Re: [Qemu-devel] [PATCH v2 1/3] s390x/sclp: proper support of larger send and receive masks

[Cornelia Huck <cohuck@redhat.com>]

On Thu, 22 Feb 2018 17:22:57 +0100
Claudio Imbrenda <imbrenda@linux.vnet.ibm.com> wrote:

> Until 67915de9f0383ccf4a ("s390x/event-facility: variable-length event masks")
> we only supported sclp event masks of size exactly 4 bytes, even though

s/of size/of a size of/

> the archiecture allows the guests to set up sclp event masks from 1 to

s/archiecture/architecture/

> 1021 bytes in length.
> After that patch, the behaviour was almost compliant, but some issues
> were still remaining, in particular regarding the handling of selective
> reads and migration.
> 
> When setting the sclp event mask, a mask size is also specified. Until
> now we only considered the size in order to decide which bits to save
> in the internal state. On the other hand, when a guest performs a
> selective read, it sends a mask, but it does not specify a size; the
> implied size is the size of the last mask that has been set.
> 
> Specifying bits in the mask of selective read that are not available in
> the internal mask should return an error, and bits past the end of the
> mask should obviously be ignored. This can only be achieved by keeping
> track of the lenght of the mask.
> 
> The mask length is thus now part of the internal state that needs to be
> migrated.
> 
> This patch fixes the handling of selective reads, whose size will now
> match the length of the event mask, as per architecture.
> 
> While the default behaviour is to be compliant with the architecture,
> when using older machine models the old broken behaviour is selected
> (allowing only masks of size exactly 4), in order to be able to migrate
> toward older versions.
> 
> Fixes: 67915de9f0383ccf4a ("s390x/event-facility: variable-length event masks")
> Signed-off-by: Claudio Imbrenda <imbrenda@linux.vnet.ibm.com>
> ---
>  hw/s390x/event-facility.c  | 91 +++++++++++++++++++++++++++++++++++++++-------
>  hw/s390x/s390-virtio-ccw.c |  8 +++-
>  2 files changed, 85 insertions(+), 14 deletions(-)

Looks reasonable.