core.c 16.9 KB
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/*
 *  Copyright (C) 1994 Linus Torvalds
 *
 *  Pentium III FXSR, SSE support
 *  General FPU state handling cleanups
 *	Gareth Hughes <gareth@valinux.com>, May 2000
 */
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#include <asm/fpu/internal.h>
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#include <linux/hardirq.h>
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/*
 * Track whether the kernel is using the FPU state
 * currently.
 *
 * This flag is used:
 *
 *   - by IRQ context code to potentially use the FPU
 *     if it's unused.
 *
 *   - to debug kernel_fpu_begin()/end() correctness
 */
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static DEFINE_PER_CPU(bool, in_kernel_fpu);

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/*
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 * Track which context is using the FPU on the CPU:
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 */
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DEFINE_PER_CPU(struct fpu *, fpu_fpregs_owner_ctx);
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static void kernel_fpu_disable(void)
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{
	WARN_ON(this_cpu_read(in_kernel_fpu));
	this_cpu_write(in_kernel_fpu, true);
}

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static void kernel_fpu_enable(void)
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{
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	WARN_ON_ONCE(!this_cpu_read(in_kernel_fpu));
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	this_cpu_write(in_kernel_fpu, false);
}

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static bool kernel_fpu_disabled(void)
{
	return this_cpu_read(in_kernel_fpu);
}

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/*
 * Were we in an interrupt that interrupted kernel mode?
 *
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 * On others, we can do a kernel_fpu_begin/end() pair *ONLY* if that
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 * 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
 * visible in the interrupted kernel thread).
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 *
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 * Except for the eagerfpu case when we return true; in the likely case
 * the thread has FPU but we are not going to set/clear TS.
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 */
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static bool interrupted_kernel_fpu_idle(void)
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{
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	if (kernel_fpu_disabled())
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		return false;

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	if (use_eager_fpu())
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		return true;
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	return !current->thread.fpu.fpregs_active && (read_cr0() & X86_CR0_TS);
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}

/*
 * Were we in user mode (or vm86 mode) when we were
 * interrupted?
 *
 * Doing kernel_fpu_begin/end() is ok if we are running
 * in an interrupt context from user mode - we'll just
 * save the FPU state as required.
 */
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static bool interrupted_user_mode(void)
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{
	struct pt_regs *regs = get_irq_regs();
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	return regs && user_mode(regs);
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}

/*
 * Can we use the FPU in kernel mode with the
 * whole "kernel_fpu_begin/end()" sequence?
 *
 * It's always ok in process context (ie "not interrupt")
 * but it is sometimes ok even from an irq.
 */
bool irq_fpu_usable(void)
{
	return !in_interrupt() ||
		interrupted_user_mode() ||
		interrupted_kernel_fpu_idle();
}
EXPORT_SYMBOL(irq_fpu_usable);

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void __kernel_fpu_begin(void)
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{
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	struct fpu *fpu = &current->thread.fpu;
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	kernel_fpu_disable();
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	if (fpu->fpregs_active) {
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		copy_fpregs_to_fpstate(fpu);
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	} else {
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		this_cpu_write(fpu_fpregs_owner_ctx, NULL);
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		if (!use_eager_fpu())
			clts();
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	}
}
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EXPORT_SYMBOL(__kernel_fpu_begin);
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void __kernel_fpu_end(void)
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{
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	struct fpu *fpu = &current->thread.fpu;
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	if (fpu->fpregs_active) {
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		if (WARN_ON(restore_fpu_checking(fpu)))
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			fpu_reset_state(fpu);
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	} else if (!use_eager_fpu()) {
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		stts();
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	}
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	kernel_fpu_enable();
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}
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EXPORT_SYMBOL(__kernel_fpu_end);
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void kernel_fpu_begin(void)
{
	preempt_disable();
	WARN_ON_ONCE(!irq_fpu_usable());
	__kernel_fpu_begin();
}
EXPORT_SYMBOL_GPL(kernel_fpu_begin);

void kernel_fpu_end(void)
{
	__kernel_fpu_end();
	preempt_enable();
}
EXPORT_SYMBOL_GPL(kernel_fpu_end);

