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 <redacted>
---
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,