RE: [PATCH v4 04/15] vfio/type1: Report iommu nesting info to userspace

From: "Liu, Yi L" <yi.l.liu@intel.com>
To: Auger Eric <eric.auger@redhat.com>,
	"alex.williamson@redhat.com" <alex.williamson@redhat.com>,
	"baolu.lu@linux.intel.com" <baolu.lu@linux.intel.com>,
	"joro@8bytes.org" <joro@8bytes.org>
Cc: "Tian, Kevin" <kevin.tian@intel.com>,
	"jacob.jun.pan@linux.intel.com" <jacob.jun.pan@linux.intel.com>,
	"Raj, Ashok" <ashok.raj@intel.com>,
	"Tian, Jun J" <jun.j.tian@intel.com>,
	"Sun, Yi Y" <yi.y.sun@intel.com>,
	"jean-philippe@linaro.org" <jean-philippe@linaro.org>,
	"peterx@redhat.com" <peterx@redhat.com>,
	"Wu, Hao" <hao.wu@intel.com>,
	"stefanha@gmail.com" <stefanha@gmail.com>,
	"iommu@lists.linux-foundation.org"
	<iommu@lists.linux-foundation.org>,
	"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: RE: [PATCH v4 04/15] vfio/type1: Report iommu nesting info to userspace
Date: Wed, 8 Jul 2020 08:08:40 +0000	[thread overview]
Message-ID: <DM5PR11MB143531E2B54ED82FB0649F8CC3670@DM5PR11MB1435.namprd11.prod.outlook.com> (raw)
In-Reply-To: <DM5PR11MB14357A5953EB630A58FF568EC3660@DM5PR11MB1435.namprd11.prod.outlook.com>

Hi Alex,

Eric asked if we will to have data strcut other than struct iommu_nesting_info
type in the struct vfio_iommu_type1_info_cap_nesting @info[] field. I'm not
quit sure on it. I guess the answer may be not as VFIO's nesting support should
based on IOMMU UAPI. how about your opinion?

+#define VFIO_IOMMU_TYPE1_INFO_CAP_NESTING  3
+
+/*
+ * Reporting nesting info to user space.
+ *
+ * @info:	the nesting info provided by IOMMU driver. Today
+ *		it is expected to be a struct iommu_nesting_info
+ *		data.
+ */
+struct vfio_iommu_type1_info_cap_nesting {
+	struct	vfio_info_cap_header header;
+	__u32	flags;
+	__u32	padding;
+	__u8	info[];
+};

https://lore.kernel.org/linux-iommu/DM5PR11MB1435290B6CD561EC61027892C3690@DM5PR11MB1435.namprd11.prod.outlook.com/

Regards,
Yi Liu

> From: Liu, Yi L
> Sent: Tuesday, July 7, 2020 5:32 PM
> 
[...]
> > >
> > >>> +
> > >>> +/*
> > >>> + * Reporting nesting info to user space.
> > >>> + *
> > >>> + * @info:	the nesting info provided by IOMMU driver. Today
> > >>> + *		it is expected to be a struct iommu_nesting_info
> > >>> + *		data.
> > >> Is it expected to change?
> > >
> > > honestly, I'm not quite sure on it. I did considered to embed struct
> > > iommu_nesting_info here instead of using info[]. but I hesitated as
> > > using info[] may leave more flexibility on this struct. how about
> > > your opinion? perhaps it's fine to embed the struct
> > > iommu_nesting_info here as long as VFIO is setup nesting based on
> > > IOMMU UAPI.
> > >
> > >>> + */
> > >>> +struct vfio_iommu_type1_info_cap_nesting {
> > >>> +	struct	vfio_info_cap_header header;
> > >>> +	__u32	flags;
> > >> You may document flags.
> > >
> > > sure. it's reserved for future.
> > >
> > > Regards,
> > > Yi Liu
> > >
> > >>> +	__u32	padding;
> > >>> +	__u8	info[];
> > >>> +};
> > >>> +
> > >>>  #define VFIO_IOMMU_GET_INFO _IO(VFIO_TYPE, VFIO_BASE + 12)
> > >>>
> > >>>  /**
> > >>>
> > >> Thanks
> > >>
> > >> Eric
> > >