On Thu, Jul 13, 2023 at 08:18:09AM +0000, Huang, Kai wrote: > On Thu, 2023-07-13 at 09:42 +0200, Peter Zijlstra wrote: > > On Thu, Jul 13, 2023 at 03:46:52AM +0000, Huang, Kai wrote: > > > On Wed, 2023-07-12 at 15:15 -0700, Isaku Yamahata wrote: > > > > > The SEAMCALL ABI is very similar to the TDCALL ABI and leverages much > > > > > TDCALL infrastructure. Wire up basic functions to make SEAMCALLs for > > > > > the basic TDX support: __seamcall(), __seamcall_ret() and > > > > > __seamcall_saved_ret() which is for TDH.VP.ENTER leaf function. > > > > > > > > Hi. __seamcall_saved_ret() uses struct tdx_module_arg as input and output. For > > > > KVM TDH.VP.ENTER case, those arguments are already in unsigned long > > > > kvm_vcpu_arch::regs[]. It's silly to move those values twice. From > > > > kvm_vcpu_arch::regs to tdx_module_args. From tdx_module_args to real registers. > > > > > > > > If TDH.VP.ENTER is the only user of __seamcall_saved_ret(), can we make it to > > > > take unsigned long kvm_vcpu_argh::regs[NR_VCPU_REGS]? Maybe I can make the > > > > change with TDX KVM patch series. > > > > > > The assembly code assumes the second argument is a pointer to 'struct > > > tdx_module_args'. I don't know how can we change __seamcall_saved_ret() to > > > achieve what you said. We might change the kvm_vcpu_argh::regs[NR_VCPU_REGS] to > > > match 'struct tdx_module_args''s layout and manually convert part of "regs" to > > > the structure and pass to __seamcall_saved_ret(), but it's too hacky I suppose. > > > > I suspect the kvm_vcpu_arch::regs layout is given by hardware; so the > > only option would be to make tdx_module_args match that. It's a slightly > > unfortunate layout, but meh. > > > > Then you can simply do: > > > > __seamcall_saved_ret(leaf, (struct tdx_module_args *)vcpu->arch->regs); > > > > > > I don't think the layout matches hardware, especially I think there's no > "hardware layout" for GPRs that are concerned here. They are just for KVM > itself to save guest's registers when the guest exits to KVM, so that KVM can > restore them when returning back to the guest. Either way around it should be possible to make them match I suppose. Ideally we get the callee-clobbered regs first, but if not, I don't think that's too big of a problem.
