x86/fpu: Simplify and speed up fpu__copy()

[people/arne_f/kernel.git] / arch / x86 / kernel / fpu / core.c

/*
 *  Copyright (C) 1994 Linus Torvalds
 *
 *  Pentium III FXSR, SSE support
 *  General FPU state handling cleanups
 *      Gareth Hughes <gareth@valinux.com>, May 2000
 */
#include <asm/fpu/internal.h>
#include <asm/fpu/regset.h>
#include <asm/fpu/signal.h>
#include <asm/fpu/types.h>
#include <asm/traps.h>

#include <linux/hardirq.h>
#include <linux/pkeys.h>

#define CREATE_TRACE_POINTS
#include <asm/trace/fpu.h>

/*
 * Represents the initial FPU state. It's mostly (but not completely) zeroes,
 * depending on the FPU hardware format:
 */
union fpregs_state init_fpstate __read_mostly;

/*
 * 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
 */
static DEFINE_PER_CPU(bool, in_kernel_fpu);

/*
 * Track which context is using the FPU on the CPU:
 */
DEFINE_PER_CPU(struct fpu *, fpu_fpregs_owner_ctx);

static void kernel_fpu_disable(void)
{
        WARN_ON_FPU(this_cpu_read(in_kernel_fpu));
        this_cpu_write(in_kernel_fpu, true);
}

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

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

static bool interrupted_kernel_fpu_idle(void)
{
        return !kernel_fpu_disabled();
}

/*
 * 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.
 */
static bool interrupted_user_mode(void)
{
        struct pt_regs *regs = get_irq_regs();
        return regs && user_mode(regs);
}

/*
 * 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);

void __kernel_fpu_begin(void)
{
        struct fpu *fpu = &current->thread.fpu;

        WARN_ON_FPU(!irq_fpu_usable());

        kernel_fpu_disable();

        if (fpu->initialized) {
                /*
                 * Ignore return value -- we don't care if reg state
                 * is clobbered.
                 */
                copy_fpregs_to_fpstate(fpu);
        } else {
                __cpu_invalidate_fpregs_state();
        }
}
EXPORT_SYMBOL(__kernel_fpu_begin);

void __kernel_fpu_end(void)
{
        struct fpu *fpu = &current->thread.fpu;

        if (fpu->initialized)
                copy_kernel_to_fpregs(&fpu->state);

        kernel_fpu_enable();
}
EXPORT_SYMBOL(__kernel_fpu_end);

void kernel_fpu_begin(void)
{
        preempt_disable();
        __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);

/*
 * Save the FPU state (mark it for reload if necessary):
 *
 * This only ever gets called for the current task.
 */
void fpu__save(struct fpu *fpu)
{
        WARN_ON_FPU(fpu != &current->thread.fpu);

        preempt_disable();
        trace_x86_fpu_before_save(fpu);
        if (fpu->initialized) {
                if (!copy_fpregs_to_fpstate(fpu)) {
                        copy_kernel_to_fpregs(&fpu->state);
                }
        }
        trace_x86_fpu_after_save(fpu);
        preempt_enable();
}
EXPORT_SYMBOL_GPL(fpu__save);

/*
 * Legacy x87 fpstate state init:
 */
static inline void fpstate_init_fstate(struct fregs_state *fp)
{
        fp->cwd = 0xffff037fu;
        fp->swd = 0xffff0000u;
        fp->twd = 0xffffffffu;
        fp->fos = 0xffff0000u;
}

void fpstate_init(union fpregs_state *state)
{
        if (!static_cpu_has(X86_FEATURE_FPU)) {
                fpstate_init_soft(&state->soft);
                return;
        }

        memset(state, 0, fpu_kernel_xstate_size);

        if (static_cpu_has(X86_FEATURE_XSAVES))
                fpstate_init_xstate(&state->xsave);
        if (static_cpu_has(X86_FEATURE_FXSR))
                fpstate_init_fxstate(&state->fxsave);
        else
                fpstate_init_fstate(&state->fsave);
}
EXPORT_SYMBOL_GPL(fpstate_init);

int fpu__copy(struct fpu *dst_fpu, struct fpu *src_fpu)
{
        dst_fpu->last_cpu = -1;

        if (!src_fpu->initialized || !static_cpu_has(X86_FEATURE_FPU))
                return 0;

        WARN_ON_FPU(src_fpu != &current->thread.fpu);

