Re: [patch 2/2] x86, fpu: lazy allocation of FPU area - v4

Bastien ROUCARIES
2008-03-06T12:36:47Z

Le mercredi 5 mars 2008, Suresh Siddha a écrit :
> Only allocate the FPU area when the application actually uses FPU, i.e., in
> the first lazy FPU trap. This could save memory for non-fpu using apps.
>
> Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
> Cc: Arjan van de Ven <arjan@linux.intel.com>
> ---
> v4: Handles the kmem_cache_alloc() failures.
> v3: Fixed the non-atomic calling sequence in atomic context.
> v2: Ported to x86.git#testing with some name changes.
> ---
>
> Index: linux-2.6-x86/arch/x86/kernel/i387.c
> ===================================================================
> --- linux-2.6-x86.orig/arch/x86/kernel/i387.c 2008-03-04 15:31:56.000000000
> -0800 +++ linux-2.6-x86/arch/x86/kernel/i387.c 2008-03-04
> 15:31:57.000000000 -0800 @@ -9,7 +9,6 @@
> #include <linux/sched.h>
> #include <linux/module.h>
> #include <linux/regset.h>
> -#include <linux/bootmem.h>
> #include <asm/processor.h>
> #include <asm/i387.h>
> #include <asm/math_emu.h>
> @@ -67,7 +66,6 @@
> else
> xstate_size = sizeof(struct i387_fsave_struct);
> #endif
> - init_task.thread.xstate = alloc_bootmem(xstate_size);
> }
>
> #ifdef CONFIG_X86_64
> @@ -97,12 +95,22 @@
> * value at reset if we support XMM instructions and then
> * remeber the current task has used the FPU.
> */
> -void init_fpu(struct task_struct *tsk)
> +int init_fpu(struct task_struct *tsk)
> {
> if (tsk_used_math(tsk)) {
> if (tsk == current)
> unlazy_fpu(tsk);
> - return;
> + return 0;
> + }
> +
> + /*
> + * Memory allocation at the first usage of the FPU and other state.
> + */
> + if (!tsk->thread.xstate) {
> + tsk->thread.xstate = kmem_cache_alloc(task_xstate_cachep,
> + GFP_KERNEL);
> + if (!tsk->thread.xstate)
> + return -ENOMEM;
> }
>
> if (cpu_has_fxsr) {
> @@ -124,6 +132,7 @@
> * Only the device not available exception or ptrace can call init_fpu.
> */
> set_stopped_child_used_math(tsk);
> + return 0;
> }
>
> int fpregs_active(struct task_struct *target, const struct user_regset
> *regset) @@ -140,10 +149,14 @@
> unsigned int pos, unsigned int count,
> void *kbuf, void __user *ubuf)
> {
> + int ret;
> +
> if (!cpu_has_fxsr)
> return -ENODEV;
>
> - init_fpu(target);
> + ret = init_fpu(target);
> + if (ret)
> + return ret;
>
> return user_regset_copyout(&pos, &count, &kbuf, &ubuf,
> &target->thread.xstate->fxsave, 0, -1);
> @@ -158,7 +171,10 @@
> if (!cpu_has_fxsr)
> return -ENODEV;
>
> - init_fpu(target);
> + ret = init_fpu(target);
> + if (ret)
> + return ret;
> +
> set_stopped_child_used_math(target);
>
> ret = user_regset_copyin(&pos, &count, &kbuf, &ubuf,
> @@ -314,11 +330,14 @@
> void *kbuf, void __user *ubuf)
> {
> struct user_i387_ia32_struct env;
> + int ret;
>
> if (!HAVE_HWFP)
> return fpregs_soft_get(target, regset, pos, count, kbuf, ubuf);
>
> - init_fpu(target);
> + ret = init_fpu(target);
> + if (ret)
> + return ret;
>
> if (!cpu_has_fxsr)
> return user_regset_copyout(&pos, &count, &kbuf, &ubuf,
> @@ -343,7 +362,10 @@
> if (!HAVE_HWFP)
> return fpregs_soft_set(target, regset, pos, count, kbuf, ubuf);
>
> - init_fpu(target);
> + ret = init_fpu(target);
> + if (ret)
> + return ret;
> +
> set_stopped_child_used_math(target);
>
> if (!cpu_has_fxsr)
> Index: linux-2.6-x86/arch/x86/kernel/process.c
> ===================================================================
> --- linux-2.6-x86.orig/arch/x86/kernel/process.c 2008-03-04
> 15:31:56.000000000 -0800 +++
> linux-2.6-x86/arch/x86/kernel/process.c 2008-03-04 15:32:23.000000000 -0800
> @@ -5,24 +5,34 @@
> #include <linux/slab.h>
> #include <linux/sched.h>
>
> -static struct kmem_cache *task_xstate_cachep;
> +struct kmem_cache *task_xstate_cachep;
>
> int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src)
> {
> *dst = *src;
> - dst->thread.xstate = kmem_cache_alloc(task_xstate_cachep, GFP_KERNEL);
> - if (!dst->thread.xstate)
> - return -ENOMEM;
> - WARN_ON((unsigned long)dst->thread.xstate & 15);
> - memcpy(dst->thread.xstate, src->thread.xstate, xstate_size);
> + if (src->thread.xstate) {
> + dst->thread.xstate = kmem_cache_alloc(task_xstate_cachep,
> + GFP_KERNEL);
> + if (!dst->thread.xstate)
> + return -ENOMEM;
> + WARN_ON((unsigned long)dst->thread.xstate & 15);
> + memcpy(dst->thread.xstate, src->thread.xstate, xstate_size);
> + }
> return 0;
> }
>
> -void free_thread_info(struct thread_info *ti)
> +void free_thread_xstate(struct task_struct *tsk)
> {
> - kmem_cache_free(task_xstate_cachep, ti->task->thread.xstate);
> - ti->task->thread.xstate = NULL;
> + if (tsk->thread.xstate) {
> + kmem_cache_free(task_xstate_cachep, tsk->thread.xstate);
> + tsk->thread.xstate = NULL;
> + }
> +}
> +
>
> +void free_thread_info(struct thread_info *ti)
> +{
> + free_thread_xstate(ti->task);
> free_pages((unsigned long)(ti), get_order(THREAD_SIZE));
> }
>
> Index: linux-2.6-x86/include/asm-x86/processor.h
> ===================================================================
> --- linux-2.6-x86.orig/include/asm-x86/processor.h 2008-03-04
> 15:31:56.000000000 -0800 +++
> linux-2.6-x86/include/asm-x86/processor.h 2008-03-04 15:31:57.000000000
> -0800 @@ -354,6 +354,8 @@
>
> extern void print_cpu_info(struct cpuinfo_x86 *);
> extern unsigned int xstate_size;
> +extern void free_thread_xstate(struct task_struct *);
> +extern struct kmem_cache *task_xstate_cachep;
> extern void init_scattered_cpuid_features(struct cpuinfo_x86 *c);
> extern unsigned int init_intel_cacheinfo(struct cpuinfo_x86 *c);
> extern unsigned short num_cache_leaves;
> Index: linux-2.6-x86/arch/x86/kernel/process_32.c
> ===================================================================
> --- linux-2.6-x86.orig/arch/x86/kernel/process_32.c 2008-03-04
> 15:31:56.000000000 -0800 +++
> linux-2.6-x86/arch/x86/kernel/process_32.c 2008-03-04 15:31:57.000000000
> -0800 @@ -524,6 +524,10 @@
> 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);
>
> Index: linux-2.6-x86/arch/x86/kernel/process_64.c
> ===================================================================
> --- linux-2.6-x86.orig/arch/x86/kernel/process_64.c 2008-03-04
> 15:31:56.000000000 -0800 +++
> linux-2.6-x86/arch/x86/kernel/process_64.c 2008-03-04 15:31:57.000000000
> -0800 @@ -552,6 +552,10 @@
> regs->ss = __USER_DS;
> regs->flags = 0x200;
> set_fs(USER_DS);
> + /*
> + * Free the old FP and other extended state
> + */
> + free_thread_xstate(current);
> }
> EXPORT_SYMBOL_GPL(start_thread);
>
> Index: linux-2.6-x86/arch/x86/kernel/traps_32.c
> ===================================================================
> --- linux-2.6-x86.orig/arch/x86/kernel/traps_32.c 2008-03-04
> 15:31:56.000000000 -0800 +++
> linux-2.6-x86/arch/x86/kernel/traps_32.c 2008-03-04 15:31:57.000000000
> -0800 @@ -1168,9 +1168,23 @@
> struct thread_info *thread = current_thread_info();
> struct task_struct *tsk = thread->task;
>
> + if (!tsk_used_math(tsk)) {
> +#ifdef CONFIG_PREEMPT
> + local_irq_enable();
> +#endif
> + /*
> + * does a slab alloc which can sleep
> + */
> + if (init_fpu(tsk)) {
> + force_sig(SIGSEGV, tsk);

