On Fri, Apr 08, 2022 at 08:05:38AM +0000, Tian, Kevin wrote: > > From: Jason Gunthorpe <jgg@xxxxxxxxxx> > > Sent: Thursday, April 7, 2022 11:24 PM > > > > This new mechanism will replace using IOMMU_CAP_CACHE_COHERENCY > > and > > IOMMU_CACHE to control the no-snoop blocking behavior of the IOMMU. > > > > Currently only Intel and AMD IOMMUs are known to support this > > feature. They both implement it as an IOPTE bit, that when set, will cause > > PCIe TLPs to that IOVA with the no-snoop bit set to be treated as though > > the no-snoop bit was clear. > > > > The new API is triggered by calling enforce_cache_coherency() before > > mapping any IOVA to the domain which globally switches on no-snoop > > blocking. This allows other implementations that might block no-snoop > > globally and outside the IOPTE - AMD also documents such a HW capability. > > > > Leave AMD out of sync with Intel and have it block no-snoop even for > > in-kernel users. This can be trivially resolved in a follow up patch. > > > > Only VFIO will call this new API. > > I still didn't see the point of mandating a caller for a new API (and as > you pointed out iommufd will call it too). The language is not to mandate, but to explain why this hasn't come with a core iommu wrapper function to call it. > it reads like no_snoop is the result of the enforcement... Probably > force_snooping better matches the intention here. Done Thanks, Jason