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/*
 * CR0::TS save/restore functions:
 */
int irq_ts_save(void)
{
	/*
	 * If in process context and not atomic, we can take a spurious DNA fault.
	 * Otherwise, doing clts() in process context requires disabling preemption
	 * or some heavy lifting like kernel_fpu_begin()
	 */
	if (!in_atomic())
		return 0;

	if (read_cr0() & X86_CR0_TS) {
		clts();
		return 1;
	}

	return 0;
}
EXPORT_SYMBOL_GPL(irq_ts_save);

void irq_ts_restore(int TS_state)
{
	if (TS_state)
		stts();
}
EXPORT_SYMBOL_GPL(irq_ts_restore);

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static void __save_fpu(struct fpu *fpu)
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{
	if (use_xsave()) {
		if (unlikely(system_state == SYSTEM_BOOTING))
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			xsave_state_booting(&fpu->state.xsave);
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		else
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			xsave_state(&fpu->state.xsave);
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	} else {
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		fpu_fxsave(fpu);
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	}
}

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/*
 * Save the FPU state (initialize it if necessary):
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 *
 * This only ever gets called for the current task.
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 */
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void fpu__save(struct fpu *fpu)
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{
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	WARN_ON(fpu != &current->thread.fpu);
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	preempt_disable();
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	if (fpu->fpregs_active) {
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		if (use_eager_fpu()) {
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			__save_fpu(fpu);
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		} else {
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			copy_fpregs_to_fpstate(fpu);
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			fpregs_deactivate(fpu);
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		}
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	}
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	preempt_enable();
}
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EXPORT_SYMBOL_GPL(fpu__save);
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void fpstate_init(struct fpu *fpu)
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{
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	if (!cpu_has_fpu) {
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		finit_soft_fpu(&fpu->state.soft);
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		return;
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	}

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	memset(&fpu->state, 0, xstate_size);
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	if (cpu_has_fxsr) {
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		fx_finit(&fpu->state.fxsave);
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	} else {
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		struct i387_fsave_struct *fp = &fpu->state.fsave;
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		fp->cwd = 0xffff037fu;
		fp->swd = 0xffff0000u;
		fp->twd = 0xffffffffu;
		fp->fos = 0xffff0000u;
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	}
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}
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EXPORT_SYMBOL_GPL(fpstate_init);
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/*
 * Copy the current task's FPU state to a new task's FPU context.
 *
 * In the 'eager' case we just save to the destination context.
 *
 * In the 'lazy' case we save to the source context, mark the FPU lazy
 * via stts() and copy the source context into the destination context.
 */
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static void fpu_copy(struct fpu *dst_fpu, struct fpu *src_fpu)
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{
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	WARN_ON(src_fpu != &current->thread.fpu);
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	if (use_eager_fpu()) {
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		memset(&dst_fpu->state.xsave, 0, xstate_size);
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		__save_fpu(dst_fpu);
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	} else {
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		fpu__save(src_fpu);
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		memcpy(&dst_fpu->state, &src_fpu->state, xstate_size);
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	}
}

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int fpu__copy(struct fpu *dst_fpu, struct fpu *src_fpu)
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{
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	dst_fpu->counter = 0;
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	dst_fpu->fpregs_active = 0;
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	dst_fpu->last_cpu = -1;
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	if (src_fpu->fpstate_active)
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		fpu_copy(dst_fpu, src_fpu);
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	return 0;
}

