Re: [PATCH 09/10] x86/virt/tdx: Wire up basic SEAMCALL functions

[Peter Zijlstra]

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);