        /*
         * Don't let 'init optimized' areas of the XSAVE area
         * leak into the child task:
         */
        memset(&dst_fpu->state.xsave, 0, fpu_kernel_xstate_size);

        /*
         * Save current FPU registers directly into the child
         * FPU context, without any memory-to-memory copying.
         *
         * ( The function 'fails' in the FNSAVE case, which destroys
         *   register contents so we have to copy them back. )
         */
        if (!copy_fpregs_to_fpstate(dst_fpu)) {
                memcpy(&src_fpu->state, &dst_fpu->state, fpu_kernel_xstate_size);
                copy_kernel_to_fpregs(&src_fpu->state);
        }

        trace_x86_fpu_copy_src(src_fpu);
        trace_x86_fpu_copy_dst(dst_fpu);

        return 0;
}

/*
 * Activate the current task's in-memory FPU context,
 * if it has not been used before:
 */
void fpu__activate_curr(struct fpu *fpu)
{
        WARN_ON_FPU(fpu != &current->thread.fpu);

        if (!fpu->initialized) {
                fpstate_init(&fpu->state);
                trace_x86_fpu_init_state(fpu);

                trace_x86_fpu_activate_state(fpu);
                /* Safe to do for the current task: */
                fpu->initialized = 1;
        }
}
EXPORT_SYMBOL_GPL(fpu__activate_curr);

/*
 * This function must be called before we read a task's fpstate.
 *
 * There's two cases where this gets called:
 *
 * - for the current task (when coredumping), in which case we have
 *   to save the latest FPU registers into the fpstate,
 *
 * - or it's called for stopped tasks (ptrace), in which case the
 *   registers were already saved by the context-switch code when
 *   the task scheduled out - we only have to initialize the registers
 *   if they've never been initialized.
 *
 * If the task has used the FPU before then save it.
 */
void fpu__activate_fpstate_read(struct fpu *fpu)
{
        if (fpu == &current->thread.fpu) {
                fpu__save(fpu);
        } else {
                if (!fpu->initialized) {
                        fpstate_init(&fpu->state);
                        trace_x86_fpu_init_state(fpu);

                        trace_x86_fpu_activate_state(fpu);
                        /* Safe to do for current and for stopped child tasks: */
                        fpu->initialized = 1;
                }
        }
}

/*
 * This function must be called before we write a task's fpstate.
 *
 * If the task has used the FPU before then invalidate any cached FPU registers.
 * If the task has not used the FPU before then initialize its fpstate.
 *
 * After this function call, after registers in the fpstate are
 * modified and the child task has woken up, the child task will
 * restore the modified FPU state from the modified context. If we
 * didn't clear its cached status here then the cached in-registers
 * state pending on its former CPU could be restored, corrupting
 * the modifications.
 */
void fpu__activate_fpstate_write(struct fpu *fpu)
{
        /*
         * Only stopped child tasks can be used to modify the FPU
         * state in the fpstate buffer:
         */
        WARN_ON_FPU(fpu == &current->thread.fpu);

        if (fpu->initialized) {
                /* Invalidate any cached state: */
                __fpu_invalidate_fpregs_state(fpu);
        } else {
                fpstate_init(&fpu->state);
                trace_x86_fpu_init_state(fpu);

                trace_x86_fpu_activate_state(fpu);
                /* Safe to do for stopped child tasks: */
                fpu->initialized = 1;
        }
}

/*
 * 'fpu__restore()' is called to copy FPU registers from
 * the FPU fpstate to the live hw registers and to activate
 * access to the hardware registers, so that FPU instructions
 * can be used afterwards.
 *
 * Must be called with kernel preemption disabled (for example
 * with local interrupts disabled, as it is in the case of
 * do_device_not_available()).
 */
void fpu__restore(struct fpu *fpu)
{
        fpu__activate_curr(fpu);

        /* Avoid __kernel_fpu_begin() right after fpregs_activate() */
        kernel_fpu_disable();
        trace_x86_fpu_before_restore(fpu);
        fpregs_activate(fpu);
        copy_kernel_to_fpregs(&fpu->state);
        trace_x86_fpu_after_restore(fpu);
        kernel_fpu_enable();
}
EXPORT_SYMBOL_GPL(fpu__restore);

