commit e6a20ee66da70b356f7582ec6d074935ae27be86
Author: Dan Cross <cross@gajendra.net>
Date:   Thu Sep 23 13:42:22 2021 +0000

    Implement safe rdmsr for amd64
    
    Port the safe version of rdmsr to k10.
    
    Tested: Builds under plan9.
    
    Signed-off-by: Dan Cross <cross@gajendra.net>

diff --git a/sys/src/9k/k10/l64v.s b/sys/src/9k/k10/l64v.s
index 813ceb98b..73e61e7ff 100644
--- a/sys/src/9k/k10/l64v.s
+++ b/sys/src/9k/k10/l64v.s
@@ -175,11 +175,17 @@ TEXT rdtsc(SB), 1, $-4				/* Time Stamp Counter */
 
 TEXT rdmsr(SB), 1, $-4				/* Model-Specific Register */
 	MOVL	RARG, CX
+TEXT mayberdmsr(SB), 0, $-4
 	RDMSR
+_rdmsrret:
 	XCHGL	DX, AX				/* swap lo/hi, zero-extend */
 	SHLQ	$32, AX				/* hi<<32 */
 	ORQ	DX, AX				/* (hi<<32)|lo */
 	RET
+TEXT rdmsrfail(SB), 0, $-4
+	MOVL	$0xffffffff, AX
+	MOVL	AX, DX
+	JMP		_rdmsrret
 
 TEXT wrmsr(SB), 1, $-4
 	MOVL	RARG, CX
diff --git a/sys/src/9k/k10/trap.c b/sys/src/9k/k10/trap.c
index 772d17763..51c1e2627 100644
--- a/sys/src/9k/k10/trap.c
+++ b/sys/src/9k/k10/trap.c
@@ -15,6 +15,7 @@
 extern int notify(Ureg*);
 
 static void debugbpt(Ureg*, void*);
+static void faultgpf(Ureg*, void*);
 static void faultamd64(Ureg*, void*);
 static void doublefault(Ureg*, void*);
 static void unexpected(Ureg*, void*);
@@ -190,6 +191,7 @@ trapinit(void)
 	 * Syscall() is called directly without going through trap().
 	 */
 	trapenable(IdtBP, debugbpt, 0, "#BP");
+	trapenable(IdtGP, faultgpf, 0, "#GP");
 	trapenable(IdtPF, faultamd64, 0, "#PF");
 	trapenable(IdtDF, doublefault, 0, "#DF");
 	trapenable(Idt0F, unexpected, 0, "#15");
@@ -528,6 +530,17 @@ unexpected(Ureg* ureg, void*)
 	iprint("unexpected trap %llud; ignoring\n", ureg->type);
 }
 
+extern void mayberdmsr(void);
+extern void rdmsrfail(void);
+
+static void
+faultgpf(Ureg* ureg, void*)
+{
+	if(ureg->ip != (u64int)mayberdmsr)
+		panic("unhandled GPF at 0x%016llux", ureg->ip);
+	ureg->ip = (u64int)rdmsrfail;
+}
+
 static void
 faultamd64(Ureg* ureg, void*)
 {