Fundamental model of the current Linux kernel is to lazily init and
restore FPU instead of restoring the task state during context switch.
This changes that fundamental lazy model to the non-lazy model for
the processors supporting xsave feature.
Reasons driving this model change are:
i. Newer processors support optimized state save/restore using xsaveopt and
xrstor by tracking the INIT state and MODIFIED state during context-switch.
This is faster than modifying the cr0.TS bit which has serializing semantics.
ii. Newer glibc versions use SSE for some of the optimized copy/clear routines.
With certain workloads (like boot, kernel-compilation etc), application
completes its work with in the first 5 task switches, thus taking upto 5 #DNA
traps with the kernel not getting a chance to apply the above mentioned
pre-load heuristic.
iii. Some xstate features (like AMD's LWP feature) don't honor the cr0.TS bit
and thus will not work correctly in the presence of lazy restore. Non-lazy
state restore is needed for enabling such features.
Some data on a two socket SNB system:
* Saved 20K DNA exceptions during boot on a two socket SNB system.
* Saved 50K DNA exceptions during kernel-compilation workload.
* Improved throughput of the AVX based checksumming function inside the
kernel by ~15% as xsave/xrstor is faster than the serializing clts/stts
pair.
Also now kernel_fpu_begin/end() relies on the patched
alternative instructions. So move check_fpu() which uses the
kernel_fpu_begin/end() after alternative_instructions().
Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
Link: http://lkml.kernel.org/r/1345842782-24175-7-git-send-email-suresh.b.siddha@intel.com
Merge 32-bit boot fix from,
Link: http://lkml.kernel.org/r/1347300665-6209-4-git-send-email-suresh.b.siddha@intel.com
Cc: Jim Kukunas <james.t.kukunas@linux.intel.com>
Cc: NeilBrown <neilb@suse.de>
Cc: Avi Kivity <avi@redhat.com>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
static inline void __thread_fpu_end(struct task_struct *tsk)
{
__thread_clear_has_fpu(tsk);
- stts();
+ if (!use_xsave())
+ stts();
}
static inline void __thread_fpu_begin(struct task_struct *tsk)
{
- clts();
+ if (!use_xsave())
+ clts();
__thread_set_has_fpu(tsk);
}
+static inline void __drop_fpu(struct task_struct *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(tsk);
+ }
+}
+
+static inline void drop_fpu(struct task_struct *tsk)
+{
+ /*
+ * Forget coprocessor state..
+ */
+ preempt_disable();
+ tsk->fpu_counter = 0;
+ __drop_fpu(tsk);
+ clear_used_math();
+ preempt_enable();
+}
+
+static inline void drop_init_fpu(struct task_struct *tsk)
+{
+ if (!use_xsave())
+ drop_fpu(tsk);
+ else
+ xrstor_state(init_xstate_buf, -1);
+}
+
/*
* FPU state switching for scheduling.
*
{
fpu_switch_t fpu;
- fpu.preload = tsk_used_math(new) && new->fpu_counter > 5;
+ /*
+ * If the task has used the math, pre-load the FPU on xsave processors
+ * or if the past 5 consecutive context-switches used math.
+ */
+ fpu.preload = tsk_used_math(new) && (use_xsave() ||
+ new->fpu_counter > 5);
if (__thread_has_fpu(old)) {
if (!__save_init_fpu(old))
cpu = ~0;
new->fpu_counter++;
__thread_set_has_fpu(new);
prefetch(new->thread.fpu.state);
- } else
+ } else if (!use_xsave())
stts();
} else {
old->fpu_counter = 0;
old->thread.fpu.last_cpu = ~0;
if (fpu.preload) {
new->fpu_counter++;
- if (fpu_lazy_restore(new, cpu))
+ if (!use_xsave() && fpu_lazy_restore(new, cpu))
fpu.preload = 0;
else
prefetch(new->thread.fpu.state);
{
if (fpu.preload) {
if (unlikely(restore_fpu_checking(new)))
- __thread_fpu_end(new);
+ drop_init_fpu(new);
}
}
return __restore_xstate_sig(buf, buf_fx, size);
}
-static inline void __drop_fpu(struct task_struct *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(tsk);
- }
-}
-
/*
* Need to be preemption-safe.
*
static inline void save_init_fpu(struct task_struct *tsk)
{
WARN_ON_ONCE(!__thread_has_fpu(tsk));
+
+ if (use_xsave()) {
+ xsave_state(&tsk->thread.fpu.state->xsave, -1);
+ return;
+ }
+
preempt_disable();
__save_init_fpu(tsk);
__thread_fpu_end(tsk);
preempt_enable();
}
-static inline void drop_fpu(struct task_struct *tsk)
-{
- /*
- * Forget coprocessor state..
