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

Jean-Philippe Brucker
2019-05-21T16:10:07Z

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

> __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.
* 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?

> * @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.

> * @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)

Thanks,
Jean

> /* Vendor specific data */
> union {
> struct gpasid_bind_data_vtd vtd;
> };
> };