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 RQ6vgmVE 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 29/1/26 12:16, Jason Gunthorpe wrote: > On Wed, Jan 28, 2026 at 05:03:27PM -0800, Sean Christopherson wrote: > >> For a dmabuf fd, the story is the same as guest_memfd. Unless private vs. shared >> is all or nothing, and can never change, then the only entity that can track that >> info is the owner of the dmabuf. And even if the private vs. shared attributes >> are constant, tracking it external to KVM makes sense, because then the provider >> can simply hardcode %true/%false. > > Oh my I had not given that bit any thought. My remarks were just about > normal non-CC systems. > > So MMIO starts out shared, and then converts to private when the guest > triggers it. It is not all or nothing, there are permanent shared > holes in the MMIO ranges too. > > Beyond that I don't know what people are thinking. > > Clearly VFIO has to revoke and disable the DMABUF once any of it > becomes private. huh? Private MMIO still has to be mapped in the NPT (well, on AMD). It is the userspace mapping which we do not want^wneed and we do not by using dmabuf. > VFIO will somehow have to know when it changes modes > from the TSM subsystem. > > I guess we could have a special channel for KVM to learn the > shared/private page by page from VFIO as some kind of "aware of CC" > importer. Yilun is doing something like that in (there must be a newer version somewhere) https://lore.kernel.org/all/20250529053513.1592088-1-yilun.xu@linux.intel.com/ > I suppose AMD needs to mangle the RMP when it changes, and KVM has to > do that. True. > I forget what ARM does, but I seem to recall there is a call to create > a vPCI function and that is what stuffs the S2? So maybe KVM isn't > even involved? (IIRC people were talking that something else would > call the vPCI function but I haven't seen patches) > > No idea what x86 does beyond it has to unmap all the MMIO otherwise > the machine crashes :P When it is in the hypervisor area, there is no "x86" :) The "AMD x86" does not crash if there are mappings which won't work, it faults/fences when these are accessed. > Oh man, what a horrible mess to even contemplate. I'm going to bed. > > > Jason -- Alexey