- */
- tsk->fpu_counter = 0;
- preempt_disable();
- __drop_fpu(tsk);
- preempt_enable();
- clear_used_math();
-}
-
/*
* i387 state interaction
*/
}
}
-static inline void fpu_copy(struct fpu *dst, struct fpu *src)
+static inline void fpu_copy(struct task_struct *dst, struct task_struct *src)
{
- memcpy(dst->state, src->state, xstate_size);
-}
+ if (use_xsave()) {
+ struct xsave_struct *xsave = &dst->thread.fpu.state->xsave;
-extern void fpu_finit(struct fpu *fpu);
+ memset(&xsave->xsave_hdr, 0, sizeof(struct xsave_hdr_struct));
+ xsave_state(xsave, -1);
+ } else {
+ struct fpu *dfpu = &dst->thread.fpu;
+ struct fpu *sfpu = &src->thread.fpu;
+
+ unlazy_fpu(src);
+ memcpy(dfpu->state, sfpu->state, xstate_size);
+ }
+}
static inline unsigned long
alloc_mathframe(unsigned long sp, int ia32_frame, unsigned long *buf_fx,
struct user_i387_struct;
extern int init_fpu(struct task_struct *child);
+extern void fpu_finit(struct fpu *fpu);
extern int dump_fpu(struct pt_regs *, struct user_i387_struct *);
extern void math_state_restore(void);
extern unsigned int xstate_size;
extern u64 pcntxt_mask;
extern u64 xstate_fx_sw_bytes[USER_XSTATE_FX_SW_WORDS];
+extern struct xsave_struct *init_xstate_buf;
extern void xsave_init(void);
extern void update_regset_xstate_info(unsigned int size, u64 xstate_mask);
print_cpu_info(&boot_cpu_data);
#endif
check_config();
- check_fpu();
check_hlt();
check_popad();
init_utsname()->machine[1] =
'0' + (boot_cpu_data.x86 > 6 ? 6 : boot_cpu_data.x86);
alternative_instructions();
+
+ /*
+ * kernel_fpu_begin/end() in check_fpu() relies on the patched
+ * alternative instructions.
+ */
+ check_fpu();
}
/*
* Were we in an interrupt that interrupted kernel mode?
*
- * We can do a kernel_fpu_begin/end() pair *ONLY* if that
+ * For now, on xsave platforms we will return interrupted
+ * kernel FPU as not-idle. TBD: As we use non-lazy FPU restore
+ * for xsave platforms, ideally we can change the return value
+ * to something like __thread_has_fpu(current). But we need to
+ * be careful of doing __thread_clear_has_fpu() before saving
+ * the FPU etc for supporting nested uses etc. For now, take
+ * the simple route!
+ *
+ * On others, we can do a kernel_fpu_begin/end() pair *ONLY* if that
* pair does nothing at all: the thread must not have fpu (so
* that we don't try to save the FPU state), and TS must
* be set (so that the clts/stts pair does nothing that is
*/
static inline bool interrupted_kernel_fpu_idle(void)
{
+ if (use_xsave())
+ return 0;
+
return !__thread_has_fpu(current) &&
(read_cr0() & X86_CR0_TS);
}
__save_init_fpu(me);
__thread_clear_has_fpu(me);
/* We do 'stts()' in kernel_fpu_end() */
- } else {
+ } else if (!use_xsave()) {
this_cpu_write(fpu_owner_task, NULL);
clts();
}
void kernel_fpu_end(void)
{
- stts();
+ if (use_xsave())
+ math_state_restore();
+ else
+ stts();
preempt_enable();
}
EXPORT_SYMBOL(kernel_fpu_end);
{
int ret;
- unlazy_fpu(src);
-
*dst = *src;
if (fpu_allocated(&src->thread.fpu)) {
memset(&dst->thread.fpu, 0, sizeof(dst->thread.fpu));
ret = fpu_alloc(&dst->thread.fpu);
if (ret)
return ret;
- fpu_copy(&dst->thread.fpu, &src->thread.fpu);
+ fpu_copy(dst, src);
}
return 0;
}
flush_ptrace_hw_breakpoint(tsk);
memset(tsk->thread.tls_array, 0, sizeof(tsk->thread.tls_array));
- drop_fpu(tsk);
+ drop_init_fpu(tsk);
+ /*
+ * Free the FPU state for non xsave platforms. They get reallocated
+ * lazily at the first use.
