Messages in this thread Patch in this message | | | Date | Thu, 3 Aug 2023 13:58:10 +0300 | From | "" <> | Subject | Re: [PATCH v3 05/12] x86/tdx: Pass TDCALL/SEAMCALL input/output registers via a structure |
| |
On Thu, Jul 27, 2023 at 10:54:28PM +0000, Huang, Kai wrote: > 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?
Yes.
> 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.
As a user, if I see a struct used for in and out, I would expect that all fields have the same rules.
> 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.
Do you always read documentation? :P Maybe it is only me...
> 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 > > :-)
Consider the case whe the patch was (wrongly) backported to use new call that uses R10 as input.
I realize that all my objections are rather hand-wavy. I would like to have in/out symmetry here. But I would not NAK patch over this.
-- Kiryl Shutsemau / Kirill A. Shutemov
| |