On Mon, Jan 09, 2017 at 02:05:00PM +0000, Russell King - ARM Linux wrote: > So, although Marc produced a patch which updates the KVM hypervisor for > the GET_VECTORS change, through reading the code today, it's become clear > that much more is needed, so I'm yet again banging on about documentation. > It's only become clear to me today that the KVM stub calling convention > for the host kernel is: > > entry: > r0 = function pointer > r1 = 32-bit function argument 0 > r2 = 32-bit function argument 1 > r3 = 32-bit function argument 2 > no further arguments are supported > --- or --- > r0 = -1 (or 0 post Marc's patch) for get_vectors > exit: > r0 = vectors (if get_vectors call was made) > otherwise, who knows... > > I specify "32-bit" there because they're shifted by one register, which, > if a 64-bit argument is passed with EABI, the arguments will no longer be > appropriately aligned... so it's an important detail to be aware of with > the current KVM hypervisor interface. > > What I want to do here is to fix this kexec issue completely, not in a > piecemeal fashion - I'm not interested in fixing one small problem, then > coming back to it in a few months time to fix another problem. That's a > waste of time (well, unless you're into job creation.) I've always been > for "if you're going to do the job, damn well do the job properly". So > I'm not going to accept anything short of fixing _both_ kexec and kdump > together. > > So, given that the hyp-stub has this ABI after my patches: > > entry: > r0 = argument (0 = get vectors, 1 = set vectors, 2 = call function) > r1 = vectors for r0 = 1 > r3 = function pointer (with bit 0 already set for thumb functions) > for r0 = 2 > exit: > r0 = -1 for invalid calls > r0 = current vectors address (for r0 = 0 on entry) > is not expected to return for r0 = 2 on entry > otherwise registers preserved preserved > > which is clearly incompatible with the current KVM stub, can we come up > with a common ABI that is satisfactory to both. > > The above are probably the very first time anyone has written out the > ABI of these things, and as can be seen, it's still something of a mess. For completeness, this is the existing hyp-stub ABI: entry: r0 = -1 => get_vectors r0 != -1 => set_vectors (to the value in r0) exit: r0 = current vector address And that's it. -- RMK's Patch system: http://www.armlinux.org.uk/developer/patches/ FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up according to speedtest.net. _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
