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Subject[GIT PULL] x86/fpu updates for v3.20
Linus,

Please pull the latest x86-fpu-for-linus git tree from:

git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git x86-fpu-for-linus

# HEAD: 7575637ab293861a799f3bbafe0d8c597389f4e9 x86, fpu: Fix math_state_restore() race with kernel_fpu_begin()

Initial round of kernel_fpu_begin/end cleanups from Oleg
Nesterov, plus a cleanup from Borislav Petkov.

Thanks,

Ingo

------------------>
Borislav Petkov (1):
x86/fpu: Use a symbolic name for asm operand

Oleg Nesterov (3):
x86, fpu: Introduce per-cpu in_kernel_fpu state
x86, fpu: Don't abuse has_fpu in __kernel_fpu_begin/end()
x86, fpu: Fix math_state_restore() race with kernel_fpu_begin()


arch/x86/include/asm/fpu-internal.h | 10 ++++++----
arch/x86/include/asm/i387.h | 6 +++++-
arch/x86/kernel/i387.c | 39 ++++++++++++++++++++++++-------------
arch/x86/kernel/traps.c | 12 +++++-------
4 files changed, 42 insertions(+), 25 deletions(-)

diff --git a/arch/x86/include/asm/fpu-internal.h b/arch/x86/include/asm/fpu-internal.h
index e97622f57722..0dbc08282291 100644
--- a/arch/x86/include/asm/fpu-internal.h
+++ b/arch/x86/include/asm/fpu-internal.h
@@ -207,7 +207,7 @@ static inline void fpu_fxsave(struct fpu *fpu)
if (config_enabled(CONFIG_X86_32))
asm volatile( "fxsave %[fx]" : [fx] "=m" (fpu->state->fxsave));
else if (config_enabled(CONFIG_AS_FXSAVEQ))
- asm volatile("fxsaveq %0" : "=m" (fpu->state->fxsave));
+ asm volatile("fxsaveq %[fx]" : [fx] "=m" (fpu->state->fxsave));
else {
/* Using "rex64; fxsave %0" is broken because, if the memory
* operand uses any extended registers for addressing, a second
@@ -290,9 +290,11 @@ static inline int fpu_restore_checking(struct fpu *fpu)

static inline int restore_fpu_checking(struct task_struct *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
- values. "m" is a random variable that should be in L1 */
+ /*
+ * 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 values.
+ * "m" is a random variable that should be in L1.
+ */
if (unlikely(static_cpu_has_bug_safe(X86_BUG_FXSAVE_LEAK))) {
asm volatile(
"fnclex\n\t"
diff --git a/arch/x86/include/asm/i387.h b/arch/x86/include/asm/i387.h
index ed8089d69094..6eb6fcb83f63 100644
--- a/arch/x86/include/asm/i387.h
+++ b/arch/x86/include/asm/i387.h
@@ -40,8 +40,8 @@ extern void __kernel_fpu_end(void);

static inline void kernel_fpu_begin(void)
{
- WARN_ON_ONCE(!irq_fpu_usable());
preempt_disable();
+ WARN_ON_ONCE(!irq_fpu_usable());
__kernel_fpu_begin();
}

@@ -51,6 +51,10 @@ static inline void kernel_fpu_end(void)
preempt_enable();
}

+/* Must be called with preempt disabled */
+extern void kernel_fpu_disable(void);
+extern void kernel_fpu_enable(void);
+
/*
* Some instructions like VIA's padlock instructions generate a spurious
* DNA fault but don't modify SSE registers. And these instructions
diff --git a/arch/x86/kernel/i387.c b/arch/x86/kernel/i387.c
index a9a4229f6161..81049ffab2d6 100644
--- a/arch/x86/kernel/i387.c
+++ b/arch/x86/kernel/i387.c
@@ -19,6 +19,19 @@
#include <asm/fpu-internal.h>
#include <asm/user.h>

+static DEFINE_PER_CPU(bool, in_kernel_fpu);
+
+void kernel_fpu_disable(void)
+{
+ WARN_ON(this_cpu_read(in_kernel_fpu));
+ this_cpu_write(in_kernel_fpu, true);
+}
+
+void kernel_fpu_enable(void)
+{
+ this_cpu_write(in_kernel_fpu, false);
+}
+
/*
* Were we in an interrupt that interrupted kernel mode?
*
@@ -33,6 +46,9 @@
*/
static inline bool interrupted_kernel_fpu_idle(void)
{
+ if (this_cpu_read(in_kernel_fpu))
+ return false;
+
if (use_eager_fpu())
return __thread_has_fpu(current);

@@ -73,10 +89,10 @@ void __kernel_fpu_begin(void)
{
struct task_struct *me = current;

+ this_cpu_write(in_kernel_fpu, true);
+
if (__thread_has_fpu(me)) {
- __thread_clear_has_fpu(me);
__save_init_fpu(me);
- /* We do 'stts()' in __kernel_fpu_end() */
} else if (!use_eager_fpu()) {
this_cpu_write(fpu_owner_task, NULL);
clts();
@@ -86,19 +102,16 @@ EXPORT_SYMBOL(__kernel_fpu_begin);

void __kernel_fpu_end(void)
{
- if (use_eager_fpu()) {
- /*
- * For eager fpu, most the time, tsk_used_math() is true.
- * Restore the user math as we are done with the kernel usage.
- * At few instances during thread exit, signal handling etc,
- * tsk_used_math() is false. Those few places will take proper
- * actions, so we don't need to restore the math here.
- */
- if (likely(tsk_used_math(current)))
- math_state_restore();
- } else {
+ struct task_struct *me = current;
+
+ if (__thread_has_fpu(me)) {
+ if (WARN_ON(restore_fpu_checking(me)))
+ drop_init_fpu(me);
+ } else if (!use_eager_fpu()) {
stts();
}
+
+ this_cpu_write(in_kernel_fpu, false);
}
EXPORT_SYMBOL(__kernel_fpu_end);

diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 88900e288021..fb4cb6adf225 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -788,18 +788,16 @@ void math_state_restore(void)
local_irq_disable();
}

+ /* Avoid __kernel_fpu_begin() right after __thread_fpu_begin() */
+ kernel_fpu_disable();
__thread_fpu_begin(tsk);
-
- /*
- * Paranoid restore. send a SIGSEGV if we fail to restore the state.
- */
if (unlikely(restore_fpu_checking(tsk))) {
drop_init_fpu(tsk);
force_sig_info(SIGSEGV, SEND_SIG_PRIV, tsk);
- return;
+ } else {
+ tsk->thread.fpu_counter++;
}
-
- tsk->thread.fpu_counter++;
+ kernel_fpu_enable();
}
EXPORT_SYMBOL_GPL(math_state_restore);


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