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/*
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 * Initialize the current task's in-memory FPU context:
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 */
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void fpstate_init_curr(struct fpu *fpu)
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{
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	WARN_ON_ONCE(fpu != &current->thread.fpu);
	WARN_ON_ONCE(fpu->fpstate_active);
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	fpstate_init(fpu);
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	/* Safe to do for the current task: */
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	fpu->fpstate_active = 1;
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}
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EXPORT_SYMBOL_GPL(fpstate_init_curr);
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/*
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 * This function is called before we modify a stopped child's
 * FPU state context.
 *
 * If the child has not used the FPU before then initialize its
 * FPU context.
 *
 * If the child has used the FPU before then unlazy it.
 *
 * [ After this function call, after the context is modified and
 *   the child task is woken up, the child task will restore
 *   the modified FPU state from the modified context. If we
 *   didn't clear its lazy status here then the lazy in-registers
 *   state pending on its former CPU could be restored, losing
 *   the modifications. ]
 *
 * This function is also called before we read a stopped child's
 * FPU state - to make sure it's modified.
 *
 * TODO: A future optimization would be to skip the unlazying in
 *       the read-only case, it's not strictly necessary for
 *       read-only access to the context.
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 */
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static int fpu__unlazy_stopped(struct fpu *child_fpu)
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{
	int ret;

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	if (WARN_ON_ONCE(child_fpu == &current->thread.fpu))
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		return -EINVAL;

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	if (child_fpu->fpstate_active) {
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		child_fpu->last_cpu = -1;
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		return 0;
	}

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	fpstate_init(child_fpu);
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	/* Safe to do for stopped child tasks: */
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	child_fpu->fpstate_active = 1;
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	return 0;
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}

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/*
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 * 'fpu__restore()' saves the current math information in the
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 * old math state array, and gets the new ones from the current task
 *
 * Careful.. There are problems with IBM-designed IRQ13 behaviour.
 * Don't touch unless you *really* know how it works.
 *
 * Must be called with kernel preemption disabled (eg with local
 * local interrupts as in the case of do_device_not_available).
 */
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void fpu__restore(void)
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{
	struct task_struct *tsk = current;
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	struct fpu *fpu = &tsk->thread.fpu;
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	if (!fpu->fpstate_active)
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		fpstate_init_curr(fpu);
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	/* Avoid __kernel_fpu_begin() right after fpregs_activate() */
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	kernel_fpu_disable();
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	fpregs_activate(fpu);
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	if (unlikely(restore_fpu_checking(fpu))) {
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		fpu_reset_state(fpu);
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		force_sig_info(SIGSEGV, SEND_SIG_PRIV, tsk);
	} else {
		tsk->thread.fpu.counter++;
	}
	kernel_fpu_enable();
}
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EXPORT_SYMBOL_GPL(fpu__restore);
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void fpu__clear(struct task_struct *tsk)
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{
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	struct fpu *fpu = &tsk->thread.fpu;

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	WARN_ON_ONCE(tsk != current); /* Almost certainly an anomaly */
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	if (!use_eager_fpu()) {
		/* FPU state will be reallocated lazily at the first use. */
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		drop_fpu(fpu);
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	} else {
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		if (!fpu->fpstate_active) {
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			fpstate_init_curr(fpu);
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			user_fpu_begin();
		}
		restore_init_xstate();
	}
}

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/*
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 * The xstateregs_active() routine is the same as the regset_fpregs_active() routine,
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 * as the "regset->n" for the xstate regset will be updated based on the feature
 * capabilites supported by the xsave.
 */
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int regset_fpregs_active(struct task_struct *target, const struct user_regset *regset)
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{
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	struct fpu *target_fpu = &target->thread.fpu;

	return target_fpu->fpstate_active ? regset->n : 0;
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}
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int regset_xregset_fpregs_active(struct task_struct *target, const struct user_regset *regset)
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{
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	struct fpu *target_fpu = &target->thread.fpu;

	return (cpu_has_fxsr && target_fpu->fpstate_active) ? regset->n : 0;
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}
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int xfpregs_get(struct task_struct *target, const struct user_regset *regset,
		unsigned int pos, unsigned int count,
		void *kbuf, void __user *ubuf)
{
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	struct fpu *fpu = &target->thread.fpu;
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	int ret;

