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, 3 Aug 2023 11:35:48 +0000 |
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On Thu, 2023-08-03 at 13:58 +0300, kirill.shutemov@linux.intel.com wrote: > 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. >
The only concern is I don't particularly like to add additional logic to this patch. Anyway not big deal to me. I can do what you said if I don't see Peter's (or other maintainers') comment on this.
Btw, should I say something like below in the changelog to justify this additional logic:
Also use R10/R11 as input registers too to make the input/output registers symmetric, although currently no TDCALL/SEAMCALL use them as input registers.
?
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