svn commit: r186252 - head/sys/kern

[Ivan Voras]

Author: ivoras
Date: Wed Dec 17 19:57:12 2008
New Revision: 186252
URL: http://svn.freebsd.org/changeset/base/186252

Log:
  Introduce a sysctl kern.vm_guest that reflects what the kernel knows about
  it running under a virtual environment. This also introduces a globally
  accessible variable vm_guest that can be used where appropriate in the
  kernel to inspect this environment.
  
  To make it easier for the long run, an enum VM_GUEST is also introduced,
  which could possibly be factored out in a header somewhere (but the
  question is where - vm/vm_param.h? sys/param.h?) so it eventually becomes
  a part of the standard KPI. In any case, it's a start.
  
  The purpose of all this isn't to absolutely detect that the OS is running
  under a virtual environment (cf. "redpill") but to allow the parts of the
  kernel and the userland that care about this particular aspect and can do
  something useful depending on it to have a standardised interface. Reducing
  kern.hz is one example but there are other things that could be done like
  avoiding context switches, not using CPU instructions that are known to be
  slow in emulation, possibly different strategies in VM (memory) allocation,
  CPU scheduling, etc.
  
  It isn't clear if the JAILS/VIMAGE functionality should also be exposed
  by this particular mechanism (probably not since they're not "full"
  virtual hardware environments). Sometime in the future another sysctl and
  a variable could be introduced to reflect if the kernel supports any kind
  of virtual hosting (e.g. VMWare VMI, Xen dom0).
  
  Reviewed by:	silence from src-commiters@, virtualization@, kmacy@
  Approved by:	gnn (mentor)
  Security:	Obscurity doesn't help.

Modified:
  head/sys/kern/subr_param.c

Modified: head/sys/kern/subr_param.c
==============================================================================
--- head/sys/kern/subr_param.c	Wed Dec 17 19:19:14 2008	(r186251)
+++ head/sys/kern/subr_param.c	Wed Dec 17 19:57:12 2008	(r186252)
@@ -73,6 +73,8 @@ __FBSDID("$FreeBSD$");
 #define	MAXFILES (maxproc * 2)
 #endif
 
+enum VM_GUEST { VM_GUEST_NO, VM_GUEST_VM, VM_GUEST_XEN };
+
 int	hz;
 int	tick;
 int	maxusers;			/* base tunable */
@@ -86,6 +88,7 @@ int	nswbuf;
 int	maxswzone;			/* max swmeta KVA storage */
 int	maxbcache;			/* max buffer cache KVA storage */
 int	maxpipekva;			/* Limit on pipe KVA */
+int	vm_guest;			/* Running as virtual machine guest? */
 u_long	maxtsiz;			/* max text size */
 u_long	dfldsiz;			/* initial data size limit */
 u_long	maxdsiz;			/* max data size */
@@ -110,6 +113,8 @@ SYSCTL_ULONG(_kern, OID_AUTO, maxssiz, C
     "max stack size");
 SYSCTL_ULONG(_kern, OID_AUTO, sgrowsiz, CTLFLAG_RDTUN, &sgrowsiz, 0,
     "amount to grow stack");
+SYSCTL_INT(_kern, OID_AUTO, vm_guest, CTLFLAG_RD, &vm_guest, 0,
+    "Running under a virtual machine?");
 
 /*
  * These have to be allocated somewhere; allocating
@@ -133,7 +138,7 @@ static const char *const vm_pnames[] = {
 	NULL
 };
 
-static int
+static enum VM_GUEST
 detect_virtual(void)
 {
 	char *sysenv;
@@ -144,7 +149,7 @@ detect_virtual(void)
 		for (i = 0; vm_bnames[i] != NULL; i++)
 			if (strcmp(sysenv, vm_bnames[i]) == 0) {
 				freeenv(sysenv);
-				return (1);
+				return (VM_GUEST_VM);
 			}
 		freeenv(sysenv);
 	}
@@ -153,11 +158,11 @@ detect_virtual(void)
 		for (i = 0; vm_pnames[i] != NULL; i++)
 			if (strcmp(sysenv, vm_pnames[i]) == 0) {
 				freeenv(sysenv);
-				return (1);
+				return (VM_GUEST_VM);
 			}
 		freeenv(sysenv);
 	}
-	return (0);
+	return (VM_GUEST_NO);
 }
 
 /*
@@ -166,11 +171,15 @@ detect_virtual(void)
 void
 init_param1(void)
 {
-
+#ifndef XEN
+	vm_guest = detect_virtual();
+#else
+	vm_guest = VM_GUEST_XEN;
+#endif
 	hz = -1;
 	TUNABLE_INT_FETCH("kern.hz", &hz);
 	if (hz == -1)
-		hz = detect_virtual() ? HZ_VM : HZ;
+		hz = vm_guest > VM_GUEST_NO ? HZ_VM : HZ;
 	tick = 1000000 / hz;
 
 #ifdef VM_SWZONE_SIZE_MAX