On 27.02.2023 13:06, Andrew Cooper wrote: > On 27/02/2023 11:33 am, Jan Beulich wrote: >> On 27.02.2023 12:15, Andrew Cooper wrote: >>> On 27/02/2023 10:46 am, Jan Beulich wrote: >>>> On 24.02.2023 22:33, Andrew Cooper wrote: >>>>> But I think we want to change tact slightly at this point, so I'm not >>>>> going to do any further tweaking on commit. >>>>> >>>>> Next, I think we want to rename asm/hvm/svm/svm.h to asm/hvm/svm.h, >>>>> updating the non-SVM include paths as we go. Probably best to >>>>> chain-include the other svm/hvm/svm/*.h headers temporarily, so we've >>>>> only got one tree-wide cleanup of the external include paths. >>>>> >>>>> Quick tangent - I will be making all of that cpu_has_svm_* >>>>> infrastructure disappear by moving it into the normal CPUID handling, >>>>> but I've not had sufficient time to finish that yet. >>>>> >>>>> Next, hvm/svm/nestedsvm.h can merge straight into hvm/svm.h, and >>>>> disappear (after my decoupling patch has gone in). >>>> Why would you want to fold hvm/svm/nestedsvm.h into hvm/svm/svm.h? >>>> The latter doesn't use anything from the former, does it? >>> It's about what else uses them. >>> >>> hvm_vcpu needs both svm_vcpu and nestedsvm, so both headers are always >>> included in tandem. >> Well, yes, that's how things are today. But can you explain to me why >> hvm_vcpu has to know nestedsvm's layout? > > Because it's part of the same single memory allocation.
Which keeps growing, and sooner or later we'll need to find something again to split off, so we won't exceed a page in size. The nested structures would, to me, look to be prime candidates for such. >> If the field was a pointer, >> a forward decl of that struct would suffice, and any entity in the >> rest of Xen not caring about struct nestedsvm would no longer see it >> (and hence also no longer be re-built if a change is made there). > > Yes, you could hide it as a pointer. The cost of doing so is an > unnecessary extra memory allocation, and extra pointer handling on > create/destroy, not to mention extra pointer chasing in memory during use. > >>> nestedsvm is literally just one struct now, and no subsystem ought to >>> have multiple headers when one will do. >> When one will do, yes. Removing build dependencies is a good reason >> to have separate headers, though. > > Its not the only only option, and an #ifdef CONFIG_NESTED_VIRT inside > the struct would be an equally acceptable way of doing this which > wouldn't involve making an extra memory allocation. That would make it a build-time decision, but then on NESTED_VIRT=y hypervisors there might still be guests not meaning to use that functionality, and for quite some time that may actually be a majority. > Everything you've posed here is way out of scope for Xenia's series. There was never an intention to extend the scope of the work she's doing. Instead I was trying to limit the scope by suggesting to avoid a piece of rework which later may want undoing. Jan