May be SIGBUS will be better here?

> + return;
> + }
> +#ifdef CONFIG_PREEMPT
> + local_irq_disable();
> +#endif
> + }
> +
> clts(); /* Allow maths ops (or we recurse) */
> - if (!tsk_used_math(tsk))
> - init_fpu(tsk);
> restore_fpu(tsk);
> thread->status |= TS_USEDFPU; /* So we fnsave on switch_to() */
> tsk->fpu_counter++;
> Index: linux-2.6-x86/arch/x86/kernel/traps_64.c
> ===================================================================
> --- linux-2.6-x86.orig/arch/x86/kernel/traps_64.c 2008-03-04
> 15:31:56.000000000 -0800 +++
> linux-2.6-x86/arch/x86/kernel/traps_64.c 2008-03-04 15:31:57.000000000
> -0800 @@ -1117,10 +1117,15 @@
> asmlinkage void math_state_restore(void)
> {
> struct task_struct *me = current;
> - clts(); /* Allow maths ops (or we recurse) */
>
> - if (!used_math())
> - init_fpu(me);
> + if (!used_math()) {
> + if (init_fpu(me)) {
> + force_sig(SIGSEGV, me);
> + return;
> + }
> + }
> +
> + clts(); /* Allow maths ops (or we recurse) */
> restore_fpu_checking(&me->thread.xstate->fxsave);
> task_thread_info(me)->status |= TS_USEDFPU;
> me->fpu_counter++;
> Index: linux-2.6-x86/include/asm-x86/i387.h
> ===================================================================
> --- linux-2.6-x86.orig/include/asm-x86/i387.h 2008-03-04 15:31:56.000000000
> -0800 +++ linux-2.6-x86/include/asm-x86/i387.h 2008-03-04
> 15:31:57.000000000 -0800 @@ -21,7 +21,7 @@
>
> extern void fpu_init(void);
> extern void mxcsr_feature_mask_init(void);
> -extern void init_fpu(struct task_struct *child);
> +extern int init_fpu(struct task_struct *child);
> extern asmlinkage void math_state_restore(void);
> extern void init_thread_xstate(void);

Regards
--

"ROUCARIES Bastien"