+ */
+ if (!use_xsave())
+ free_thread_xstate(tsk);
}
static void hard_disable_TSC(void)
regs->cs = __USER_CS;
regs->ip = new_ip;
regs->sp = new_sp;
- /*
- * Free the old FP and other extended state
- */
- free_thread_xstate(current);
}
EXPORT_SYMBOL_GPL(start_thread);
regs->cs = _cs;
regs->ss = _ss;
regs->flags = X86_EFLAGS_IF;
- /*
- * Free the old FP and other extended state
- */
- free_thread_xstate(current);
}
void
}
__thread_fpu_begin(tsk);
+
/*
* Paranoid restore. send a SIGSEGV if we fail to restore the state.
*/
if (unlikely(restore_fpu_checking(tsk))) {
- __thread_fpu_end(tsk);
+ drop_init_fpu(tsk);
force_sig(SIGSEGV, tsk);
return;
}
dotraplinkage void __kprobes
do_device_not_available(struct pt_regs *regs, long error_code)
{
+ BUG_ON(use_xsave());
+
#ifdef CONFIG_MATH_EMULATION
if (read_cr0() & X86_CR0_EM) {
struct math_emu_info info = { };
/*
* Represents init state for the supported extended state.
*/
-static struct xsave_struct *init_xstate_buf;
+struct xsave_struct *init_xstate_buf;
static struct _fpx_sw_bytes fx_sw_reserved, fx_sw_reserved_ia32;
static unsigned int *xstate_offsets, *xstate_sizes, xstate_features;
if (use_fxsr() && save_xstate_epilog(buf_fx, ia32_fxstate))
return -1;
- drop_fpu(tsk); /* trigger finit */
+ drop_init_fpu(tsk); /* trigger finit */
return 0;
}
config_enabled(CONFIG_IA32_EMULATION));
if (!buf) {
- drop_fpu(tsk);
+ drop_init_fpu(tsk);
return 0;
}
*/
struct xsave_struct *xsave = &tsk->thread.fpu.state->xsave;
struct user_i387_ia32_struct env;
+ int err = 0;
+ /*
+ * Drop the current fpu which clears used_math(). This ensures
+ * that any context-switch during the copy of the new state,
+ * avoids the intermediate state from getting restored/saved.
+ * Thus avoiding the new restored state from getting corrupted.
+ * We will be ready to restore/save the state only after
+ * set_used_math() is again set.
+ */
drop_fpu(tsk);
if (__copy_from_user(xsave, buf_fx, state_size) ||
- __copy_from_user(&env, buf, sizeof(env)))
- return -1;
+ __copy_from_user(&env, buf, sizeof(env))) {
+ err = -1;
+ } else {
+ sanitize_restored_xstate(tsk, &env, xstate_bv, fx_only);
+ set_used_math();
+ }
- sanitize_restored_xstate(tsk, &env, xstate_bv, fx_only);
- set_used_math();
+ if (use_xsave())
+ math_state_restore();
+
+ return err;
} else {
/*
* For 64-bit frames and 32-bit fsave frames, restore the user
*/
user_fpu_begin();
if (restore_user_xstate(buf_fx, xstate_bv, fx_only)) {
- drop_fpu(tsk);
+ drop_init_fpu(tsk);
return -1;
}
}
*/
static inline void xstate_enable(void)
{
+ clts();
set_in_cr4(X86_CR4_OSXSAVE);
xsetbv(XCR_XFEATURE_ENABLED_MASK, pcntxt_mask);
}
+/*
+ * This is same as math_state_restore(). But use_xsave() is not yet
+ * patched to use math_state_restore().
+ */
+static inline void init_restore_xstate(void)
+{
+ init_fpu(current);
+ __thread_fpu_begin(current);
+ xrstor_state(init_xstate_buf, -1);
+}
+
+static inline void xstate_enable_ap(void)
+{
+ xstate_enable();
+ init_restore_xstate();
+}
+
/*
* Record the offsets and sizes of different state managed by the xsave
* memory layout.
__alignof__(struct xsave_struct));
init_xstate_buf->i387.mxcsr = MXCSR_DEFAULT;
- clts();
/*
* Init all the features state with header_bv being 0x0
*/
* of any feature which is not represented by all zero's.
*/
xsave_state(init_xstate_buf, -1);
- stts();
}
/*
pr_info("enabled xstate_bv 0x%llx, cntxt size 0x%x\n",
pcntxt_mask, xstate_size);
+
+ current->thread.fpu.state =
+ alloc_bootmem_align(xstate_size, __alignof__(struct xsave_struct));
+ init_restore_xstate();
}
/*
return;
this_func = next_func;
- next_func = xstate_enable;
+ next_func = xstate_enable_ap;
this_func();
}
projects / linux-beck.git / commitdiff