On Wed, 2023-09-13 at 15:15 +0000, Sean Christopherson wrote: > > > e.g. if userspace writes '0' immediately after creating, and then later writes a > > > small delta, the v6 code wouldn't trigger synchronization because "user_set_tsc" > > > would be left unseft by the write of '0'. > > > > True, but that's the existing behaviour, > > No? The existing code will fall into the "conditionally sync" logic for any > non-zero value. Yeah, OK. This isn't one of the cases we set out to deliberately change, but it would be changed by v6 of the patch, and I suppose you're right that we should accept a small amount of extra code complexity just to avoid making any changes we don't *need* to, even for stupid cases like this. > I don't care (in the Tommy Lee Jones[*] sense). All I care about is minimizing > the probability of breaking userspace, which means making the smallest possible > change to KVM's ABI. For me, whether or not userspace is doing something sensible > doesn't factor into that equation. Ack. Although there's a strong argument that adding further warts to an already fundamentally broken API probably isn't a great idea in the first place. Just deprecate it and use the saner replacement API... which I just realised we don't have (qv). Ooops :)
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