Linux Virtualization - May 2019 - [PATCH 08/10] virtio/s390: add indirection to indicators access

On 09/05/2019 20:26, Halil Pasic wrote:
> On Thu, 9 May 2019 14:01:01 +0200
> Pierre Morel <pmorel at 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 at 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?

Pierre

-- 
Pierre Morel
Linux/KVM/QEMU in B?blingen - Germany

On Fri, 10 May 2019 09:43:08 +0200
Pierre Morel <pmorel at 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 at 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 at 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

On 10/05/2019 13:54, Halil Pasic wrote:
> On Fri, 10 May 2019 09:43:08 +0200
> Pierre Morel <pmorel at 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 at 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 at
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?
> 
I did not wanted to discuss a long time on this and gave my R-B, so 
meaning that I am OK with this patch.

But if you ask, yes I can, it seems quite obvious.
When you build a CCW you give the pointer to CCW->cda and you give the 
size of the transfer in CCW->count.

Here the count is initialized with the sizeof of the pointer used to 
initialize CCW->cda with.
Lukily we work on a 64 bits machine with 64 bits pointers and the size 
of the pointed object is 64 bits wide so... the resulting count is right.
But it is not the correct way to do it.
That is all. Not a big concern, you do not need to change it, as you 
said it can be done in another patch.
> Did you agree with the rest of my comment? I mean there was more to it.
> 
I understood from your comments that the indicators in Linux are 64bits 
wide so all OK.

Regards
Pierre






-- 
Pierre Morel
Linux/KVM/QEMU in B?blingen - Germany