Re: [PATCH v3 09/16] iommu: Introduce guest PASID bind function

Jacob Pan
2019-05-21T22:47:36Z

On Tue, 21 May 2019 17:09:40 +0100
Jean-Philippe Brucker <jean-philippe.brucker@arm.com> wrote:

> On 20/05/2019 20:22, Jacob Pan wrote:
> > On Thu, 16 May 2019 09:14:29 -0700
> > Jacob Pan <jacob.jun.pan@linux.intel.com> wrote:
> >
> >> On Thu, 16 May 2019 15:14:40 +0100
> >> Jean-Philippe Brucker <jean-philippe.brucker@arm.com> wrote:
> >>
> >>> Hi Jacob,
> >>>
> >>> On 03/05/2019 23:32, Jacob Pan wrote:
> >>>> +/**
> >>>> + * struct gpasid_bind_data - Information about device and guest
> >>>> PASID binding
> >>>> + * @gcr3: Guest CR3 value from guest mm
> >>>> + * @pasid: Process address space ID used for the guest mm
> >>>> + * @addr_width: Guest address width. Paging mode can also
> >>>> be derived.
> >>>> + */
> >>>> +struct gpasid_bind_data {
> >>>> + __u64 gcr3;
> >>>> + __u32 pasid;
> >>>> + __u32 addr_width;
> >>>> + __u32 flags;
> >>>> +#define IOMMU_SVA_GPASID_SRE BIT(0) /* supervisor
> >>>> request */
> >>>> + __u8 padding[4];
> >>>> +};
> >>>
> >>> Could you wrap this structure into a generic one like we now do
> >>> for bind_pasid_table? It would make the API easier to extend,
> >>> because if we ever add individual PASID bind on Arm (something
> >>> I'd like to do for virtio-iommu, eventually) it will have
> >>> different parameters, as our PASID table entry has a lot of
> >>> fields describing the page table format.
> >>>
> >>> Maybe something like the following would do?
> >>>
> >>> struct gpasid_bind_data {
> >>> #define IOMMU_GPASID_BIND_VERSION_1 1
> >>> __u32 version;
> >>> #define IOMMU_GPASID_BIND_FORMAT_INTEL_VTD 1
> >>> __u32 format;
> >>> union {
> >>> // the current gpasid_bind_data:
> >>> struct gpasid_bind_intel_vtd vtd;
> >>> };
> >>> };
> >>>
> >
> > Could you review the struct below? I am trying to extract the
> > common fileds as much as possible. Didn't do exactly as you
> > suggested to keep vendor specific data in separate struct under the
> > same union.
>
> Thanks, it looks good and I think we can reuse it for SMMUv2 and v3.
> Some comments below.
>
> >
> > Also, can you review the v3 ioasid allocator common code patches? I
> > am hoping we can get the common code in v5.3 so that we can focus
> > on the vendor specific part. The common code should include
> > bind_guest_pasid and ioasid allocator.
> > https://lkml.org/lkml/2019/5/3/787
> > https://lkml.org/lkml/2019/5/3/780
> >
> > Thanks,
> >
> > Jacob
> >
> >
> > /**
> > * struct gpasid_bind_data_vtd - Intel VT-d specific data on device
> > and guest
> > * SVA binding.
> > *
> > * @flags: VT-d PASID table entry attributes
> > * @pat: Page attribute table data to compute effective
> > memory type
> > * @emt: Extended memory type
> > *
> > * Only guest vIOMMU selectable and effective options are passed
> > down to
> > * the host IOMMU.
> > */
> > struct gpasid_bind_data_vtd {
> > #define IOMMU_SVA_VTD_GPASID_SRE BIT(0) /* supervisor
> > request */ #define IOMMU_SVA_VTD_GPASID_EAFE
> > BIT(1) /* extended access enable */ #define
> > IOMMU_SVA_VTD_GPASID_PCD BIT(2) /* page-level cache disable
> > */ #define IOMMU_SVA_VTD_GPASID_PWT BIT(3) /*
> > page-level write through */ #define
> > IOMMU_SVA_VTD_GPASID_EMTE BIT(4) /* extended memory type
> > enable */ #define IOMMU_SVA_VTD_GPASID_CD
> > BIT(5) /* PASID-level cache disable */
>
> It doesn't seem like the BIT() macro is exported to userspace, so we
> can't use it here
>
good point, will avoid BIT()
> > __u64 flags;
> > __u32 pat;
> > __u32 emt;
> > };
> >
> > /**
> > * struct gpasid_bind_data - Information about device and guest
> > PASID binding
> > * @version: Version of this data structure
> > * @format: PASID table entry format
> > * @flags: Additional information on guest bind request
> > * @gpgd: Guest page directory base of the guest mm to bind
> > * @hpasid: Process address space ID used for the guest mm
> > in host IOMMU
> > * @gpasid: Process address space ID used for the guest mm
> > in guest IOMMU
>
> Trying to understand the full flow:
> * @gpasid is the one allocated by the guest using a virtual command.
> The guest writes @gpgd into the virtual PASID table at index @gpasid,
> then sends an invalidate command to QEMU.
yes
> * QEMU issues a gpasid_bind ioctl (on the mdev or its container?).
> VFIO forwards. The IOMMU driver installs @gpgd into the PASID table
> using @hpasid, which is associated with the auxiliary domain.
>
> But why do we need the @hpasid field here? Does userspace know about
> it at all, and does VFIO need to pass it to the IOMMU driver?
>
We need to support two guest-host PASID mappings through this API. Idea
comes from Kevin & Yi.
1. identity mapping between host and guest PASID
2. guest owns its own pasid space

