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authorLinus Torvalds <torvalds@linux-foundation.org>2012-02-17 21:48:54 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2012-02-18 10:19:41 -0800
commitf94edacf998516ac9d849f7bc6949a703977a7f3 (patch)
tree4a5c5487d86f3b3873b8ca1ba1c0b00b832870ad
parent4903062b5485f0e2c286a23b44c9b59d9b017d53 (diff)
i387: move TS_USEDFPU flag from thread_info to task_struct
This moves the bit that indicates whether a thread has ownership of the FPU from the TS_USEDFPU bit in thread_info->status to a word of its own (called 'has_fpu') in task_struct->thread.has_fpu. This fixes two independent bugs at the same time: - changing 'thread_info->status' from the scheduler causes nasty problems for the other users of that variable, since it is defined to be thread-synchronous (that's what the "TS_" part of the naming was supposed to indicate). So perfectly valid code could (and did) do ti->status |= TS_RESTORE_SIGMASK; and the compiler was free to do that as separate load, or and store instructions. Which can cause problems with preemption, since a task switch could happen in between, and change the TS_USEDFPU bit. The change to TS_USEDFPU would be overwritten by the final store. In practice, this seldom happened, though, because the 'status' field was seldom used more than once, so gcc would generally tend to generate code that used a read-modify-write instruction and thus happened to avoid this problem - RMW instructions are naturally low fat and preemption-safe. - On x86-32, the current_thread_info() pointer would, during interrupts and softirqs, point to a *copy* of the real thread_info, because x86-32 uses %esp to calculate the thread_info address, and thus the separate irq (and softirq) stacks would cause these kinds of odd thread_info copy aliases. This is normally not a problem, since interrupts aren't supposed to look at thread information anyway (what thread is running at interrupt time really isn't very well-defined), but it confused the heck out of irq_fpu_usable() and the code that tried to squirrel away the FPU state. (It also caused untold confusion for us poor kernel developers). It also turns out that using 'task_struct' is actually much more natural for most of the call sites that care about the FPU state, since they tend to work with the task struct for other reasons anyway (ie scheduling). And the FPU data that we are going to save/restore is found there too. Thanks to Arjan Van De Ven <arjan@linux.intel.com> for pointing us to the %esp issue. Cc: Arjan van de Ven <arjan@linux.intel.com> Reported-and-tested-by: Raphael Prevost <raphael@buro.asia> Acked-and-tested-by: Suresh Siddha <suresh.b.siddha@intel.com> Tested-by: Peter Anvin <hpa@zytor.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--arch/x86/include/asm/i387.h44
-rw-r--r--arch/x86/include/asm/processor.h1
-rw-r--r--arch/x86/include/asm/thread_info.h2
-rw-r--r--arch/x86/kernel/traps.c11
-rw-r--r--arch/x86/kernel/xsave.c2
-rw-r--r--arch/x86/kvm/vmx.c2
6 files changed, 30 insertions, 32 deletions
diff --git a/arch/x86/include/asm/i387.h b/arch/x86/include/asm/i387.h
index 01b115d8677..f5376676f89 100644
--- a/arch/x86/include/asm/i387.h
+++ b/arch/x86/include/asm/i387.h
@@ -264,21 +264,21 @@ static inline int restore_fpu_checking(struct task_struct *tsk)
* be preemption protection *and* they need to be
* properly paired with the CR0.TS changes!
*/
-static inline int __thread_has_fpu(struct thread_info *ti)
+static inline int __thread_has_fpu(struct task_struct *tsk)
{
- return ti->status & TS_USEDFPU;
+ return tsk->thread.has_fpu;
}
/* Must be paired with an 'stts' after! */
-static inline void __thread_clear_has_fpu(struct thread_info *ti)
+static inline void __thread_clear_has_fpu(struct task_struct *tsk)
{
- ti->status &= ~TS_USEDFPU;
+ tsk->thread.has_fpu = 0;
}
/* Must be paired with a 'clts' before! */
-static inline void __thread_set_has_fpu(struct thread_info *ti)
+static inline void __thread_set_has_fpu(struct task_struct *tsk)
{
- ti->status |= TS_USEDFPU;
+ tsk->thread.has_fpu = 1;
}
/*
@@ -288,16 +288,16 @@ static inline void __thread_set_has_fpu(struct thread_info *ti)
* These generally need preemption protection to work,
* do try to avoid using these on their own.
