On Wed, 2023-07-12 at 19:11 +0200, Peter Zijlstra wrote: > On Wed, Jul 12, 2023 at 08:55:21PM +1200, Kai Huang wrote: > > @@ -65,6 +104,37 @@ > > .endif > > > > .if \ret > > + .if \saved > > + /* > > + * Restore the structure from stack to saved the output registers > > + * > > + * In case of VP.ENTER returns due to TDVMCALL, all registers are > > + * valid thus no register can be used as spare to restore the > > + * structure from the stack (see "TDH.VP.ENTER Output Operands > > + * Definition on TDCALL(TDG.VP.VMCALL) Following a TD Entry"). > > + * For this case, need to make one register as spare by saving it > > + * to the stack and then manually load the structure pointer to > > + * the spare register. > > + * > > + * Note for other TDCALLs/SEAMCALLs there are spare registers > > + * thus no need for such hack but just use this for all for now. > > + */ > > + pushq %rax /* save the TDCALL/SEAMCALL return code */ > > + movq 8(%rsp), %rax /* restore the structure pointer */ > > + movq %rsi, TDX_MODULE_rsi(%rax) /* save %rsi */ > > + movq %rax, %rsi /* use %rsi as structure pointer */ > > + popq %rax /* restore the return code */ > > + popq %rsi /* pop the structure pointer */ > > Urgghh... At least for the \host case you can simply pop %rsi, no? > VP.ENTER returns with 0 there IIRC. No VP.ENTER doesn't return 0 for RAX. Firstly, VP.ENTER can return for many reasons but not limited to TDVMCALL (e.g., due to interrupt), and for those cases RAX contains valid non-zero value. Secondly, even for TDVMCALL, the RAX isn't 0: Table 6.256 TDX 1.5 ABI spec: RAX SEAMCALL instruction return code The DETAILS_L2 field in bits 31:0 contain the VMCS exit reason, indicating TDCALL (77).