For option 1, which will plan to support first in this series. There is
no need for gpasid field since gpasid=hpasid. Guest allocates PASID
using virtual command interface which gets a host PASID. Then PASID
cache invalidation in the guest will result in bind_gpasid(), @gpasid is
not valid in the bind data (indicated by the IOMMU_SVA_GPASID_VAL flag).

For option 2, guest still uses virtual command to allocate guest pasid,
but this time QEMU does the allocation for gpasid, at the same time
QEMU will allocate a host pasid then maintain a G->H PASID lookup.
When guest invalidate its PASID cache with GPASID, QEMU will find the
match host PASID then pass both gpasid and hpasid down to the host IOMMU
driver.
Host IOMMU driver will store the gpgd at the hpasid entry but keep
track of the gpasid->hpasid mapping. Host will never program gpasid in
the IOMMU HW. Host IOMMU driver provides G->H PASID translation for PF
device drivers that emulates mdev config space, i.e. virtual device
composition module
(https://events.linuxfoundation.org/wp-content/uploads/2017/12/Hardware-Assisted-Mediated-Pass-Through-with-VFIO-Kevin-Tian-Intel.pdf).

These two options is a per VM choice. Hopefully the two diagrams below
can help to explain. I will put them in the next patch headers.

Option 1. Identity G-H PASID mapping diagram.

.-------------. .---------------------------.
| vIOMMU | | Guest process mm, FL only |
| | '---------------------------'
.----------------/
| PASID Entry |--- PASID cache flush -
'-------------'\ |
| | \ |
| | \ |
'-------------' \________________ |
GPASID = HPASID |
Guest ^ ^ |
------| Shadow |-------| VCMD |-----------|------------
v v | | |
QEMU v v |
------------------------------------------|------------
Host HPASID = ioasid_alloc() |
| v
| sva_bind_gpasid(HPASID)
|
.-------------. | .----------------------.
| pIOMMU | | | Bind FL for GVA-GPA |
| | | /'----------------------'
.----------------' |
| PASID Entry | V (Nested xlate)
'----------------..---------------------.
| | |Set SL to GPA-HPA |
| | '---------------------'
'-------------'

Option 2. Non-identity G-H PASID mapping diagram.

.-------------. .---------------------------.
| vIOMMU | | Guest process mm, FL only |
| | '---------------------------'
.----------------/
| PASID Entry |--- PASID cache flush -
'-------------'\ | .-------------.
| | \ | |Guest driver |
| | \ | |writes GPASID|
'-------------' \________________ | '-------------'
GPASID | |
Guest ^ ^ | |
------| Shadow |-------| VCMD |-----------|------------ |
v v | | | |
QEMU v v | |
GPASID = qemu_gpasid_alloc() | |
keep G->H PASID lookup | |
^ v |
| lookup G->H PASID |
-------------------|----------------------|------------ |
Host HPASID = ioasid_alloc() | |
| v |
| sva_bind_gpasid(HPASID,GPASID)|
| keep H-G PASID lookup |
| \ -------------------.
.-------------. | .----------------------. \| VDCM |
| pIOMMU | | | Bind FL for GVA-GPA | | H = lookup(GPASID)|
| | | /'----------------------' | write H to dev |
.----------------' | '------------------'
| PASID Entry | V (Nested xlate)
'----------------..---------------------.
| | |Set SL to GPA-HPA |
| | '---------------------'
'-------------'
There is also implications in G-H pasid lookup for PRQ, that would be
in the later series.

> > * @addr_width: Guest address width. Paging mode can also be
> > derived.
>
> What does the last sentence mean? @addr_width should probably be in
> @vtd if it provides implicit information.
>
Derive 4 or 5 level paging mode from the address width. It can be in
@vtd but i thought this can be generic.

> > * @vtd: Intel VT-d specific data
> > */
> > struct gpasid_bind_data {
> > #define IOMMU_GPASID_BIND_VERSION_1 1
> > __u32 version;
> > #define IOMMU_PASID_FORMAT_INTEL_VTD 1
> > __u32 format;
> > #define IOMMU_SVA_GPASID_VAL BIT(1) /* guest PASID
> > valid */
>
> (There are tabs between define and name here, as well as in the VT-d
> specific data)
>
> > __u64 flags;
> > __u64 gpgd;
> > __u64 hpasid;
> > __u64 gpasid;
> > __u32 addr_width;
>
> I think the union has to be aligned on 64-bit, otherwise a compiler
> might insert padding (https://lkml.org/lkml/2019/1/11/1207)
>
good point, will fix.
> Thanks,
> Jean
>
> > /* Vendor specific data */
> > union {
> > struct gpasid_bind_data_vtd vtd;
> > };
> > };
> >
> >
>

[Jacob Pan]