svn commit: r312724 - in head/sys: sys vm

[Mateusz Guzik]

Author: mjg
Date: Tue Jan 24 22:00:16 2017
New Revision: 312724
URL: https://svnweb.freebsd.org/changeset/base/312724

Log:
  hwpmc: partially depessimize munmap handling if the module is not loaded
  
  HWPMC_HOOKS is enabled in GENERIC and triggers some work avoidable in the
  common (module not loaded) case.
  
  In particular this avoids permission checks + lock downgrade
  singlethreaded and in cases were an executable mapping is found the pmc
  sx lock is no longer bounced.
  
  Note this is a band aid.
  
  MFC after:	1 week

Modified:
  head/sys/sys/pmckern.h
  head/sys/vm/vm_mmap.c

Modified: head/sys/sys/pmckern.h
==============================================================================
--- head/sys/sys/pmckern.h	Tue Jan 24 21:48:57 2017	(r312723)
+++ head/sys/sys/pmckern.h	Tue Jan 24 22:00:16 2017	(r312724)
@@ -174,6 +174,9 @@ extern const int pmc_kernel_version;
 /* PMC soft per cpu trapframe */
 extern struct trapframe pmc_tf[MAXCPU];
 
+/* Quick check if preparatory work is necessary */
+#define	PMC_HOOK_INSTALLED(cmd)	__predict_false(pmc_hook != NULL)
+
 /* Hook invocation; for use within the kernel */
 #define	PMC_CALL_HOOK(t, cmd, arg)		\
 do {						\

Modified: head/sys/vm/vm_mmap.c
==============================================================================
--- head/sys/vm/vm_mmap.c	Tue Jan 24 21:48:57 2017	(r312723)
+++ head/sys/vm/vm_mmap.c	Tue Jan 24 22:00:16 2017	(r312724)
@@ -526,6 +526,7 @@ sys_munmap(td, uap)
 #ifdef HWPMC_HOOKS
 	struct pmckern_map_out pkm;
 	vm_map_entry_t entry;
+	bool pmc_handled;
 #endif
 	vm_offset_t addr;
 	vm_size_t size, pageoff;
@@ -551,20 +552,24 @@ sys_munmap(td, uap)
 		return (EINVAL);
 	vm_map_lock(map);
 #ifdef HWPMC_HOOKS
-	/*
-	 * Inform hwpmc if the address range being unmapped contains
-	 * an executable region.
-	 */
-	pkm.pm_address = (uintptr_t) NULL;
-	if (vm_map_lookup_entry(map, addr, &entry)) {
-		for (;
-		     entry != &map->header && entry->start < addr + size;
-		     entry = entry->next) {
-			if (vm_map_check_protection(map, entry->start,
-				entry->end, VM_PROT_EXECUTE) == TRUE) {
-				pkm.pm_address = (uintptr_t) addr;
-				pkm.pm_size = (size_t) size;
-				break;
+	pmc_handled = false;
+	if (PMC_HOOK_INSTALLED(PMC_FN_MUNMAP)) {
+		pmc_handled = true;
+		/*
+		 * Inform hwpmc if the address range being unmapped contains
+		 * an executable region.
+		 */
+		pkm.pm_address = (uintptr_t) NULL;
+		if (vm_map_lookup_entry(map, addr, &entry)) {
+			for (;
+			    entry != &map->header && entry->start < addr + size;
+			    entry = entry->next) {
+				if (vm_map_check_protection(map, entry->start,
+					entry->end, VM_PROT_EXECUTE) == TRUE) {
+					pkm.pm_address = (uintptr_t) addr;
+					pkm.pm_size = (size_t) size;
+					break;
+				}
 			}
 		}
 	}
@@ -572,14 +577,16 @@ sys_munmap(td, uap)
 	vm_map_delete(map, addr, addr + size);
 
 #ifdef HWPMC_HOOKS
-	/* downgrade the lock to prevent a LOR with the pmc-sx lock */
-	vm_map_lock_downgrade(map);
-	if (pkm.pm_address != (uintptr_t) NULL)
-		PMC_CALL_HOOK(td, PMC_FN_MUNMAP, (void *) &pkm);
-	vm_map_unlock_read(map);
-#else
-	vm_map_unlock(map);
+	if (__predict_false(pmc_handled)) {
+		/* downgrade the lock to prevent a LOR with the pmc-sx lock */
+		vm_map_lock_downgrade(map);
+		if (pkm.pm_address != (uintptr_t) NULL)
+			PMC_CALL_HOOK(td, PMC_FN_MUNMAP, (void *) &pkm);
+		vm_map_unlock_read(map);
+	} else
 #endif
+		vm_map_unlock(map);
+
 	/* vm_map_delete returns nothing but KERN_SUCCESS anyway */
 	return (0);
 }