From ea438cd7236d7a5d4aa9e6ae4c10e46d1ffea563 Mon Sep 17 00:00:00 2001
From: Glauber de Oliveira Costa <gcosta@redhat.com>
Date: Wed, 30 Jan 2008 13:31:03 +0100
Subject: [PATCH] --- yaml --- r: 79927 b: refs/heads/master c:
 4e87173eacfd0d798aeeba14026893797826bc93 h: refs/heads/master i:   79925:
 1430b389cc7367493b7042865cec5e307bc5430d   79923:
 10a902e90baeea0e8b7468838d8f60d66485c2ea   79919:
 d850607a46d0e58bdd8acf0f3893269ac3445825 v: v3

---
 [refs]                         |  2 +-
 trunk/arch/x86/kernel/tsc_64.c |  2 +-
 trunk/include/asm-x86/tsc.h    | 37 ++++++++++++++++++++++++++++++----
 3 files changed, 35 insertions(+), 6 deletions(-)

diff --git a/[refs] b/[refs]
index 9862146c06ca..368078a4ffb3 100644
--- a/[refs]
+++ b/[refs]
@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 16e2011be67b8625c1c600f9742c2279be3c0c68
+refs/heads/master: 4e87173eacfd0d798aeeba14026893797826bc93
diff --git a/trunk/arch/x86/kernel/tsc_64.c b/trunk/arch/x86/kernel/tsc_64.c
index 204a9080af04..3723401c4593 100644
--- a/trunk/arch/x86/kernel/tsc_64.c
+++ b/trunk/arch/x86/kernel/tsc_64.c
@@ -306,7 +306,7 @@ static cycle_t read_tsc(void)
 
 static cycle_t __vsyscall_fn vread_tsc(void)
 {
-	cycle_t ret = (cycle_t)get_cycles_sync();
+	cycle_t ret = (cycle_t)vget_cycles_sync();
 	return ret;
 }
 
diff --git a/trunk/include/asm-x86/tsc.h b/trunk/include/asm-x86/tsc.h
index d7b1c4e7a108..9b7d264897fa 100644
--- a/trunk/include/asm-x86/tsc.h
+++ b/trunk/include/asm-x86/tsc.h
@@ -33,14 +33,14 @@ static inline cycles_t get_cycles(void)
 }
 
 /* Like get_cycles, but make sure the CPU is synchronized. */
-static __always_inline cycles_t get_cycles_sync(void)
+static __always_inline cycles_t __get_cycles_sync(void)
 {
 	unsigned long long ret;
 	unsigned eax, edx;
 
 	/*
-  	 * Use RDTSCP if possible; it is guaranteed to be synchronous
- 	 * and doesn't cause a VMEXIT on Hypervisors
+	 * Use RDTSCP if possible; it is guaranteed to be synchronous
+	 * and doesn't cause a VMEXIT on Hypervisors
 	 */
 	alternative_io(ASM_NOP3, ".byte 0x0f,0x01,0xf9", X86_FEATURE_RDTSCP,
 		       ASM_OUTPUT2("=a" (eax), "=d" (edx)),
@@ -55,11 +55,40 @@ static __always_inline cycles_t get_cycles_sync(void)
 	 */
 	alternative_io("cpuid", ASM_NOP2, X86_FEATURE_SYNC_RDTSC,
 			  "=a" (eax), "0" (1) : "ebx","ecx","edx","memory");
-	rdtscll(ret);
 
+	return 0;
+}
+
+static __always_inline cycles_t get_cycles_sync(void)
+{
+	unsigned long long ret;
+	ret = __get_cycles_sync();
+	if (!ret)
+		rdtscll(ret);
 	return ret;
 }
 
+#ifdef CONFIG_PARAVIRT
+/*
+ * For paravirt guests, some functionalities are executed through function
+ * pointers in the various pvops structures.
+ * These function pointers exist inside the kernel and can not
+ * be accessed by user space. To avoid this, we make a copy of the
+ * get_cycles_sync (called in kernel) but force the use of native_read_tsc.
+ * Ideally, the guest should set up it's own clock and vread
+ */
+static __always_inline long long vget_cycles_sync(void)
+{
+	unsigned long long ret;
+	ret = __get_cycles_sync();
+	if (!ret)
+		ret = native_read_tsc();
+	return ret;
+}
+#else
+# define vget_cycles_sync() get_cycles_sync()
+#endif
+
 extern void tsc_init(void);
 extern void mark_tsc_unstable(char *reason);
 extern int unsynchronized_tsc(void);