[deliverable/linux.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 <linux/hardirq.h>

/*
 * 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(this_cpu_read(in_kernel_fpu));
        this_cpu_write(in_kernel_fpu, true);
}

static void kernel_fpu_enable(void)
{
        WARN_ON_ONCE(!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);
}

/*
 * Were we in an interrupt that interrupted kernel mode?
 *
 * 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
 * visible in the interrupted kernel thread).
 *
 * 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.
 */
static bool interrupted_kernel_fpu_idle(void)
{
        if (kernel_fpu_disabled())
                return false;

        if (use_eager_fpu())
                return true;

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

/*
 * 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;

        kernel_fpu_disable();

        if (fpu->fpregs_active) {
                copy_fpregs_to_fpstate(fpu);
        } else {
                this_cpu_write(fpu_fpregs_owner_ctx, NULL);
                __fpregs_activate_hw();
        }
}
EXPORT_SYMBOL(__kernel_fpu_begin);

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

        if (fpu->fpregs_active) {
                if (WARN_ON(copy_fpstate_to_fpregs(fpu)))
                        fpu__clear(fpu);
        } else {
                __fpregs_deactivate_hw();
        }

        kernel_fpu_enable();
}
EXPORT_SYMBOL(__kernel_fpu_end);

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);

/*
 * 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);

/*
 * 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 != &current->thread.fpu);

        preempt_disable();
        if (fpu->fpregs_active) {
                if (!copy_fpregs_to_fpstate(fpu))
                        fpregs_deactivate(fpu);
        }
        preempt_enable();
}
EXPORT_SYMBOL_GPL(fpu__save);

void fpstate_init(struct fpu *fpu)
{
        if (!cpu_has_fpu) {
                finit_soft_fpu(&fpu->state.soft);
                return;
        }

        memset(&fpu->state, 0, xstate_size);

        if (cpu_has_fxsr) {
                fx_finit(&fpu->state.fxsave);
        } else {
                struct i387_fsave_struct *fp = &fpu->state.fsave;
                fp->cwd = 0xffff037fu;
                fp->swd = 0xffff0000u;
                fp->twd = 0xffffffffu;
                fp->fos = 0xffff0000u;
        }
}
EXPORT_SYMBOL_GPL(fpstate_init);

/*
 * 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.
 */
static void fpu_copy(struct fpu *dst_fpu, struct fpu *src_fpu)
{
        WARN_ON(src_fpu != &current->thread.fpu);

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

        /*
         * Save current FPU registers directly into the child
         * FPU context, without any memory-to-memory copying.
         *
         * If the FPU context got destroyed in the process (FNSAVE
         * done on old CPUs) then copy it back into the source
         * context and mark the current task for lazy restore.
         *
         * We have to do all this with preemption disabled,
         * mostly because of the FNSAVE case, because in that
         * case we must not allow preemption in the window
         * between the FNSAVE and us marking the context lazy.
         *
         * It shouldn't be an issue as even FNSAVE is plenty
         * fast in terms of critical section length.
         */
        preempt_disable();
        if (!copy_fpregs_to_fpstate(dst_fpu)) {
                memcpy(&src_fpu->state, &dst_fpu->state, xstate_size);
                fpregs_deactivate(src_fpu);
        }
        preempt_enable();
}

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

        if (src_fpu->fpstate_active)
                fpu_copy(dst_fpu, src_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_ONCE(fpu != &current->thread.fpu);

        if (!fpu->fpstate_active) {
                fpstate_init(fpu);

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

/*
 * This function must be called before we modify a stopped child's
 * fpstate.
 *
 * If the child has not used the FPU before then initialize its
 * fpstate.
 *
 * If the child has used the FPU before then unlazy it.
 *
 * [ 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 lazy status here then the lazy in-registers
 *   state pending on its former CPU could be restored, corrupting
 *   the modifications. ]
 *
 * This function is also called before we read a stopped child's
 * FPU state - to make sure it's initialized if the child has
 * no active FPU state.
 *
 * 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.
 */
static void fpu__activate_stopped(struct fpu *child_fpu)
{
        WARN_ON_ONCE(child_fpu == &current->thread.fpu);

        if (child_fpu->fpstate_active) {
                child_fpu->last_cpu = -1;
        } else {
                fpstate_init(child_fpu);

                /* Safe to do for stopped child tasks: */
                child_fpu->fpstate_active = 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(void)
{
        struct task_struct *tsk = current;
        struct fpu *fpu = &tsk->thread.fpu;

        fpu__activate_curr(fpu);

        /* Avoid __kernel_fpu_begin() right after fpregs_activate() */
        kernel_fpu_disable();
        fpregs_activate(fpu);
        if (unlikely(copy_fpstate_to_fpregs(fpu))) {
                fpu__clear(fpu);
                force_sig_info(SIGSEGV, SEND_SIG_PRIV, tsk);
        } else {
                tsk->thread.fpu.counter++;
        }
        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();
        fpu->counter = 0;

