On Mon, 2026-10-12 at 09:58 +0000, Fred Griffoul wrote: > > I plan to change the revoke anyway, because iommufd must not leave the > device with a hole: it should replace mappings in place instead of > unmapping and remapping. Would that fit your case? I suspect it depends > on locking, for example whether you have to revoke while holding > memory_lock.
I was keeping that hack *entirely* separate from the guest_memfd work. That's a quirk on the IOAS in iommufd: "whenever you unmap, put *this* page in its place instead". It doesn't belong anywhere near what we're doing here, ideally. I even talked to Jason about it about it at LPC, and he didn't hurt me. If we implement a hitless¹ REPLACE operation then the scratch-page ends up being a fairly trivial thing to redirect UNMAP to REPLACE (the tricksy detail being that it uses the *same* scratch page for every IOVA in the range). ¹ why do we call it that? Shouldn't it be 'missless'?
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