Re: [PATCH v4 1/2] iommu/sva: Tighten SVA bind API with explicit flags

[Luck, Tony]

On Thu, May 13, 2021 at 12:46:21PM -0700, Jacob Pan wrote:
> It seems there are two options:
> 1. Add a new IOMMU API to set up a system PASID with a *separate* IOMMU page
> table/domain, mark the device is PASID only with a flag. Use DMA APIs
> to explicit map/unmap. Based on this PASID-only flag, Vendor IOMMU driver
> will decide whether to use system PASID domain during map/unmap. Not clear
> if we also need to make IOVA==kernel VA.
> 
> 2. Add a new IOMMU API to setup a system PASID which points to init_mm.pgd.
> This API only allows trusted device to bind with the system PASID at its
> own risk. There is no need for DMA API. This is the same as the current
> code except with an explicit API.
> 
> Which option?

Option #1 looks cleaner to me. Option #2 gives access to bits
of memory that the users of system PASID shouldn't ever need
to touch ... just map regions of memory that the kernel has
a "struct page" for.

What does "use DMA APIs to explicitly map/unmap" mean? Is that
for the whole region?

I'm expecting that once this system PASID has been initialized,
then any accelerator device with a kernel use case would use the
same PASID. I.e. DSA for page clearing, IAX for ZSwap compression
& decompression, etc.

-Tony