Date: Wed, 1 Oct 2003 12:41:56 +0100 From: Bruce M Simpson <bms@spc.org> To: Grumble <invalid@kma.eu.org> Cc: freebsd-questions@freebsd.org Subject: Re: Why is PCE not set in CR4? Message-ID: <20031001114155.GA12991@saboteur.dek.spc.org> In-Reply-To: <3F7AA0D8.1080801@kma.eu.org> References: <3F7AA0D8.1080801@kma.eu.org>
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On Wed, Oct 01, 2003 at 11:39:36AM +0200, Grumble wrote:
> >>However, I am not allowed to use the RDPMC instruction from ring 3
> >>because the PCE (Performance-monitoring Counters Enable) bit is not set.
> >
> >You can do it with /dev/perfmon. man 4 perfmon.
>
> I have read the perfmon documentation and source code. For several
> reasons, I do not think it is totally adequate in my situation.
[snip]
Hi,
Eat this. Diff attached. Test this and I'll commit it to -CURRENT if you're
happy with it. If you can tell me more about what perfmon needs I'll give
it love too.
This is an extension to the i386_vm86() syscall which will let you turn
PCE on and off if you're the superuser.
BMS
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Generated by diffcoll on Wed 1 Oct 2003 12:39:07 BST
diff -uN src/lib/libc/i386/sys/i386_vm86.2.orig src/lib/libc/i386/sys/i386_vm86.2
--- /usr/src/lib/libc/i386/sys/i386_vm86.2.orig Wed Oct 1 12:13:50 2003
+++ /usr/src/lib/libc/i386/sys/i386_vm86.2 Wed Oct 1 12:36:44 2003
@@ -112,6 +112,26 @@
.Fa state
will contain the state of the VME flag on return.
.\" .It Dv VM86_SET_VME
+.It Dv VM86_GET_PCE
+This is used to retrieve the current state of the Pentium(r) processor's
+PCE (Performance Counter Enable) flag, which is bit 8 of CR4.
+.Bd -literal
+struct vm86_pce_args {
+ int state; /* status */
+};
+.Ed
+.Pp
+.Fa state
+will contain the state of the VME flag on return.
+.It Dv VM86_SET_PCE
+This is used to set the current state of the PCE flag.
+Enabling this bit allows any code to execute the
+.Li RDPMC
+instruction.
+Disabling this bit will allow only code running at protection level 0 to
+execute this instruction.
+Because this bit has system-wide granularity, it may only be enabled by
+the superuser.
.El
.Pp
vm86 mode is entered by calling
@@ -133,6 +153,13 @@
.It Bq Er ENOMEM
There is not enough memory to initialize the kernel data structures.
.El
+.Sh BUGS
+The
+.Dv VM86_SETPCE
+and
+.Dv VM86_GETPCE
+functions are only guaranteed to work for uniprocessor kernels; their
+results on SMP systems are undefined.
.Sh AUTHORS
.An -nosplit
This man page was written by
diff -uN src/sys/i386/i386/vm86.c.orig src/sys/i386/i386/vm86.c
--- /usr/src/sys/i386/i386/vm86.c.orig Wed Oct 1 12:16:23 2003
+++ /usr/src/sys/i386/i386/vm86.c Wed Oct 1 12:39:01 2003
@@ -734,6 +734,29 @@
}
break;
+ case VM86_SET_PCE: {
+ struct vm86_pce_args sa;
+
+ if ((error = suser(td)))
+ return (error);
+ if (!(cpu_feature & CPUID_TSC) || !(cpu_feature & CPUID_MMX))
+ return (ENODEV);
+ if ((error = copyin(ua.sub_args, &sa, sizeof(sa))))
+ return (error);
+ if (sa.state)
+ load_cr4(rcr4() | CR4_PCE);
+ else
+ load_cr4(rcr4() & ~CR4_PCE);
+ }
+ break;
+
+ case VM86_GET_PCE: {
+ struct vm86_pce_args sa;
+
+ sa.state = (rcr4() & CR4_PCE ? 1 : 0);
+ error = copyout(&sa, ua.sub_args, sizeof(sa));
+ }
+
default:
error = EINVAL;
}
diff -uN src/sys/i386/include/vm86.h.orig src/sys/i386/include/vm86.h
--- /usr/src/sys/i386/include/vm86.h.orig Wed Oct 1 12:22:53 2003
+++ /usr/src/sys/i386/include/vm86.h Wed Oct 1 12:37:56 2003
@@ -128,6 +128,8 @@
#define VM86_SET_VME 2
#define VM86_GET_VME 3
#define VM86_INTCALL 4
+#define VM86_SET_PCE 5
+#define VM86_GET_PCE 6
struct vm86_init_args {
int debug; /* debug flag */
@@ -136,6 +138,10 @@
};
struct vm86_vme_args {
+ int state; /* status */
+};
+
+struct vm86_pce_args {
int state; /* status */
};
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