add facility for poking and prodding x86 MSRs.

Reference: /n/atom/patch/applied/rdmsr
Date: Tue Apr  8 19:47:49 CES 2014
Signed-off-by: quanstro@quanstro.net

--- /sys/src/cmd/aux/rdmsr.c	Thu Jan  1 00:00:00 1970
+++ /sys/src/cmd/aux/rdmsr.c	Tue Apr  8 19:47:30 2014
@@ -0,0 +1,41 @@
+#include <u.h>
+#include <libc.h>
+
+void
+usage(void)
+{
+	fprint(2, "usage: rdmsr ...\n");
+	exits("usage");
+}
+
+void
+rdmsr(char *s)
+{
+	char buf[32];
+	int fd, n;
+	u32int msr;
+
+	msr = strtoul(s, 0, 0);
+	fd = open("/dev/msr", OREAD);
+	if(fd == -1)
+		sysfatal("%s: open: %r", argv0);
+	n = pread(fd, buf, sizeof buf, msr);
+	if(n > 0)
+		write(1, buf, n);
+	close(fd);
+}
+
+void
+main(int argc, char **argv)
+{
+	int i;
+
+	ARGBEGIN{
+	default:
+		usage();
+	}ARGEND
+
+	for(i = 0; i < argc; i++)
+		rdmsr(argv[i]);
+	exits("");
+}
--- /sys/src/cmd/aux/wrmsr.c	Thu Jan  1 00:00:00 1970
+++ /sys/src/cmd/aux/wrmsr.c	Tue Apr  8 19:47:30 2014
@@ -0,0 +1,39 @@
+#include <u.h>
+#include <libc.h>
+
+void
+usage(void)
+{
+	fprint(2, "usage: %s msr value ...\n", argv0);
+	exits("usage");
+}
+
+void
+rdmsr(char *s, char *v)
+{
+	int fd;
+
+	fd = open("/dev/msr", OREAD);
+	if(fd == -1)
+		sysfatal("%s: open: %r", argv0);
+	if(pwrite(fd, v, strlen(v), strtoul(s, 0, 0)) == -1)
+		sysfatal("%s: pwrite: %r", argv0);
+	close(fd);
+}
+
+void
+main(int argc, char **argv)
+{
+	int i;
+
+	ARGBEGIN{
+	default:
+		usage();
+	}ARGEND
+	if(argc & 1)
+		usage();
+
+	for(i = 0; i < argc; i += 2)
+		rdmsr(argv[i], argv[i+1]);
+	exits("");
+}
--- /sys/src/cmd/aux/mkfile	Tue Apr  8 19:47:30 2014
+++ /sys/src/cmd/aux/mkfile	Tue Apr  8 19:47:30 2014
@@ -30,6 +30,7 @@
 	olefs\
 	pcmcia\
 	portmap\
+	rdmsr\
 	rdwr\
 	reboot\
 	searchfs\
@@ -39,6 +40,7 @@
 	trampoline\
 	usage\
 	write\
+	wrmsr\
 	xlisten\
 	zerotrunc\
 
--- /sys/src/nix/k10/devarch.c	Tue Apr  8 19:47:30 2014
+++ /sys/src/nix/k10/devarch.c	Tue Apr  8 19:47:30 2014
@@ -399,11 +399,45 @@
 	return readstr(off, a, n, buf);
 }
 
+/* need to catch #GP */
+static long
+msrread(Chan*, void *a, long n, vlong o)
+{
+	char buf[32];
+	u32int msr;
+	uvlong v;
+
+	if(o != (uint)o)
+		error(Egreg);
+	msr = (uint)o;
+	v = rdmsr(msr);
+	snprint(buf, sizeof buf, "%#.16llux\n", v);
+	return readstr(0, a, n, buf);
+}
+
+static long
+msrwrite(Chan*, void *a, long n, vlong o)
+{
+	char buf[32];
+	u32int msr;
+	uvlong v;
+
+	if(o != (uint)o || n > 31)
+		error(Egreg);
+	memmove(buf, a, n);
+	buf[n] = 0;
+	v = strtoull(buf, nil, 0);
+	msr = (uint)o;
+	wrmsr(msr, v);
+	return n;
+}
+
 void
 archinit(void)
 {
 	addarchfile("cputype", 0444, cputyperead, nil);
 	addarchfile("archcfg", 0444, archcfgread, nil);
+	addarchfile("msr", 0664, msrread, msrwrite);
 }
 
 void
--- /sys/man/8/rdmsr	Thu Jan  1 00:00:00 1970
+++ /sys/man/8/rdmsr	Tue Apr  8 19:47:30 2014
@@ -0,0 +1,25 @@
+.TH RDMSR 8
+.SH NAME
+rdmsr, wrmsr \- read and write x86 model specific registers
+.SH SYNOPSIS
+.B aux/rdmsr
+.I msr
+...
+.br
+.B aux/wrmsr
+.I msr
+.I value
+...
+.SH DESCRIPTION
+These programs allow direct access to x86 model specific
+registers.  Since MSRs may not be read by user programs,
+they require
+.BR /dev/msr .
+.SH SOURCE
+.B /sys/src/cmd/aux/rdmsr.c
+.br
+.B /sys/src/cmd/aux/wrmsr.c
+.SH BUGS
+Invalid MSR references may result in a #GP trap and
+crash.
+