On Mon, Jan 09, 2017 at 12:26:39PM +0000, Russell King - ARM Linux wrote: > On Tue, Jan 03, 2017 at 10:51:49AM +0100, Christoffer Dall wrote: > > Hi Russell, > > > > On Thu, Dec 15, 2016 at 06:57:18PM +0000, Russell King - ARM Linux wrote: > > > What's also coming clear is that there's very few people who understand > > > all the interactions here, and the whole thing seems to be an undocumented > > > mess. > > > > I think the hyp stub has just served a very limited purpose so far, and > > therefore is a somewhat immature implementation. Now we've discovered a > > need to clean it up, and we're all for that. Again, I don't think the > > problem is any larger than that, we just need to fix it, and it seems to > > me everyone is willing to work on that. > > What I want to see is some documentation of the hyp-stub, so that there > can be some element of confidence that changes there are properly > coordinated. As I said in a follow up email: > > | Either we need more people to have an understanding (so if one of them > | gets run over by a bus, we're not left floundering around) or we need > | it to be documented - even if it's just a simple comment "the ABI in > | this file is shared with XYZ, if you change the ABI here, also update > | XYZ too." > > > Marc even offered to work on your suggestion to support the general > > hyp ABI commands in KVM. > > ... which is pointless, because it's a duplication of the effort I've > already put in. My patches already do the: > > #define HVC_GET_VECTORS 0 > #define HVC_SET_VECTORS 1 > #define HVC_SOFT_RESTART 2 > > thing which ARM64 does, passing the arguments in via the appropriate > registers. However, such a change is a major revision of hyp-stub's > ABI, which completely changes the way it works. Sorry, I'm afraid I might have been unclear. What I meant with "general hyp ABI commands in KVM" was, that if there's a need for KVM to support the operations (using a unified and documented ABI) that the hyp stub supports, then we could add that in KVM as well. I thought your patches added the functionality for the hyp stub, and Marc would add whichever remaining pieces in the KVM side. [...] > > Longer term, I'd like to see the existing hypervisor documentation in > Documentation/virtual/kvm/hypercalls.txt updated with the ARM details. > According to that document, KVM effectively only exists on PPC and x86 > at the present time... > I'm afraid I don't think this is right place to document this behavior. There's a difference between an internal ABI between code running in two CPU modes but both part of the same kernel, and a hypervisor running a guest OS on top. I believe that Documentation/virtual/kvm/hypercalls.txt documents the latter case (i.e. guest hypercalls supported by the KVM host hypervisor), not the former case, and these things should not be combined. I would suggest adding something like Documentation/virtual/kvm/arm/hyp-abi.txt instead. -Christoffer _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
