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authorErik Bosman <ejbosman@cs.vu.nl>2008-04-14 00:24:18 +0200
committerIngo Molnar <mingo@elte.hu>2008-04-19 19:19:55 +0200
commit529e25f646e08901a6dad5768f681efffd77225e (patch)
treea284d6511b6eef0ab83a3e9ada7a6ae300a33010 /arch/x86/kernel/process_64.c
parent8fb402bccf203ecca8f9e0202b8fd3c937dece6f (diff)
x86: implement prctl PR_GET_TSC and PR_SET_TSC
This patch implements the PR_GET_TSC and PR_SET_TSC prctl() commands on the x86 platform (both 32 and 64 bit.) These commands control the ability to read the timestamp counter from userspace (the RDTSC instruction.) While the RDTSC instuction is a useful profiling tool, it is also the source of some non-determinism in ring-3. For deterministic replay applications it is useful to be able to trap and emulate (and record the outcome of) this instruction. This patch uses code earlier used to disable the timestamp counter for the SECCOMP framework. A side-effect of this patch is that the SECCOMP environment will now also disable the timestamp counter on x86_64 due to the addition of the TIF_NOTSC define on this platform. The code which enables/disables the RDTSC instruction during context switches is in the __switch_to_xtra function, which already handles other unusual conditions, so normal performance should not have to suffer from this change. Signed-off-by: Erik Bosman <ejbosman@cs.vu.nl> Acked-by: Arjan van de Ven <arjan@linux.intel.com> Signed-off-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Diffstat (limited to 'arch/x86/kernel/process_64.c')
-rw-r--r--arch/x86/kernel/process_64.c68
1 files changed, 68 insertions, 0 deletions
diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index e75ccc8a2b87..4c13b1406c70 100644
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -36,6 +36,7 @@
#include <linux/kprobes.h>
#include <linux/kdebug.h>
#include <linux/tick.h>
+#include <linux/prctl.h>
#include <asm/uaccess.h>
#include <asm/pgtable.h>
@@ -535,6 +536,64 @@ start_thread(struct pt_regs *regs, unsigned long new_ip, unsigned long new_sp)
}
EXPORT_SYMBOL_GPL(start_thread);
+static void hard_disable_TSC(void)
+{
+ write_cr4(read_cr4() | X86_CR4_TSD);
+}
+
+void disable_TSC(void)
+{
+ preempt_disable();
+ if (!test_and_set_thread_flag(TIF_NOTSC))
+ /*
+ * Must flip the CPU state synchronously with
+ * TIF_NOTSC in the current running context.
+ */
+ hard_disable_TSC();
+ preempt_enable();
+}
+
+static void hard_enable_TSC(void)
+{
+ write_cr4(read_cr4() & ~X86_CR4_TSD);
+}
+
+void enable_TSC(void)
+{
+ preempt_disable();
+ if (test_and_clear_thread_flag(TIF_NOTSC))
+ /*
+ * Must flip the CPU state synchronously with
+ * TIF_NOTSC in the current running context.
+ */
+ hard_enable_TSC();
+ preempt_enable();
+}
+
+int get_tsc_mode(unsigned long adr)
+{
+ unsigned int val;
+
+ if (test_thread_flag(TIF_NOTSC))
+ val = PR_TSC_SIGSEGV;
+ else
+ val = PR_TSC_ENABLE;
+
+ return put_user(val, (unsigned int __user *)adr);
+}
+
+int set_tsc_mode(unsigned int val)
+{
+ if (val == PR_TSC_SIGSEGV)
+ disable_TSC();
+ else if (val == PR_TSC_ENABLE)
+ enable_TSC();
+ else
+ return -EINVAL;
+
+ return 0;
+}
+
/*
* This special macro can be used to load a debugging register
*/
@@ -572,6 +631,15 @@ static inline void __switch_to_xtra(struct task_struct *prev_p,
loaddebug(next, 7);
}
+ if (test_tsk_thread_flag(prev_p, TIF_NOTSC) ^
+ test_tsk_thread_flag(next_p, TIF_NOTSC)) {
+ /* prev and next are different */
+ if (test_tsk_thread_flag(next_p, TIF_NOTSC))
+ hard_disable_TSC();
+ else
+ hard_enable_TSC();
+ }
+
if (test_tsk_thread_flag(next_p, TIF_IO_BITMAP)) {
/*
* Copy the relevant range of the IO bitmap.