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	if (!cpu_has_fxsr)
		return -ENODEV;

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	ret = fpu__unlazy_stopped(fpu);
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	if (ret)
		return ret;
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	sanitize_i387_state(target);

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	return user_regset_copyout(&pos, &count, &kbuf, &ubuf,
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				   &fpu->state.fxsave, 0, -1);
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}
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int xfpregs_set(struct task_struct *target, const struct user_regset *regset,
		unsigned int pos, unsigned int count,
		const void *kbuf, const void __user *ubuf)
{
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	struct fpu *fpu = &target->thread.fpu;
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	int ret;

	if (!cpu_has_fxsr)
		return -ENODEV;

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	ret = fpu__unlazy_stopped(fpu);
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	if (ret)
		return ret;

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	sanitize_i387_state(target);

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	ret = user_regset_copyin(&pos, &count, &kbuf, &ubuf,
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				 &fpu->state.fxsave, 0, -1);
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	/*
	 * mxcsr reserved bits must be masked to zero for security reasons.
	 */
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	fpu->state.fxsave.mxcsr &= mxcsr_feature_mask;
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	/*
	 * update the header bits in the xsave header, indicating the
	 * presence of FP and SSE state.
	 */
	if (cpu_has_xsave)
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		fpu->state.xsave.header.xfeatures |= XSTATE_FPSSE;
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	return ret;
}

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int xstateregs_get(struct task_struct *target, const struct user_regset *regset,
		unsigned int pos, unsigned int count,
		void *kbuf, void __user *ubuf)
{
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	struct fpu *fpu = &target->thread.fpu;
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	struct xsave_struct *xsave;
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	int ret;

	if (!cpu_has_xsave)
		return -ENODEV;

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	ret = fpu__unlazy_stopped(fpu);
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	if (ret)
		return ret;

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	xsave = &fpu->state.xsave;
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	/*
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	 * Copy the 48bytes defined by the software first into the xstate
	 * memory layout in the thread struct, so that we can copy the entire
	 * xstateregs to the user using one user_regset_copyout().
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	 */
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	memcpy(&xsave->i387.sw_reserved,
		xstate_fx_sw_bytes, sizeof(xstate_fx_sw_bytes));
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	/*
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	 * Copy the xstate memory layout.
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	 */
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	ret = user_regset_copyout(&pos, &count, &kbuf, &ubuf, xsave, 0, -1);
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	return ret;
}

int xstateregs_set(struct task_struct *target, const struct user_regset *regset,
		  unsigned int pos, unsigned int count,
		  const void *kbuf, const void __user *ubuf)
{
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	struct fpu *fpu = &target->thread.fpu;
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	struct xsave_struct *xsave;
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	int ret;

	if (!cpu_has_xsave)
		return -ENODEV;

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	ret = fpu__unlazy_stopped(fpu);
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	if (ret)
		return ret;

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	xsave = &fpu->state.xsave;
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	ret = user_regset_copyin(&pos, &count, &kbuf, &ubuf, xsave, 0, -1);
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	/*
	 * mxcsr reserved bits must be masked to zero for security reasons.
	 */
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	xsave->i387.mxcsr &= mxcsr_feature_mask;
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	xsave->header.xfeatures &= xfeatures_mask;
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	/*
	 * These bits must be zero.
	 */
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	memset(&xsave->header.reserved, 0, 48);
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	return ret;
}

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#if defined CONFIG_X86_32 || defined CONFIG_IA32_EMULATION
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/*
 * FPU tag word conversions.
 */

