Messages in this thread | | | From | "Huang, Kai" <> | Subject | Re: [PATCH v3 05/12] x86/tdx: Pass TDCALL/SEAMCALL input/output registers via a structure | Date | Thu, 27 Jul 2023 22:54:28 +0000 |
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On Thu, 2023-07-27 at 19:36 +0300, kirill.shutemov@linux.intel.com wrote: > On Wed, Jul 26, 2023 at 11:25:07PM +1200, Kai Huang wrote: > > diff --git a/arch/x86/virt/vmx/tdx/tdxcall.S b/arch/x86/virt/vmx/tdx/tdxcall.S > > index 6bdf6e137953..a0e7fe81bf63 100644 > > --- a/arch/x86/virt/vmx/tdx/tdxcall.S > > +++ b/arch/x86/virt/vmx/tdx/tdxcall.S > > @@ -17,34 +17,33 @@ > > * TDX module and hypercalls to the VMM. > > * SEAMCALL - used by TDX hosts to make requests to the > > * TDX module. > > + * > > + *------------------------------------------------------------------------- > > + * TDCALL/SEAMCALL ABI: > > + *------------------------------------------------------------------------- > > + * Input Registers: > > + * > > + * RAX - TDCALL/SEAMCALL Leaf number. > > + * RCX,RDX,R8-R9 - TDCALL/SEAMCALL Leaf specific input registers. > > + * > > + * Output Registers: > > + * > > + * RAX - TDCALL/SEAMCALL instruction error code. > > + * RCX,RDX,R8-R11 - TDCALL/SEAMCALL Leaf specific output registers. > > + * > > + *------------------------------------------------------------------------- > > So, you keep the existing asymetry in IN and OUT registers. R10 and R11 > are OUT-only registers. It can be confusing for user since it is the same > structure now. I guess it changes in the following patches, but I would > prefer to make them even here if there's no good reason not to. >
Do you mean you prefer to use R10/R11 as input too even in this patch?
I think _logically_ it should be part of the next patch, because w/o extending TDX_MODULE_CALL to support additional TDCALLs/SEAMCALLs, we don't need R10/R11 as input. This patch only changes to take a structure as function argument, rather than taking individual registers as argument.
Also, we have a comment to say this around the structure too:
/* - * Used in __tdx_module_call() to gather the output registers' values of the + * Used in __tdcall*() to gather the input/output registers' values of the * TDCALL instruction when requesting services from the TDX module. This is a * software only structure and not part of the TDX module/VMM ABI */ -struct tdx_module_output { +struct tdx_module_args { + /* input/output */ u64 rcx; u64 rdx; u64 r8; u64 r9; + /* additional output */ u64 r10; u64 r11; };
So to me there should be no confusion.
Even consider a theoretical case: someone wants to backport this patch to an old kernel w/o further patches, then it makes little sense to do R10/R11 in TDX_MODULE_CALL here in this patch
:-)
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