[PATCHv2 1/4] x86/tdx: Introduce tdg_vm_wr()

[Kirill A. Shutemov]

Add a helper function to write to a TD-scope metadata field and use it
to set NOTIFY_ENABLES.

The helper function will be paired with tdg_vm_rd() and will be used to
manipulate other metadata fields, not just NOTIFY_ENABLES.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
---
 arch/x86/coco/tdx/tdx.c | 20 +++++++++++++++-----
 1 file changed, 15 insertions(+), 5 deletions(-)

diff --git a/arch/x86/coco/tdx/tdx.c b/arch/x86/coco/tdx/tdx.c
index 59776ce1c1d7..4fb36e5c4e80 100644
--- a/arch/x86/coco/tdx/tdx.c
+++ b/arch/x86/coco/tdx/tdx.c
@@ -77,6 +77,20 @@ static inline void tdcall(u64 fn, struct tdx_module_args *args)
 		panic("TDCALL %lld failed (Buggy TDX module!)\n", fn);
 }
 
+static inline u64 tdg_vm_wr(u64 field, u64 value, u64 mask)
+{
+	struct tdx_module_args args = {
+		.rdx = field,
+		.r8 = value,
+		.r9 = mask,
+	};
+
+	tdcall(TDG_VM_WR, &args);
+
+	/* Old value */
+	return args.r8;
+}
+
 /**
  * tdx_mcall_get_report0() - Wrapper to get TDREPORT0 (a.k.a. TDREPORT
  *                           subtype 0) using TDG.MR.REPORT TDCALL.
@@ -902,10 +916,6 @@ static void tdx_kexec_unshare_mem(void)
 
 void __init tdx_early_init(void)
 {
-	struct tdx_module_args args = {
-		.rdx = TDCS_NOTIFY_ENABLES,
-		.r9 = -1ULL,
-	};
 	u64 cc_mask;
 	u32 eax, sig[3];
 
@@ -924,7 +934,7 @@ void __init tdx_early_init(void)
 	cc_set_mask(cc_mask);
 
 	/* Kernel does not use NOTIFY_ENABLES and does not need random #VEs */
-	tdcall(TDG_VM_WR, &args);
+	tdg_vm_wr(TDCS_NOTIFY_ENABLES, 0, -1ULL);
 
 	/*
 	 * All bits above GPA width are reserved and kernel treats shared bit
-- 
2.43.0