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Message-ID: <ZxvHGQJW65H+/zpy@Asurada-Nvidia>
Date: Fri, 25 Oct 2024 09:28:09 -0700
From: Nicolin Chen <nicolinc@...dia.com>
To: "Tian, Kevin" <kevin.tian@...el.com>
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Subject: Re: [PATCH v4 00/11] iommufd: Add vIOMMU infrastructure (Part-1)
On Fri, Oct 25, 2024 at 08:34:05AM +0000, Tian, Kevin wrote:
> > From: Nicolin Chen <nicolinc@...dia.com>
> > Sent: Tuesday, October 22, 2024 8:19 AM
> >
> > This series introduces a new vIOMMU infrastructure and related ioctls.
> >
> > IOMMUFD has been using the HWPT infrastructure for all cases, including a
> > nested IO page table support. Yet, there're limitations for an HWPT-based
> > structure to support some advanced HW-accelerated features, such as
> > CMDQV
> > on NVIDIA Grace, and HW-accelerated vIOMMU on AMD. Even for a multi-
> > IOMMU
> > environment, it is not straightforward for nested HWPTs to share the same
> > parent HWPT (stage-2 IO pagetable), with the HWPT infrastructure alone: a
> > parent HWPT typically hold one stage-2 IO pagetable and tag it with only
> > one ID in the cache entries. When sharing one large stage-2 IO pagetable
> > across physical IOMMU instances, that one ID may not always be available
> > across all the IOMMU instances. In other word, it's ideal for SW to have
> > a different container for the stage-2 IO pagetable so it can hold another
> > ID that's available.
>
> Just holding multiple IDs doesn't require a different container. This is
> just a side effect when vIOMMU will be required for other said reasons.
>
> If we have to put more words here I'd prefer to adding a bit more for
> CMDQV which is more compelling. not a big deal though. 😊
Ack.
> > For this "different container", add vIOMMU, an additional layer to hold
> > extra virtualization information:
> >
> > ________________________________________________________________
> > _______
> > | iommufd (with vIOMMU) |
> > | |
> > | [5] |
> > | _____________ |
> > | | | |
> > | |----------------| vIOMMU | |
> > | | | | |
> > | | | | |
> > | | [1] | | [4] [2] |
> > | | ______ | | _____________ ________ |
> > | | | | | [3] | | | | | |
> > | | | IOAS |<---|(HWPT_PAGING)|<---| HWPT_NESTED |<--| DEVICE | |
> > | | |______| |_____________| |_____________| |________| |
> > | | | | | | |
> >
> > |______|________|______________|__________________|_____________
> > __|_____|
> > | | | | |
> > ______v_____ | ______v_____ ______v_____ ___v__
> > | struct | | PFN | (paging) | | (nested) | |struct|
> > |iommu_device| |------>|iommu_domain|<----|iommu_domain|<----
> > |device|
> > |____________| storage|____________| |____________| |______|
> >
>
> nit - [1] ... [5] can be removed.
They are copied from the Documentation where numbers are needed.
I will take all the numbers out in the cover-letters.
> > The vIOMMU object should be seen as a slice of a physical IOMMU instance
> > that is passed to or shared with a VM. That can be some HW/SW resources:
> > - Security namespace for guest owned ID, e.g. guest-controlled cache tags
> > - Access to a sharable nesting parent pagetable across physical IOMMUs
> > - Virtualization of various platforms IDs, e.g. RIDs and others
> > - Delivery of paravirtualized invalidation
> > - Direct assigned invalidation queues
> > - Direct assigned interrupts
> > - Non-affiliated event reporting
>
> sorry no idea about 'non-affiliated event'. Can you elaborate?
I'll put an "e.g.".
> > On a multi-IOMMU system, the vIOMMU object must be instanced to the
> > number
> > of the physical IOMMUs that are passed to (via devices) a guest VM, while
>
> 'to the number of the physical IOMMUs that have a slice passed to ..."
Ack.
Thanks
Nicolin
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