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static inline unsigned short twd_i387_to_fxsr(unsigned short twd)
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{
	unsigned int tmp; /* to avoid 16 bit prefixes in the code */
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	/* Transform each pair of bits into 01 (valid) or 00 (empty) */
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	tmp = ~twd;
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	tmp = (tmp | (tmp>>1)) & 0x5555; /* 0V0V0V0V0V0V0V0V */
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	/* and move the valid bits to the lower byte. */
	tmp = (tmp | (tmp >> 1)) & 0x3333; /* 00VV00VV00VV00VV */
	tmp = (tmp | (tmp >> 2)) & 0x0f0f; /* 0000VVVV0000VVVV */
	tmp = (tmp | (tmp >> 4)) & 0x00ff; /* 00000000VVVVVVVV */
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	return tmp;
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}

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#define FPREG_ADDR(f, n)	((void *)&(f)->st_space + (n) * 16)
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#define FP_EXP_TAG_VALID	0
#define FP_EXP_TAG_ZERO		1
#define FP_EXP_TAG_SPECIAL	2
#define FP_EXP_TAG_EMPTY	3

static inline u32 twd_fxsr_to_i387(struct i387_fxsave_struct *fxsave)
{
	struct _fpxreg *st;
	u32 tos = (fxsave->swd >> 11) & 7;
	u32 twd = (unsigned long) fxsave->twd;
	u32 tag;
	u32 ret = 0xffff0000u;
	int i;
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	for (i = 0; i < 8; i++, twd >>= 1) {
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		if (twd & 0x1) {
			st = FPREG_ADDR(fxsave, (i - tos) & 7);
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			switch (st->exponent & 0x7fff) {
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			case 0x7fff:
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				tag = FP_EXP_TAG_SPECIAL;
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				break;
			case 0x0000:
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				if (!st->significand[0] &&
				    !st->significand[1] &&
				    !st->significand[2] &&
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				    !st->significand[3])
					tag = FP_EXP_TAG_ZERO;
				else
					tag = FP_EXP_TAG_SPECIAL;
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				break;
			default:
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				if (st->significand[3] & 0x8000)
					tag = FP_EXP_TAG_VALID;
				else
					tag = FP_EXP_TAG_SPECIAL;
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				break;
			}
		} else {
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			tag = FP_EXP_TAG_EMPTY;
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		}
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		ret |= tag << (2 * i);
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	}
	return ret;
}

/*
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 * FXSR floating point environment conversions.
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 */

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void
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convert_from_fxsr(struct user_i387_ia32_struct *env, struct task_struct *tsk)
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{
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	struct i387_fxsave_struct *fxsave = &tsk->thread.fpu.state.fxsave;
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	struct _fpreg *to = (struct _fpreg *) &env->st_space[0];
	struct _fpxreg *from = (struct _fpxreg *) &fxsave->st_space[0];
	int i;
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	env->cwd = fxsave->cwd | 0xffff0000u;
	env->swd = fxsave->swd | 0xffff0000u;
	env->twd = twd_fxsr_to_i387(fxsave);

#ifdef CONFIG_X86_64
	env->fip = fxsave->rip;
	env->foo = fxsave->rdp;
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	/*
	 * should be actually ds/cs at fpu exception time, but
	 * that information is not available in 64bit mode.
	 */
	env->fcs = task_pt_regs(tsk)->cs;
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	if (tsk == current) {
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		savesegment(ds, env->fos);
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	} else {
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		env->fos = tsk->thread.ds;
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	}
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	env->fos |= 0xffff0000;
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#else
	env->fip = fxsave->fip;
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	env->fcs = (u16) fxsave->fcs | ((u32) fxsave->fop << 16);
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	env->foo = fxsave->foo;
	env->fos = fxsave->fos;
#endif
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	for (i = 0; i < 8; ++i)
		memcpy(&to[i], &from[i], sizeof(to[0]));
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}

