Re: [PATCH v5 05/10] KVM: arm/arm64: vgic-its: Save the collection table before device tables

Christoffer Dall
2017-10-25T09:59:57Z

On Mon, Oct 23, 2017 at 04:08:24PM +0200, Eric Auger wrote:
> Currently the ITS caches are not emptied on reset.
>
> After a reset, in case we attempt to save the state before
> the bound devices have registered their MSIs and after the
> 1st level table has been allocated by the ITS driver
> (device BASER is valid), the first level entries are still
> invalid. If the device cache is not empty (devices registered
> before the reset), vgic_its_save_device_tables fails.
>
> This failure has no consequence as those devices do not
> deserve to be saved: they correspond to the state before
> the reset.
>
> However the ITS driver already sent MAPC for collections
> and those need to be saved. With the current code, they
> will not and the restored guest will not work properly.
>
> So this patch saves collection tables before device tables.
>
> Signed-off-by: Eric Auger <eric.auger@redhat.com>
>
> ---
>
> candidate to be CC'ed stable
> ---
> virt/kvm/arm/vgic/vgic-its.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/virt/kvm/arm/vgic/vgic-its.c b/virt/kvm/arm/vgic/vgic-its.c
> index b6650c2..8472417 100644
> --- a/virt/kvm/arm/vgic/vgic-its.c
> +++ b/virt/kvm/arm/vgic/vgic-its.c
> @@ -2324,11 +2324,11 @@ static int vgic_its_save_tables_v0(struct vgic_its *its)
> return -EBUSY;
> }
>
> - ret = vgic_its_save_device_tables(its);
> + ret = vgic_its_save_collection_table(its);
> if (ret)
> goto out;
>
> - ret = vgic_its_save_collection_table(its);
> + ret = vgic_its_save_device_tables(its);
>

I don't understand this. It seems to indicate an ordering of device
tables vs. collection tables. What is that?

I thought the point was that you'd want to save the valid table, and not
save the other one.

So, aren't we looking for something like this:

ret = vgic_its_save_device_tables(its);
if (ret < 0)
goto out;

ret = vgic_its_save_collection_table(its);

Thanks,
-Christoffer