Hi Will, On Mon, Sep 14, 2020 at 06:40:09PM +0100, Will Deacon wrote: > Hi David, > > On Thu, Sep 03, 2020 at 11:17:02AM +0200, David Brazdil wrote: > > Introduce '.hyp.data..percpu' as part of ongoing effort to make nVHE > > hyp code self-contained and independent of the rest of the kernel. > > > > The series builds on top of the "Split off nVHE hyp code" series which > > used objcopy to rename '.text' to '.hyp.text' and prefix all ELF > > symbols with '__kvm_nvhe' for all object files under kvm/hyp/nvhe. > > I've been playing around with this series this afternoon, trying to see > if we can reduce the coupling between the nVHE code and the core code. I've > ended up with the diff below on top of your series, but I think it actually > removes the need to change the core code at all. The idea is to collapse > the percpu sections during prelink, and then we can just deal with the > resulting data section a bit like we do for .hyp.text already. > > Have I missed something critical? I was wondering whether this approach would be sufficient as well because of the simplicity. We'd just need to be careful about correctly preserving the semantics of the different .data..percpu..* sections. For instance, I've noticed you make .hyp..data..percpu page-aligned rather than cacheline-aligned. We need that for stage-2 unmapping but it also happens to correctly align DEFINE_PER_CPU_PAGE_ALIGNED variables when collapsed into the single hyp section. The reason why I ended up reusing the global macro was to avoid introducing subtleties like that into the arm64 linker script. Do you think it's a worthwhile trade off? One place where this approach doesn't work is DEFINE_PER_CPU_FIRST. But I'm guessing that's something we can live without. I was also wondering about another approach - using the PERCPU_SECTION macro unchanged in the hyp linker script. It would lay out a single .data..percpu and we would then prefix it with .hyp and the symbols with __kvm_nvhe_ as with everything else. WDYT? Haven't tried that yet, could be a naive idea. Thanks for reviewing, David
