/vgic-its.c
> +++ b/virt/kvm/arm/vgic/vgic-its.c
> @@ -731,7 +731,7 @@ static int vgic_its_cmd_handle_mapi(struct kvm *kvm, struct vgic_its *its,
>  	u32 device_id = its_cmd_get_deviceid(its_cmd);
>  	u32 event_id = its_cmd_get_id(its_cmd);
>  	u32 coll_id = its_cmd_get_collection(its_cmd);
> -	struct its_itte *itte, *new_itte = NULL;
> +	struct its_itte *itte;
>  	struct its_device *device;
>  	struct its_collection *collection, *new_coll = NULL;
>  	int lpi_nr;
> @@ -749,6 +749,10 @@ static int vgic_its_cmd_handle_mapi(struct kvm *kvm, struct vgic_its *its,
>  	    lpi_nr >= max_lpis_propbaser(kvm->arch.vgic.propbaser))
>  		return E_ITS_MAPTI_PHYSICALID_OOR;
>  
> +	/* If there is an existing mapping, behavior is UNPREDICTABLE. */
> +	if (find_itte(its, device_id, event_id))
> +		return 0;
> +

By the way, this made me think how these errors are handled, and unless
I'm mistaken, the return value from vgic_its_handle_command() is simply
discarded, so even when we return things like -ENOMEM, this is just
ignored?  Is this really the intention?

Thanks,
-Christoffer