This patch splits get_cycles_sync() into __get_cycles_sync(),
and the rdtscll part. Paravirt guests cannot issue rdtscl directly,
as it involves a function call in vdso area.
So, using the __get_cycles_sync() base, we introduce vget_cycles_sync,
which then calls the native version of rdtscll. Ideally, however, a guest
should define its own clocksource, together with a vread function
Signed-off-by: Glauber de Oliveira Costa <[email protected]>
---
arch/x86/kernel/tsc_64.c | 2 +-
include/asm-x86/tsc.h | 37 +++++++++++++++++++++++++++++++++----
2 files changed, 34 insertions(+), 5 deletions(-)
diff --git a/arch/x86/kernel/tsc_64.c b/arch/x86/kernel/tsc_64.c
index 5158476..4502539 100644
--- a/arch/x86/kernel/tsc_64.c
+++ b/arch/x86/kernel/tsc_64.c
@@ -269,7 +269,7 @@ 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/include/asm-x86/tsc.h b/include/asm-x86/tsc.h
index 6baab30..d6cb056 100644
--- a/include/asm-x86/tsc.h
+++ b/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);
--
1.4.4.2
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