linux-kernel - Re: [PATCH RFCv1 04/14] iommufd: Add struct iommufd_viommu and iommufd_viommu

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date: Wed, 22 May 2024 17:57:26 +0800
From: Baolu Lu <baolu.lu@...ux.intel.com>
To: "Tian, Kevin" <kevin.tian@...el.com>, Jason Gunthorpe <jgg@...dia.com>,
 Nicolin Chen <nicolinc@...dia.com>
Cc: baolu.lu@...ux.intel.com, "will@...nel.org" <will@...nel.org>,
 "robin.murphy@....com" <robin.murphy@....com>,
 "suravee.suthikulpanit@....com" <suravee.suthikulpanit@....com>,
 "joro@...tes.org" <joro@...tes.org>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
 "linux-arm-kernel@...ts.infradead.org"
 <linux-arm-kernel@...ts.infradead.org>,
 "linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
 "Liu, Yi L" <yi.l.liu@...el.com>,
 "eric.auger@...hat.com" <eric.auger@...hat.com>,
 "vasant.hegde@....com" <vasant.hegde@....com>,
 "jon.grimm@....com" <jon.grimm@....com>,
 "santosh.shukla@....com" <santosh.shukla@....com>,
 "Dhaval.Giani@....com" <Dhaval.Giani@....com>,
 "shameerali.kolothum.thodi@...wei.com" <shameerali.kolothum.thodi@...wei.com>
Subject: Re: [PATCH RFCv1 04/14] iommufd: Add struct iommufd_viommu and
 iommufd_viommu_ops

On 2024/5/22 16:58, Tian, Kevin wrote:
>> From: Jason Gunthorpe<jgg@...dia.com>
>> Sent: Tuesday, May 14, 2024 11:56 PM
>>
>> On Sun, May 12, 2024 at 08:34:02PM -0700, Nicolin Chen wrote:
>>> On Sun, May 12, 2024 at 11:03:53AM -0300, Jason Gunthorpe wrote:
>>>> On Fri, Apr 12, 2024 at 08:47:01PM -0700, Nicolin Chen wrote:
>>>>> Add a new iommufd_viommu core structure to represent a vIOMMU
>> instance in
>>>>> the user space, typically backed by a HW-accelerated feature of an
>> IOMMU,
>>>>> e.g. NVIDIA CMDQ-Virtualization (an ARM SMMUv3 extension) and
>> AMD Hardware
>>>>> Accelerated Virtualized IOMMU (vIOMMU).
>>>> I expect this will also be the only way to pass in an associated KVM,
>>>> userspace would supply the kvm when creating the viommu.
>>>>
>>>> The tricky bit of this flow is how to manage the S2. It is necessary
>>>> that the S2 be linked to the viommu:
>>>>
>>>>   1) ARM BTM requires the VMID to be shared with KVM
>>>>   2) AMD and others need the S2 translation because some of the HW
>>>>      acceleration is done inside the guest address space
>>>>
>>>> I haven't looked closely at AMD but presumably the VIOMMU create will
>>>> have to install the S2 into a DID or something?
>>>>
>>>> So we need the S2 to exist before the VIOMMU is created, but the
>>>> drivers are going to need some more fixing before that will fully
>>>> work.
> Can you elaborate on this point? VIOMMU is a dummy container when
> it's created and the association to S2 comes relevant only until when
> VQUEUE is created inside and linked to a device? then there should be
> a window in between allowing the userspace to configure S2.
> 
> Not saying against setting S2 up before vIOMMU creation. Just want
> to better understand the rationale here.
> 
>>>> Does the nesting domain create need the viommu as well (in place of
>>>> the S2 hwpt)? That feels sort of natural.
>>> Yes, I had a similar thought initially: each viommu is backed by
>>> a nested IOMMU HW, and a special HW accelerator like VCMDQ could
>>> be treated as an extension on top of that. It might not be very
>>> straightforward like the current design having vintf<->viommu and
>>> vcmdq <-> vqueue though...
>> vqueue should be considered a sub object of the viommu and hold a
>> refcount on the viommu object for its lifetime.
>>
>>> In that case, we can then support viommu_cache_invalidate, which
>>> is quite natural for SMMUv3. Yet, I recall Kevin said that VT-d
>>> doesn't want or need that.
>> Right, Intel currently doesn't need it, but I feel like everyone will
>> need this eventually as the fast invalidation path is quite important.
>>
> yes, there is no need but I don't see any harm of preparing for such
> extension on VT-d. Logically it's clearer, e.g. if we decide to move
> device TLB invalidation to a separate uAPI then vIOMMU is certainly
> a clearer object to carry it. and hardware extensions really looks like
> optimization on software implementations.
> 
> and we do need make a decision now, given if we make vIOMMU as
> a generic object for all vendors it may have potential impact on
> the user page fault support which Baolu is working on. the so-called
> fault object will be contained in vIOMMU, which is software managed
> on VT-d/SMMU but passed through on AMD. And probably we don't
> need another handle mechanism in the attach path, suppose the
> vIOMMU object already contains necessary information to find out
> iommufd_object for a reported fault.

Yes, if the vIOMMU object tracks all iommufd devices that it manages.

Best regards,
baolu