/*
 * Drops current FPU state: deactivates the fpregs and
 * the fpstate. NOTE: it still leaves previous contents
 * in the fpregs in the eager-FPU case.
 *
 * This function can be used in cases where we know that
 * a state-restore is coming: either an explicit one,
 * or a reschedule.
 */
void fpu__drop(struct fpu *fpu)
{
        preempt_disable();

        if (fpu == &current->thread.fpu) {
                if (fpu->initialized) {
                        /* Ignore delayed exceptions from user space */
                        asm volatile("1: fwait\n"
                                     "2:\n"
                                     _ASM_EXTABLE(1b, 2b));
                        fpregs_deactivate(fpu);
                }
        }

        fpu->initialized = 0;

        trace_x86_fpu_dropped(fpu);

        preempt_enable();
}

/*
 * Clear FPU registers by setting them up from
 * the init fpstate:
 */
static inline void copy_init_fpstate_to_fpregs(void)
{
        if (use_xsave())
                copy_kernel_to_xregs(&init_fpstate.xsave, -1);
        else if (static_cpu_has(X86_FEATURE_FXSR))
                copy_kernel_to_fxregs(&init_fpstate.fxsave);
        else
                copy_kernel_to_fregs(&init_fpstate.fsave);

        if (boot_cpu_has(X86_FEATURE_OSPKE))
                copy_init_pkru_to_fpregs();
}

/*
 * Clear the FPU state back to init state.
 *
 * Called by sys_execve(), by the signal handler code and by various
 * error paths.
 */
void fpu__clear(struct fpu *fpu)
{
        WARN_ON_FPU(fpu != &current->thread.fpu); /* Almost certainly an anomaly */

        fpu__drop(fpu);

        /*
         * Make sure fpstate is cleared and initialized.
         */
        if (static_cpu_has(X86_FEATURE_FPU)) {
                preempt_disable();
                fpu__activate_curr(fpu);
                user_fpu_begin();
                copy_init_fpstate_to_fpregs();
                preempt_enable();
        }
}

/*
 * x87 math exception handling:
 */

int fpu__exception_code(struct fpu *fpu, int trap_nr)
{
        int err;

        if (trap_nr == X86_TRAP_MF) {
                unsigned short cwd, swd;
                /*
                 * (~cwd & swd) will mask out exceptions that are not set to unmasked
                 * status.  0x3f is the exception bits in these regs, 0x200 is the
                 * C1 reg you need in case of a stack fault, 0x040 is the stack
                 * fault bit.  We should only be taking one exception at a time,
                 * so if this combination doesn't produce any single exception,
                 * then we have a bad program that isn't synchronizing its FPU usage
                 * and it will suffer the consequences since we won't be able to
                 * fully reproduce the context of the exception.
                 */
                if (boot_cpu_has(X86_FEATURE_FXSR)) {
                        cwd = fpu->state.fxsave.cwd;
                        swd = fpu->state.fxsave.swd;
                } else {
                        cwd = (unsigned short)fpu->state.fsave.cwd;
                        swd = (unsigned short)fpu->state.fsave.swd;
                }

                err = swd & ~cwd;
        } else {
                /*
                 * The SIMD FPU exceptions are handled a little differently, as there
                 * is only a single status/control register.  Thus, to determine which
                 * unmasked exception was caught we must mask the exception mask bits
                 * at 0x1f80, and then use these to mask the exception bits at 0x3f.
                 */
                unsigned short mxcsr = MXCSR_DEFAULT;

                if (boot_cpu_has(X86_FEATURE_XMM))
                        mxcsr = fpu->state.fxsave.mxcsr;

                err = ~(mxcsr >> 7) & mxcsr;
        }

        if (err & 0x001) {      /* Invalid op */
                /*
                 * swd & 0x240 == 0x040: Stack Underflow
                 * swd & 0x240 == 0x240: Stack Overflow
                 * User must clear the SF bit (0x40) if set
                 */
                return FPE_FLTINV;
        } else if (err & 0x004) { /* Divide by Zero */
                return FPE_FLTDIV;
        } else if (err & 0x008) { /* Overflow */
                return FPE_FLTOVF;
        } else if (err & 0x012) { /* Denormal, Underflow */
                return FPE_FLTUND;
        } else if (err & 0x020) { /* Precision */
                return FPE_FLTRES;
        }

        /*
         * If we're using IRQ 13, or supposedly even some trap
         * X86_TRAP_MF implementations, it's possible
         * we get a spurious trap, which is not an error.
         */
        return 0;
}