Re: [PATCH 4/4] vfio: vfio_iommu_type1: implement VFIO_IOMMU_INFO_CAPABILITIES

Pierre Morel
2019-05-17T08:17:17Z

On 16/05/2019 20:40, Alex Williamson wrote:
> On Fri, 10 May 2019 10:22:35 +0200
> Pierre Morel <pmorel@linux.ibm.com> wrote:
>
>> We implement a capability intercafe for VFIO_IOMMU_GET_INFO and add the
>> first capability: VFIO_IOMMU_INFO_CAPABILITIES.
>>
>> When calling the ioctl, the user must specify
>> VFIO_IOMMU_INFO_CAPABILITIES to retrieve the capabilities and must check
>> in the answer if capabilities are supported.
>> Older kernel will not check nor set the VFIO_IOMMU_INFO_CAPABILITIES in
>> the flags of vfio_iommu_type1_info.
>>
>> The iommu get_attr callback will be called to retrieve the specific
>> attributes and fill the capabilities, VFIO_IOMMU_INFO_CAP_QFN for the
>> PCI query function attributes and VFIO_IOMMU_INFO_CAP_QGRP for the
>> PCI query function group.
>>
>> Signed-off-by: Pierre Morel <pmorel@linux.ibm.com>
>> ---
>> drivers/vfio/vfio_iommu_type1.c | 95 ++++++++++++++++++++++++++++++++++++++++-
>> 1 file changed, 94 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
>> index d0f731c..f7f8120 100644
>> --- a/drivers/vfio/vfio_iommu_type1.c
>> +++ b/drivers/vfio/vfio_iommu_type1.c
>> @@ -1658,6 +1658,70 @@ static int vfio_domains_have_iommu_cache(struct vfio_iommu *iommu)
>> return ret;
>> }
>>
>> +int vfio_iommu_type1_caps(struct vfio_iommu *iommu, struct vfio_info_cap *caps,
>> + size_t size)
>> +{
>> + struct vfio_domain *d;
>> + struct vfio_iommu_type1_info_block *info_fn;
>> + struct vfio_iommu_type1_info_block *info_grp;
>> + unsigned long total_size, fn_size, grp_size;
>> + int ret;
>> +
>> + d = list_first_entry(&iommu->domain_list, struct vfio_domain, next);
>> + if (!d)
>> + return -ENODEV;
>> + /* The size of these capabilities are device dependent */
>> + fn_size = iommu_domain_get_attr(d->domain,
>> + DOMAIN_ATTR_ZPCI_FN_SIZE, NULL);
>> + if (fn_size < 0)
>> + return fn_size;
>
> What if non-Z archs want to use this? The function is architected
> specifically for this one use case, fail if any component is not there
> which means it requires a re-write to add further support. If
> ZPCI_FN_SIZE isn't support, move on to the next thing.

yes, clear.

>
>> + fn_size += sizeof(struct vfio_info_cap_header);
>> + total_size = fn_size;
>
> Here too, total_size should be initialized to zero and each section +=
> the size they'd like to add.

thanks, clear too.

>
>> +
>> + grp_size = iommu_domain_get_attr(d->domain,
>> + DOMAIN_ATTR_ZPCI_GRP_SIZE, NULL);
>> + if (grp_size < 0)
>> + return grp_size;
>> + grp_size += sizeof(struct vfio_info_cap_header);
>> + total_size += grp_size;
>> +
>> + /* Tell caller to call us with a greater buffer */
>> + if (total_size > size) {
>> + caps->size = total_size;
>> + return 0;
>> + }
>> +
>> + info_fn = kzalloc(fn_size, GFP_KERNEL);
>> + if (!info_fn)
>> + return -ENOMEM;
>
> Maybe fn_size was zero because we're not on Z.
>
>> + ret = iommu_domain_get_attr(d->domain,
>> + DOMAIN_ATTR_ZPCI_FN, &info_fn->data);
>
> Kernel internal structures != user api. Thanks,
>
> Alex

Thanks a lot Alex,
I understand the concerns, I was too focussed on Z, I will rework this
as you said:
- definition of the user API and
- take care that another architecture may want to use the interface.

Regards,
Pierre

--
Pierre Morel
Linux/KVM/QEMU in Böblingen - Germany