Re: [PATCH v1 5/8] vfio/type1: Report 1st-level/stage-1 format to userspace

[Auger Eric <eric.auger@redhat.com>]

Hi Yi,

On 4/1/20 2:51 PM, Liu, Yi L wrote:
> Hi Eric,
> 
>> From: Auger Eric <eric.auger@redhat.com>
>> Sent: Wednesday, April 1, 2020 4:51 PM
>> To: Liu, Yi L <yi.l.liu@intel.com>; alex.williamson@redhat.com
>> Subject: Re: [PATCH v1 5/8] vfio/type1: Report 1st-level/stage-1 format to
>> userspace
>>
>> Hi Yi,
>> On 3/22/20 1:32 PM, Liu, Yi L wrote:
>>> From: Liu Yi L <yi.l.liu@intel.com>
>>>
>>> VFIO exposes IOMMU nesting translation (a.k.a dual stage translation)
>>> capability to userspace. Thus applications like QEMU could support
>>> vIOMMU with hardware's nesting translation capability for pass-through
>>> devices. Before setting up nesting translation for pass-through devices,
>>> QEMU and other applications need to learn the supported 1st-lvl/stage-1
>>> translation structure format like page table format.
>>>
>>> Take vSVA (virtual Shared Virtual Addressing) as an example, to support
>>> vSVA for pass-through devices, QEMU setup nesting translation for pass-
>>> through devices. The guest page table are configured to host as 1st-lvl/
>>> stage-1 page table. Therefore, guest format should be compatible with
>>> host side.
>>>
>>> This patch reports the supported 1st-lvl/stage-1 page table format on the
>>> current platform to userspace. QEMU and other alike applications should
>>> use this format info when trying to setup IOMMU nesting translation on
>>> host IOMMU.
>>>
>>> Cc: Kevin Tian <kevin.tian@intel.com>
>>> CC: Jacob Pan <jacob.jun.pan@linux.intel.com>
>>> Cc: Alex Williamson <alex.williamson@redhat.com>
>>> Cc: Eric Auger <eric.auger@redhat.com>
>>> Cc: Jean-Philippe Brucker <jean-philippe@linaro.org>
>>> Signed-off-by: Liu Yi L <yi.l.liu@intel.com>
>>> ---
>>>  drivers/vfio/vfio_iommu_type1.c | 56
>> +++++++++++++++++++++++++++++++++++++++++
>>>  include/uapi/linux/vfio.h       |  1 +
>>>  2 files changed, 57 insertions(+)
>>>
>>> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
>>> index 9aa2a67..82a9e0b 100644
>>> --- a/drivers/vfio/vfio_iommu_type1.c
>>> +++ b/drivers/vfio/vfio_iommu_type1.c
>>> @@ -2234,11 +2234,66 @@ static int vfio_iommu_type1_pasid_free(struct
>> vfio_iommu *iommu,
>>>  	return ret;
>>>  }
>>>
>>> +static int vfio_iommu_get_stage1_format(struct vfio_iommu *iommu,
>>> +					 u32 *stage1_format)
>> vfio_pasid_format() to be homogeneous with vfio_pgsize_bitmap() which
>> does the same kind of enumeration of the vfio_iommu domains
> 
> yes, similar.
> 
>>> +{
>>> +	struct vfio_domain *domain;
>>> +	u32 format = 0, tmp_format = 0;
>>> +	int ret;
>> ret = -EINVAL;
> 
> got it.
> 
>>> +
>>> +	mutex_lock(&iommu->lock);
>>> +	if (list_empty(&iommu->domain_list)) {
>> goto out_unlock;
> 
> right.
>>> +		mutex_unlock(&iommu->lock);
>>> +		return -EINVAL;
>>> +	}
>>> +
>>> +	list_for_each_entry(domain, &iommu->domain_list, next) {
>>> +		if (iommu_domain_get_attr(domain->domain,
>>> +			DOMAIN_ATTR_PASID_FORMAT, &format)) {
>> I can find DOMAIN_ATTR_PASID_FORMAT in Jacob's v9 but not in v10
> 
> oops, I guess he somehow missed. you may find it in below link.
> 
> https://github.com/luxis1999/linux-vsva/commit/bf14b11a12f74d58ad3ee626a5d891de395082eb
> 
>>> +			ret = -EINVAL;
>> could be removed
> 
> sure.
> 
>>> +			format = 0;
>>> +			goto out_unlock;
>>> +		}
>>> +		/*
>>> +		 * format is always non-zero (the first format is
>>> +		 * IOMMU_PASID_FORMAT_INTEL_VTD which is 1). For
>>> +		 * the reason of potential different backed IOMMU
>>> +		 * formats, here we expect to have identical formats
>>> +		 * in the domain list, no mixed formats support.
>>> +		 * return -EINVAL to fail the attempt of setup
>>> +		 * VFIO_TYPE1_NESTING_IOMMU if non-identical formats
>>> +		 * are detected.
>>> +		 */
>>> +		if (tmp_format && tmp_format != format) {
>>> +			ret = -EINVAL;
>> could be removed
> 
> got it.
> 
>>> +			format = 0;
>>> +			goto out_unlock;
>>> +		}
>>> +
>>> +		tmp_format = format;
>>> +	}
>>> +	ret = 0;
>>> +
>>> +out_unlock:
>>> +	if (format)
>> if (!ret) ? then you can remove the format = 0 in case of error.
> 
> oh, yes.
> 
>>> +		*stage1_format = format;
>>> +	mutex_unlock(&iommu->lock);
>>> +	return ret;
>>> +}
>>> +
>>>  static int vfio_iommu_info_add_nesting_cap(struct vfio_iommu *iommu,
>>>  					 struct vfio_info_cap *caps)
>>>  {
>>>  	struct vfio_info_cap_header *header;
>>>  	struct vfio_iommu_type1_info_cap_nesting *nesting_cap;
>>> +	u32 formats = 0;
>>> +	int ret;
>>> +
>>> +	ret = vfio_iommu_get_stage1_format(iommu, &formats);
>>> +	if (ret) {
>>> +		pr_warn("Failed to get stage-1 format\n");
>> trace triggered by userspace to be removed?
> 
> sure.
> 
>>> +		return ret;
>>> +	}
>>>
>>>  	header = vfio_info_cap_add(caps, sizeof(*nesting_cap),
>>>  				   VFIO_IOMMU_TYPE1_INFO_CAP_NESTING, 1);
>>> @@ -2254,6 +2309,7 @@ static int vfio_iommu_info_add_nesting_cap(struct
>> vfio_iommu *iommu,
>>>  		/* nesting iommu type supports PASID requests (alloc/free) */
>>>  		nesting_cap->nesting_capabilities |= VFIO_IOMMU_PASID_REQS;
>> What is the meaning for ARM?
> 
> I think it's just a software capability exposed to userspace, on
> userspace side, it has a choice to use it or not. :-) The reason
> define it and report it in cap nesting is that I'd like to make
> the pasid alloc/free be available just for IOMMU with type
> VFIO_IOMMU_TYPE1_NESTING. Please feel free tell me if it is not
> good for ARM. We can find a proper way to report the availability.

Well it is more a question for jean-Philippe. Do we have a system wide
PASID allocation on ARM?

Thanks

Eric
> 
>>>  	}
>>> +	nesting_cap->stage1_formats = formats;
>> as spotted by Kevin, since a single format is supported, rename
> 
> ok, I was believing it may be possible on ARM or so. :-) will
> rename it.
> 
> I'll refine the patch per your above comments.
> 
> Regards,
> Yi Liu
>