On Sun, Jul 19, 2026 at 09:35:53AM +0100, Marc Zyngier wrote: > Mark Brown <[email protected]> wrote:
> > I've gone and implemented the first which will suppress the isb() for > > current host kernel SME usage, the second two are starting to get more > > fiddly than seems sensible to do right now. > I really wish you didn't optimise anything at all at this stage. > "Optimisation" is exactly what got us into so much trouble over the > past two years, and I really don't want SME in KVM to follow the same > trajectory. > So leave this is a straight ISB, no optimisation. Once you come back > with actual data showing that this is a terrible bottleneck affecting > real workloads on real HW, we'll look at it. But until then, please > keep it as stupid as possible. I've already left the KVM hypervisor code like that - I only updated the code here in the main kernel since that keeps the end effect for existing systems and workloads the same. I am aware that there has been a great deal of attention paid to the barriers we have in the context switch path so I am concerned that other people might have a different view on adding one.
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