change otg to host mode

hc

2024-05-11 04dd17822334871b23ea2862f7798fb0e0007777

 kernel/arch/x86/include/asm/debugreg.h
..
..
@@ -39,7 +39,20 @@
39
39
 		asm("mov %%db6, %0" :"=r" (val));
40
40
 		break;
41
41
 	case 7:
42
-		asm("mov %%db7, %0" :"=r" (val));
42
+		/*
43
+		 * Apply __FORCE_ORDER to DR7 reads to forbid re-ordering them
44
+		 * with other code.
45
+		 *
46
+		 * This is needed because a DR7 access can cause a #VC exception
47
+		 * when running under SEV-ES. Taking a #VC exception is not a
48
+		 * safe thing to do just anywhere in the entry code and
49
+		 * re-ordering might place the access into an unsafe location.
50
+		 *
51
+		 * This happened in the NMI handler, where the DR7 read was
52
+		 * re-ordered to happen before the call to sev_es_ist_enter(),
53
+		 * causing stack recursion.
54
+		 */
55
+		asm volatile("mov %%db7, %0" : "=r" (val) : __FORCE_ORDER);
43
56
 		break;
44
57
 	default:
45
58
 		BUG();
..
..
@@ -66,7 +79,16 @@
66
79
 		asm("mov %0, %%db6"	::"r" (value));
67
80
 		break;
68
81
 	case 7:
69
-		asm("mov %0, %%db7"	::"r" (value));
82
+		/*
83
+		 * Apply __FORCE_ORDER to DR7 writes to forbid re-ordering them
84
+		 * with other code.
85
+		 *
86
+		 * While is didn't happen with a DR7 write (see the DR7 read
87
+		 * comment above which explains where it happened), add the
88
+		 * __FORCE_ORDER here too to avoid similar problems in the
89
+		 * future.
90
+		 */
91
+		asm volatile("mov %0, %%db7"	::"r" (value), __FORCE_ORDER);
70
92
 		break;
71
93
 	default:
72
94
 		BUG();