From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Reply-To: pmorel@linux.ibm.com Subject: Re: [PATCH 08/10] virtio/s390: add indirection to indicators access References: <20190426183245.37939-1-pasic@linux.ibm.com> <20190426183245.37939-9-pasic@linux.ibm.com> <716d47ca-016f-e8f4-6d78-7746a7d9f6ba@linux.ibm.com> <20190509202600.4fd6aebe.pasic@linux.ibm.com> <20190510135421.5363f14a.pasic@linux.ibm.com> <89074bc5-78ee-a2e3-0546-791a465f83bd@linux.ibm.com> <20190513121502.34d3dc62.cohuck@redhat.com> From: Pierre Morel Date: Thu, 16 May 2019 17:24:39 +0200 MIME-Version: 1.0 In-Reply-To: <20190513121502.34d3dc62.cohuck@redhat.com> Content-Type: text/plain; charset="utf-8"; format="flowed" Content-Language: en-US Content-Transfer-Encoding: 8bit Message-Id: <2736e862-69e5-7923-b429-aee0dcdd2c5a@linux.ibm.com> Sender: kvm-owner@vger.kernel.org List-Archive: List-Post: To: Cornelia Huck Cc: Halil Pasic , kvm@vger.kernel.org, linux-s390@vger.kernel.org, Martin Schwidefsky , Sebastian Ott , virtualization@lists.linux-foundation.org, "Michael S. Tsirkin" , Christoph Hellwig , Thomas Huth , Christian Borntraeger , Viktor Mihajlovski , Vasily Gorbik , Janosch Frank , Claudio Imbrenda , Farhan Ali , Eric Farman List-ID: On 13/05/2019 12:15, Cornelia Huck wrote: > On Fri, 10 May 2019 17:36:05 +0200 > Pierre Morel wrote: > >> On 10/05/2019 13:54, Halil Pasic wrote: >>> On Fri, 10 May 2019 09:43:08 +0200 >>> Pierre Morel wrote: >>> >>>> On 09/05/2019 20:26, Halil Pasic wrote: >>>>> On Thu, 9 May 2019 14:01:01 +0200 >>>>> Pierre Morel 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 >>>>>>>> --- >>>>>>>>   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. > > But the cda points to the pointer address, so the size of the pointer > is actually the correct value here, isn't it? Oh. Yes, it is correct. What I do not like are the mixing of (unsigned long), (unsigned long *) and & if we had cda = _u32 (unsigned long) indicatorp count = sizeof(*indicatorp) I would have been completely happy. It was just a non important thing and I wouldn't have given a R-B if the functionality was not correct. > >> 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. > > I think it is, but this interface really is confusing. Yes, it is what I thought we could do better. > >> 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 Böblingen - Germany