*/
-static inline void __thread_fpu_end(struct thread_info *ti)
+static inline void __thread_fpu_end(struct task_struct *tsk)
{
- __thread_clear_has_fpu(ti);
+ __thread_clear_has_fpu(tsk);
stts();
}
-static inline void __thread_fpu_begin(struct thread_info *ti)
+static inline void __thread_fpu_begin(struct task_struct *tsk)
{
clts();
- __thread_set_has_fpu(ti);
+ __thread_set_has_fpu(tsk);
}
/*
@@ -308,21 +308,21 @@ extern int restore_i387_xstate(void __user *buf);
static inline void __unlazy_fpu(struct task_struct *tsk)
{
- if (__thread_has_fpu(task_thread_info(tsk))) {
+ if (__thread_has_fpu(tsk)) {
__save_init_fpu(tsk);
- __thread_fpu_end(task_thread_info(tsk));
+ __thread_fpu_end(tsk);
} else
tsk->fpu_counter = 0;
}
static inline void __clear_fpu(struct task_struct *tsk)
{
- if (__thread_has_fpu(task_thread_info(tsk))) {
+ if (__thread_has_fpu(tsk)) {
/* Ignore delayed exceptions from user space */
asm volatile("1: fwait\n"
"2:\n"
_ASM_EXTABLE(1b, 2b));
- __thread_fpu_end(task_thread_info(tsk));
+ __thread_fpu_end(tsk);
}
}
@@ -337,7 +337,7 @@ static inline void __clear_fpu(struct task_struct *tsk)
*/
static inline bool interrupted_kernel_fpu_idle(void)
{
- return !__thread_has_fpu(current_thread_info()) &&
+ return !__thread_has_fpu(current) &&
(read_cr0() & X86_CR0_TS);
}
@@ -371,12 +371,12 @@ static inline bool irq_fpu_usable(void)
static inline void kernel_fpu_begin(void)
{
- struct thread_info *me = current_thread_info();
+ struct task_struct *me = current;
WARN_ON_ONCE(!irq_fpu_usable());
preempt_disable();
if (__thread_has_fpu(me)) {
- __save_init_fpu(me->task);
+ __save_init_fpu(me);
__thread_clear_has_fpu(me);
/* We do 'stts()' in kernel_fpu_end() */
} else
@@ -441,13 +441,13 @@ static inline void irq_ts_restore(int TS_state)
*/
static inline int user_has_fpu(void)
{
- return __thread_has_fpu(current_thread_info());
+ return __thread_has_fpu(current);
}
static inline void user_fpu_end(void)
{
preempt_disable();
- __thread_fpu_end(current_thread_info());
+ __thread_fpu_end(current);
preempt_enable();
}
@@ -455,7 +455,7 @@ static inline void user_fpu_begin(void)
{
preempt_disable();
if (!user_has_fpu())
- __thread_fpu_begin(current_thread_info());
+ __thread_fpu_begin(current);
preempt_enable();
}
@@ -464,10 +464,10 @@ static inline void user_fpu_begin(void)
*/
static inline void save_init_fpu(struct task_struct *tsk)
{
- WARN_ON_ONCE(!__thread_has_fpu(task_thread_info(tsk)));
+ WARN_ON_ONCE(!__thread_has_fpu(tsk));
preempt_disable();
__save_init_fpu(tsk);
- __thread_fpu_end(task_thread_info(tsk));
+ __thread_fpu_end(tsk);
preempt_enable();
}
diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index aa9088c2693..f7c89e231c6 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -454,6 +454,7 @@ struct thread_struct {
unsigned long trap_no;
unsigned long error_code;
/* floating point and extended processor state */
+ unsigned long has_fpu;
struct fpu fpu;
#ifdef CONFIG_X86_32
/* Virtual 86 mode info */
diff --git a/arch/x86/include/asm/thread_info.h b/arch/x86/include/asm/thread_info.h
index bc817cd8b44..cfd8144d552 100644
--- a/arch/x86/include/asm/thread_info.h
+++ b/arch/x86/include/asm/thread_info.h
@@ -247,8 +247,6 @@ static inline struct thread_info *current_thread_info(void)
* ever touches our thread-synchronous status, so we don't
* have to worry about atomic accesses.
*/
-#define TS_USEDFPU 0x0001 /* FPU was used by this task
- this quantum (SMP) */
#define TS_COMPAT 0x0002 /* 32bit syscall active (64BIT)*/
#define TS_POLLING 0x0004 /* idle task polling need_resched,
skip sending interrupt */
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 4d42300dcd2..ad25e51f40c 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -582,12 +582,11 @@ asmlinkage void __attribute__((weak)) smp_threshold_interrupt(void)
*/
void math_state_restore(void)
{
- struct thread_info *thread = current_thread_info();
- struct task_struct *tsk = thread->task;
+ struct task_struct *tsk = current;
/* We need a safe address that is cheap to find and that is already
- in L1. We just brought in "thread->task", so use that */
-#define safe_address (thread->task)
+ in L1. We're just bringing in "tsk->thread.has_fpu", so use that */
+#define safe_address (tsk->thread.has_fpu)
if (!tsk_used_math(tsk)) {
local_irq_enable();
@@ -604,7 +603,7 @@ void math_state_restore(void)
local_irq_disable();
}
- __thread_fpu_begin(thread);
+ __thread_fpu_begin(tsk);
/* AMD K7/K8 CPUs don't save/restore FDP/FIP/FOP unless an exception
is pending. Clear the x87 state here by setting it to fixed
@@ -620,7 +619,7 @@ void math_state_restore(void)
* Paranoid restore. send a SIGSEGV if we fail to restore the state.
*/
if (unlikely(restore_fpu_checking(tsk))) {
- __thread_fpu_end(thread);
+ __thread_fpu_end(tsk);
force_sig(SIGSEGV, tsk);
return;
}
diff --git a/arch/x86/kernel/xsave.c b/arch/x86/kernel/xsave.c
index a0bcd0dbc95..71109111411 100644
--- a/arch/x86/kernel/xsave.c
+++ b/arch/x86/kernel/xsave.c
@@ -47,7 +47,7 @@ void __sanitize_i387_state(struct task_struct *tsk)
if (!fx)
return;
- BUG_ON(__thread_has_fpu(task_thread_info(tsk)));
+ BUG_ON(__thread_has_fpu(tsk));
xstate_bv = tsk->thread.fpu.state->xsave.xsave_hdr.xstate_bv;
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 36091dd04b4..3b4c8d8ad90 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -1457,7 +1457,7 @@ static void __vmx_load_host_state(struct vcpu_vmx *vmx)
#ifdef CONFIG_X86_64
wrmsrl(MSR_KERNEL_GS_BASE, vmx->msr_host_kernel_gs_base);
#endif
- if (__thread_has_fpu(current_thread_info()))
+ if (__thread_has_fpu(current))
clts();
load_gdt(&__get_cpu_var(host_gdt));
}