Re: [PATCH v3 12/12] x86/virt/tdx: Adjust 'struct tdx_module_args' to use x86 "register index" layout

From: kirill . shutemov
Date: Sun Aug 06 2023 - 07:50:39 EST

On Wed, Jul 26, 2023 at 11:25:14PM +1200, Kai Huang wrote:
> For TDX guest, KVM needs to call __seamcall_saved_ret() to make the
> TDH.VP.ENTER SEAMCALL to enter the guest, possibly taking all registers
> in 'struct tdx_module_args' as input/output.
> KVM caches guest's GPRs in 'kvm_vcpu_arch::regs[]', which follows the
> "register index" hardware layout of x86 GPRs. On the other hand, the
> __seamcall_saved_ret() takes the pointer of 'struct tdx_module_args' as
> argument, thus there's a mismatch.
> KVM could choose to copy input registers from 'vcpu::regs[]' to a
> 'struct tdx_module_args' and use that as argument to make the SEAMCALL,
> but such memory copy isn't desired and should be avoided if possible.

I doubt the copy will be visible on any profile.

I personally don't like that kvm implementation detail leaks here. It
suppose to be generic TDX code.

Kiryl Shutsemau / Kirill A. Shutemov