Re: [PATCH v5 10/10] KVM: arm/arm64: vgic-its: Implement KVM_DEV_ARM_ITS_CTRL_RESET

[Marc Zyngier]

On Mon, Oct 23 2017 at  4:08:29 pm BST, Eric Auger <eric.auger@xxxxxxxxxx> wrote:
> On reset we clear the valid bits of GITS_CBASER and GITS_BASER<n>.
> We also clear command queue registers and free the cache (device,
> collection, and lpi lists).
>
> Signed-off-by: Eric Auger <eric.auger@xxxxxxxxxx>
> Reviewed-by: Christoffer Dall <christoffer.dall@xxxxxxxxxx>
>
> ---
>
> v2 -> v3:
> - added Christoffer's R-b
> ---
>  arch/arm/include/uapi/asm/kvm.h   |  1 +
>  arch/arm64/include/uapi/asm/kvm.h |  1 +
>  virt/kvm/arm/vgic/vgic-its.c      | 18 ++++++++++++++++++
>  3 files changed, 20 insertions(+)
>
> diff --git a/arch/arm/include/uapi/asm/kvm.h b/arch/arm/include/uapi/asm/kvm.h
> index 5db2d4c..7ef0c06 100644
> --- a/arch/arm/include/uapi/asm/kvm.h
> +++ b/arch/arm/include/uapi/asm/kvm.h
> @@ -215,6 +215,7 @@ struct kvm_arch_memory_slot {
>  #define   KVM_DEV_ARM_ITS_SAVE_TABLES		1
>  #define   KVM_DEV_ARM_ITS_RESTORE_TABLES	2
>  #define   KVM_DEV_ARM_VGIC_SAVE_PENDING_TABLES	3
> +#define   KVM_DEV_ARM_ITS_CTRL_RESET		4
>  
>  /* KVM_IRQ_LINE irq field index values */
>  #define KVM_ARM_IRQ_TYPE_SHIFT		24
> diff --git a/arch/arm64/include/uapi/asm/kvm.h b/arch/arm64/include/uapi/asm/kvm.h
> index 9f3ca24..b5306ce 100644
> --- a/arch/arm64/include/uapi/asm/kvm.h
> +++ b/arch/arm64/include/uapi/asm/kvm.h
> @@ -227,6 +227,7 @@ struct kvm_arch_memory_slot {
>  #define   KVM_DEV_ARM_ITS_SAVE_TABLES           1
>  #define   KVM_DEV_ARM_ITS_RESTORE_TABLES        2
>  #define   KVM_DEV_ARM_VGIC_SAVE_PENDING_TABLES	3
> +#define   KVM_DEV_ARM_ITS_CTRL_RESET		4
>  
>  /* Device Control API on vcpu fd */
>  #define KVM_ARM_VCPU_PMU_V3_CTRL	0
> diff --git a/virt/kvm/arm/vgic/vgic-its.c b/virt/kvm/arm/vgic/vgic-its.c
> index bdfceb4..64b6b04 100644
> --- a/virt/kvm/arm/vgic/vgic-its.c
> +++ b/virt/kvm/arm/vgic/vgic-its.c
> @@ -2395,6 +2395,19 @@ static int vgic_its_commit_v0(struct vgic_its *its)
>  	return 0;
>  }
>  
> +static void vgic_its_reset(struct kvm *kvm, struct vgic_its *its)
> +{
> +	/* We need to keep the ABI specific field values */
> +	its->baser_coll_table &= ~GITS_BASER_VALID;
> +	its->baser_device_table &= ~GITS_BASER_VALID;
> +	its->cbaser = 0;
> +	its->creadr = 0;
> +	its->cwriter = 0;
> +	its->enabled = 0;
> +	vgic_its_free_device_list(kvm, its);
> +	vgic_its_free_collection_list(kvm, its);

I sense a problem here. There is no locking when resetting the fields,
and there is no guarantee that no vcpus are running at this stage (we
rely on a well behaved userspace).

How do we ensure this? We should move the checks we have in the
save/restore functions to a common location vgic_its_set_attr and
protect all the call sites.

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny.