[PATCH 2/4] x86/tdx: Use ReportFatalError to report missing SEPT_VE_DISABLE

[Kirill A. Shutemov]

The check for SEPT_VE_DISABLE happens early in the kernel boot where
earlyprintk is not yet functional. Kernel successfully detect broken
TD configuration and stops the kernel with panic(), but it cannot
communicate the reason to the user.

Use TDG.VP.VMCALL<ReportFatalError> to report the error. The hypercall
can encode message up to 64 bytes in eight registers.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
---
 arch/x86/coco/tdx/tdx.c | 38 +++++++++++++++++++++++++++++++++++++-
 1 file changed, 37 insertions(+), 1 deletion(-)

diff --git a/arch/x86/coco/tdx/tdx.c b/arch/x86/coco/tdx/tdx.c
index cfd4c95b9f04..8ad04d101270 100644
--- a/arch/x86/coco/tdx/tdx.c
+++ b/arch/x86/coco/tdx/tdx.c
@@ -22,6 +22,7 @@
 
 /* TDX hypercall Leaf IDs */
 #define TDVMCALL_MAP_GPA		0x10001
+#define TDVMCALL_REPORT_FATAL_ERROR	0x10003
 
 /* MMIO direction */
 #define EPT_READ	0
@@ -140,6 +141,41 @@ int tdx_mcall_get_report0(u8 *reportdata, u8 *tdreport)
 }
 EXPORT_SYMBOL_GPL(tdx_mcall_get_report0);
 
+static void __noreturn tdx_panic(const char *msg)
+{
+	struct tdx_hypercall_args args = {
+		.r10 = TDX_HYPERCALL_STANDARD,
+		.r11 = TDVMCALL_REPORT_FATAL_ERROR,
+		.r12 = 0, /* Error code: 0 is Panic */
+	};
+	union {
+		/* Define register order according to the GHCI */
+		struct { u64 r14, r15, rbx, rdi, rsi, r8, r9, rdx; };
+
+		char str[64];
+	} message;
+
+	/* VMM assumes '\0' in byte 65, if the message took all 64 bytes */
+	strncpy(message.str, msg, 64);
+
+	args.r8  = message.r8;
+	args.r9  = message.r9;
+	args.r14 = message.r14;
+	args.r15 = message.r15;
+	args.rdi = message.rdi;
+	args.rsi = message.rsi;
+	args.rbx = message.rbx;
+	args.rdx = message.rdx;
+
+	/*
+	 * Keep calling the hypercall in case VMM did not terminated
+	 * the TD as it must.
+	 */
+	while (1) {
+		__tdx_hypercall(&args, 0);
+	}
+}
+
 static void tdx_parse_tdinfo(u64 *cc_mask)
 {
 	struct tdx_module_output out;
@@ -172,7 +208,7 @@ static void tdx_parse_tdinfo(u64 *cc_mask)
 	 */
 	td_attr = out.rdx;
 	if (!(td_attr & ATTR_SEPT_VE_DISABLE))
-		panic("TD misconfiguration: SEPT_VE_DISABLE attibute must be set.\n");
+		tdx_panic("TD misconfiguration: SEPT_VE_DISABLE attribute must be set.");
 }
 
 /*
-- 
2.38.0