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void convert_to_fxsr(struct task_struct *tsk,
		     const struct user_i387_ia32_struct *env)
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{
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	struct i387_fxsave_struct *fxsave = &tsk->thread.fpu.state.fxsave;
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	struct _fpreg *from = (struct _fpreg *) &env->st_space[0];
	struct _fpxreg *to = (struct _fpxreg *) &fxsave->st_space[0];
	int i;
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	fxsave->cwd = env->cwd;
	fxsave->swd = env->swd;
	fxsave->twd = twd_i387_to_fxsr(env->twd);
	fxsave->fop = (u16) ((u32) env->fcs >> 16);
#ifdef CONFIG_X86_64
	fxsave->rip = env->fip;
	fxsave->rdp = env->foo;
	/* cs and ds ignored */
#else
	fxsave->fip = env->fip;
	fxsave->fcs = (env->fcs & 0xffff);
	fxsave->foo = env->foo;
	fxsave->fos = env->fos;
#endif
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	for (i = 0; i < 8; ++i)
		memcpy(&to[i], &from[i], sizeof(from[0]));
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}

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int fpregs_get(struct task_struct *target, const struct user_regset *regset,
	       unsigned int pos, unsigned int count,
	       void *kbuf, void __user *ubuf)
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{
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	struct fpu *fpu = &target->thread.fpu;
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	struct user_i387_ia32_struct env;
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	int ret;
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	ret = fpu__unlazy_stopped(fpu);
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	if (ret)
		return ret;
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	if (!static_cpu_has(X86_FEATURE_FPU))
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		return fpregs_soft_get(target, regset, pos, count, kbuf, ubuf);

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	if (!cpu_has_fxsr)
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		return user_regset_copyout(&pos, &count, &kbuf, &ubuf,
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					   &fpu->state.fsave, 0,
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					   -1);
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	sanitize_i387_state(target);

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	if (kbuf && pos == 0 && count == sizeof(env)) {
		convert_from_fxsr(kbuf, target);
		return 0;
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	}
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	convert_from_fxsr(&env, target);
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	return user_regset_copyout(&pos, &count, &kbuf, &ubuf, &env, 0, -1);
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}

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int fpregs_set(struct task_struct *target, const struct user_regset *regset,
	       unsigned int pos, unsigned int count,
	       const void *kbuf, const void __user *ubuf)
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{
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	struct fpu *fpu = &target->thread.fpu;
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	struct user_i387_ia32_struct env;
	int ret;
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	ret = fpu__unlazy_stopped(fpu);
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	if (ret)
		return ret;

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	sanitize_i387_state(target);

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	if (!static_cpu_has(X86_FEATURE_FPU))
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		return fpregs_soft_set(target, regset, pos, count, kbuf, ubuf);

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	if (!cpu_has_fxsr)
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		return user_regset_copyin(&pos, &count, &kbuf, &ubuf,
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					  &fpu->state.fsave, 0,
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					  -1);
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	if (pos > 0 || count < sizeof(env))
		convert_from_fxsr(&env, target);

	ret = user_regset_copyin(&pos, &count, &kbuf, &ubuf, &env, 0, -1);
	if (!ret)
		convert_to_fxsr(target, &env);

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	/*
	 * update the header bit in the xsave header, indicating the
	 * presence of FP.
	 */
	if (cpu_has_xsave)
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		fpu->state.xsave.header.xfeatures |= XSTATE_FP;
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	return ret;
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}

/*
 * FPU state for core dumps.
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 * This is only used for a.out dumps now.
 * It is declared generically using elf_fpregset_t (which is
 * struct user_i387_struct) but is in fact only used for 32-bit
 * dumps, so on 64-bit it is really struct user_i387_ia32_struct.
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 */
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int dump_fpu(struct pt_regs *regs, struct user_i387_struct *ufpu)
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{
	struct task_struct *tsk = current;
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	struct fpu *fpu = &tsk->thread.fpu;
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	int fpvalid;
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	fpvalid = fpu->fpstate_active;
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	if (fpvalid)
		fpvalid = !fpregs_get(tsk, NULL,
				      0, sizeof(struct user_i387_ia32_struct),
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				      ufpu, NULL);
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	return fpvalid;
}
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EXPORT_SYMBOL(dump_fpu);
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#endif	/* CONFIG_X86_32 || CONFIG_IA32_EMULATION */