linux-kernel - Re: [PATCH 08/12] iommufd/device: Report supported hwpt

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Date:   Thu, 9 Mar 2023 23:10:02 -0800
From:   Nicolin Chen <nicolinc@...dia.com>
To:     Baolu Lu <baolu.lu@...ux.intel.com>
CC:     Yi Liu <yi.l.liu@...el.com>, <joro@...tes.org>,
        <alex.williamson@...hat.com>, <jgg@...dia.com>,
        <kevin.tian@...el.com>, <robin.murphy@....com>,
        <cohuck@...hat.com>, <eric.auger@...hat.com>,
        <kvm@...r.kernel.org>, <mjrosato@...ux.ibm.com>,
        <chao.p.peng@...ux.intel.com>, <yi.y.sun@...ux.intel.com>,
        <peterx@...hat.com>, <jasowang@...hat.com>,
        <shameerali.kolothum.thodi@...wei.com>, <lulu@...hat.com>,
        <suravee.suthikulpanit@....com>, <iommu@...ts.linux.dev>,
        <linux-kernel@...r.kernel.org>, <linux-kselftest@...r.kernel.org>
Subject: Re: [PATCH 08/12] iommufd/device: Report supported hwpt_types

On Fri, Mar 10, 2023 at 11:30:04AM +0800, Baolu Lu wrote:
> External email: Use caution opening links or attachments
> 
> 
> On 3/9/23 4:09 PM, Yi Liu wrote:
> > This provides a way for userspace to probe the supported hwpt data
> > types by kernel. Currently, kernel only supports IOMMU_HWPT_TYPE_DEFAULT,
> > new types would be added per vendor drivers' extension.
> > 
> > Userspace that wants to allocate hw_pagetable with user data should check
> > this. While for the allocation without user data, no need for it. It is
> > supported by default.
> > 
> > Co-developed-by: Nicolin Chen <nicolinc@...dia.com>
> > Signed-off-by: Nicolin Chen <nicolinc@...dia.com>
> > Signed-off-by: Yi Liu <yi.l.liu@...el.com>
> > ---
> >   drivers/iommu/iommufd/device.c          |  1 +
> >   drivers/iommu/iommufd/hw_pagetable.c    | 18 +++++++++++++++---
> >   drivers/iommu/iommufd/iommufd_private.h |  2 ++
> >   drivers/iommu/iommufd/main.c            |  2 +-
> >   include/uapi/linux/iommufd.h            |  8 ++++++++
> >   5 files changed, 27 insertions(+), 4 deletions(-)
> > 
> > diff --git a/drivers/iommu/iommufd/device.c b/drivers/iommu/iommufd/device.c
> > index 19cd6df46c6a..0328071dcac1 100644
> > --- a/drivers/iommu/iommufd/device.c
> > +++ b/drivers/iommu/iommufd/device.c
> > @@ -322,6 +322,7 @@ int iommufd_device_get_hw_info(struct iommufd_ucmd *ucmd)
> > 
> >       cmd->out_data_type = ops->driver_type;
> >       cmd->data_len = length;
> > +     cmd->out_hwpt_type_bitmap = iommufd_hwpt_type_bitmaps[ops->driver_type];
> > 
> >       rc = iommufd_ucmd_respond(ucmd, sizeof(*cmd));
> > 
> > diff --git a/drivers/iommu/iommufd/hw_pagetable.c b/drivers/iommu/iommufd/hw_pagetable.c
> > index 67facca98de1..160712256c64 100644
> > --- a/drivers/iommu/iommufd/hw_pagetable.c
> > +++ b/drivers/iommu/iommufd/hw_pagetable.c
> > @@ -173,6 +173,14 @@ static const size_t iommufd_hwpt_alloc_data_size[] = {
> >       [IOMMU_HWPT_TYPE_DEFAULT] = 0,
> >   };
> > 
> > +/*
> > + * bitmaps of supported hwpt types of by underlying iommu, indexed
> > + * by ops->driver_type which is one of enum iommu_hw_info_type.
> > + */
> > +const u64 iommufd_hwpt_type_bitmaps[] =  {
> > +     [IOMMU_HW_INFO_TYPE_DEFAULT] = BIT_ULL(IOMMU_HWPT_TYPE_DEFAULT),
> > +};
> 
> I am a bit confused here. Why do you need this array? What I read is
> that you want to convert ops->driver_type to a bit position in
> cmd->out_hwpt_type_bitmap.
> 
> Am I getting it right?
> 
> If so, why not just
>        cmd->out_hwpt_type_bitmap = BIT_ULL(ops->driver_type);
> 
> ?

A driver_type would be IOMMUFD_HW_INFO_TYPExx. What's inside the
BIT_ULL is IOMMUFD_HWPT_TYPE_*. It seems to get a bit confusing
after several rounds of renaming though. And they do seem to be
a bit of duplications at the actual values, at least for now.

I recall that we only had one enum for the types, yet later did
a separation into driver_types and hwpt_types after a discussion
regarding future PASID support?

Thanks
Nic