RE: [PATCH V8.1 5/9] x86/sev-es: Expose sev_es_ghcb_hv_call() to call ghcb hv call out of sev code

[Michael Kelley <mikelley@microsoft.com>]

From: Tianyu Lan <ltykernel@gmail.com> Sent: Friday, October 22, 2021 6:37 AM
> 
> Hyper-V needs to call ghcb hv call to write/read MSR in Isolation VM.
> So expose sev_es_ghcb_hv_call() to call it in the Hyper-V code.
> 
> Hyper-V Isolation VM is unenlightened guests and run a paravisor in the
> VMPL0 for communicating and GHCB pages are being allocated and set up by
> that paravisor. Linux gets ghcb page pa via MSR_AMD64_SEV_ES_GHCB
> from paravisor and should not change it. Add set_ghcb_msr parameter for
> sev_es_ghcb_hv_call() and not set ghcb page pa when it's false.
> 
> Signed-off-by: Tianyu Lan <Tianyu.Lan@microsoft.com>
> ---
> Change since v8:
>         Fix commit in the sev_es_ghcb_hv_call().
> 
>  arch/x86/include/asm/sev.h   | 12 ++++++++++++
>  arch/x86/kernel/sev-shared.c | 25 ++++++++++++++++---------
>  arch/x86/kernel/sev.c        | 13 +++++++------
>  3 files changed, 35 insertions(+), 15 deletions(-)
> 
> diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h
> index fa5cd05d3b5b..5b7f7e2b81f7 100644
> --- a/arch/x86/include/asm/sev.h
> +++ b/arch/x86/include/asm/sev.h
> @@ -81,12 +81,24 @@ static __always_inline void sev_es_nmi_complete(void)
>  		__sev_es_nmi_complete();
>  }
>  extern int __init sev_es_efi_map_ghcbs(pgd_t *pgd);
> +extern enum es_result sev_es_ghcb_hv_call(struct ghcb *ghcb,
> +					  bool set_ghcb_msr,
> +					  struct es_em_ctxt *ctxt,
> +					  u64 exit_code, u64 exit_info_1,
> +					  u64 exit_info_2);
>  #else
>  static inline void sev_es_ist_enter(struct pt_regs *regs) { }
>  static inline void sev_es_ist_exit(void) { }
>  static inline int sev_es_setup_ap_jump_table(struct real_mode_header *rmh) { return 0; }
>  static inline void sev_es_nmi_complete(void) { }
>  static inline int sev_es_efi_map_ghcbs(pgd_t *pgd) { return 0; }
> +static inline enum
> +es_result sev_es_ghcb_hv_call(struct ghcb *ghcb,
> +			      bool set_ghcb_msr, u64 exit_code,

The "struct es_em_ctxt *ctxt" argument is missing from this declaration,
which would presumably produce a compile error.

> +			      u64 exit_info_1, u64 exit_info_2)
> +{
> +	return ES_VMM_ERROR;
> +}
>  #endif
> 
>  #endif