Re: [PATCH 08/10] virtio/s390: add indirection to indicators access

[Halil Pasic <pasic@linux.ibm.com>]

On Fri, 10 May 2019 09:43:08 +0200
Pierre Morel <pmorel@linux.ibm.com> wrote:

> On 09/05/2019 20:26, Halil Pasic wrote:
> > On Thu, 9 May 2019 14:01:01 +0200
> > Pierre Morel <pmorel@linux.ibm.com> wrote:
> > 
> >> On 08/05/2019 16:31, Pierre Morel wrote:
> >>> On 26/04/2019 20:32, Halil Pasic wrote:
> >>>> This will come in handy soon when we pull out the indicators from
> >>>> virtio_ccw_device to a memory area that is shared with the hypervisor
> >>>> (in particular for protected virtualization guests).
> >>>>
> >>>> Signed-off-by: Halil Pasic <pasic@linux.ibm.com>
> >>>> ---
> >>>>    drivers/s390/virtio/virtio_ccw.c | 40
> >>>> +++++++++++++++++++++++++---------------
> >>>>    1 file changed, 25 insertions(+), 15 deletions(-)
> >>>>
> >>>> diff --git a/drivers/s390/virtio/virtio_ccw.c
> >>>> b/drivers/s390/virtio/virtio_ccw.c
> >>>> index bb7a92316fc8..1f3e7d56924f 100644
> >>>> --- a/drivers/s390/virtio/virtio_ccw.c
> >>>> +++ b/drivers/s390/virtio/virtio_ccw.c
> >>>> @@ -68,6 +68,16 @@ struct virtio_ccw_device {
> >>>>        void *airq_info;
> >>>>    };
> >>>> +static inline unsigned long *indicators(struct virtio_ccw_device *vcdev)
> >>>> +{
> >>>> +    return &vcdev->indicators;
> >>>> +}
> >>>> +
> >>>> +static inline unsigned long *indicators2(struct virtio_ccw_device
> >>>> *vcdev)
> >>>> +{
> >>>> +    return &vcdev->indicators2;
> >>>> +}
> >>>> +
> >>>>    struct vq_info_block_legacy {
> >>>>        __u64 queue;
> >>>>        __u32 align;
> >>>> @@ -337,17 +347,17 @@ static void virtio_ccw_drop_indicator(struct
> >>>> virtio_ccw_device *vcdev,
> >>>>            ccw->cda = (__u32)(unsigned long) thinint_area;
> >>>>        } else {
> >>>>            /* payload is the address of the indicators */
> >>>> -        indicatorp = kmalloc(sizeof(&vcdev->indicators),
> >>>> +        indicatorp = kmalloc(sizeof(indicators(vcdev)),
> >>>>                         GFP_DMA | GFP_KERNEL);
> >>>>            if (!indicatorp)
> >>>>                return;
> >>>>            *indicatorp = 0;
> >>>>            ccw->cmd_code = CCW_CMD_SET_IND;
> >>>> -        ccw->count = sizeof(&vcdev->indicators);
> >>>> +        ccw->count = sizeof(indicators(vcdev));
> >>>
> >>> This looks strange to me. Was already weird before.
> >>> Lucky we are indicators are long...
> >>> may be just sizeof(long)
> >>
> > 
> > I'm not sure I understand where are you coming from...
> > 
> > With CCW_CMD_SET_IND we tell the hypervisor the guest physical address
> > at which the so called classic indicators. There is a comment that
> > makes this obvious. The argument of the sizeof was and remained a
> > pointer type. AFAIU this is what bothers you.
> >>
> >> AFAIK the size of the indicators (AIV/AIS) is not restricted by the
> >> architecture.
> > 
> > The size of vcdev->indicators is restricted or defined by the virtio
> > specification. Please have a look at '4.3.2.6.1 Setting Up Classic Queue
> > Indicators' here:
> > https://docs.oasis-open.org/virtio/virtio/v1.1/cs01/virtio-v1.1-cs01.html#x1-1630002
> > 
> > Since with Linux on s390 only 64 bit is supported, both the sizes are in
> > line with the specification. Using u64 would semantically match the spec
> > better, modulo pre virtio 1.0 which ain't specified. I did not want to
> > do changes that are not necessary for what I'm trying to accomplish. If
> > we want we can change these to u64 with a patch on top.
> 
> I mean you are changing these line already, so why not doing it right 
> while at it?
> 

This patch is about adding the indirection so we can move the member
painlessly. Mixing in different stuff would be a bad practice.

BTW I just explained that it ain't wrong, so I really do not understand
what do you mean by  'why not doing it right'. Can you please explain?

Did you agree with the rest of my comment? I mean there was more to it.

Regards,
Halil

_______________________________________________
Virtualization mailing list
Virtualization@lists.linux-foundation.org
https://lists.linuxfoundation.org/mailman/listinfo/virtualization