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

        fpu->fpstate_active = 0;

        preempt_enable();
}

/*
 * 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_ONCE(fpu != &current->thread.fpu); /* Almost certainly an anomaly */

        if (!use_eager_fpu()) {
                /* FPU state will be reallocated lazily at the first use. */
                fpu__drop(fpu);
        } else {
                if (!fpu->fpstate_active) {
                        fpu__activate_curr(fpu);
                        user_fpu_begin();
                }
                restore_init_xstate();
        }
}

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

        return target_fpu->fpstate_active ? regset->n : 0;
}

int regset_xregset_fpregs_active(struct task_struct *target, const struct user_regset *regset)
{
        struct fpu *target_fpu = &target->thread.fpu;

        return (cpu_has_fxsr && target_fpu->fpstate_active) ? regset->n : 0;
}

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

        if (!cpu_has_fxsr)
                return -ENODEV;

        fpu__activate_stopped(fpu);
        fpstate_sanitize_xstate(fpu);

        return user_regset_copyout(&pos, &count, &kbuf, &ubuf,
                                   &fpu->state.fxsave, 0, -1);
}

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)
{
        struct fpu *fpu = &target->thread.fpu;
        int ret;

        if (!cpu_has_fxsr)
                return -ENODEV;

        fpu__activate_stopped(fpu);
        fpstate_sanitize_xstate(fpu);

        ret = user_regset_copyin(&pos, &count, &kbuf, &ubuf,
                                 &fpu->state.fxsave, 0, -1);

        /*
         * mxcsr reserved bits must be masked to zero for security reasons.
         */
        fpu->state.fxsave.mxcsr &= mxcsr_feature_mask;

        /*
         * update the header bits in the xsave header, indicating the
         * presence of FP and SSE state.
         */
        if (cpu_has_xsave)
                fpu->state.xsave.header.xfeatures |= XSTATE_FPSSE;

        return ret;
}

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

        if (!cpu_has_xsave)
                return -ENODEV;

        fpu__activate_stopped(fpu);

        xsave = &fpu->state.xsave;

        /*
         * 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().
         */
        memcpy(&xsave->i387.sw_reserved,
                xstate_fx_sw_bytes, sizeof(xstate_fx_sw_bytes));
        /*
         * Copy the xstate memory layout.
         */
        ret = user_regset_copyout(&pos, &count, &kbuf, &ubuf, xsave, 0, -1);
        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)
{
        struct fpu *fpu = &target->thread.fpu;
        struct xsave_struct *xsave;
        int ret;

        if (!cpu_has_xsave)
                return -ENODEV;

        fpu__activate_stopped(fpu);

        xsave = &fpu->state.xsave;

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

        return ret;
}

#if defined CONFIG_X86_32 || defined CONFIG_IA32_EMULATION

/*
 * FPU tag word conversions.
 */

static inline unsigned short twd_i387_to_fxsr(unsigned short twd)
{
        unsigned int tmp; /* to avoid 16 bit prefixes in the code */

        /* Transform each pair of bits into 01 (valid) or 00 (empty) */
        tmp = ~twd;
        tmp = (tmp | (tmp>>1)) & 0x5555; /* 0V0V0V0V0V0V0V0V */
        /* 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 */

        return tmp;
}

#define FPREG_ADDR(f, n)        ((void *)&(f)->st_space + (n) * 16)
#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;

        for (i = 0; i < 8; i++, twd >>= 1) {
                if (twd & 0x1) {
                        st = FPREG_ADDR(fxsave, (i - tos) & 7);

                        switch (st->exponent & 0x7fff) {
                        case 0x7fff:
                                tag = FP_EXP_TAG_SPECIAL;
                                break;
                        case 0x0000:
                                if (!st->significand[0] &&
                                    !st->significand[1] &&
                                    !st->significand[2] &&
                                    !st->significand[3])
                                        tag = FP_EXP_TAG_ZERO;
                                else
                                        tag = FP_EXP_TAG_SPECIAL;
                                break;
                        default:
                                if (st->significand[3] & 0x8000)
                                        tag = FP_EXP_TAG_VALID;
                                else
                                        tag = FP_EXP_TAG_SPECIAL;
                                break;
                        }
                } else {
                        tag = FP_EXP_TAG_EMPTY;
                }
                ret |= tag << (2 * i);
        }
        return ret;
}

/*
 * FXSR floating point environment conversions.
 */

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

        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;
        /*
         * 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;
        if (tsk == current) {
                savesegment(ds, env->fos);
        } else {
                env->fos = tsk->thread.ds;
        }
        env->fos |= 0xffff0000;
#else
        env->fip = fxsave->fip;
        env->fcs = (u16) fxsave->fcs | ((u32) fxsave->fop << 16);
        env->foo = fxsave->foo;
        env->fos = fxsave->fos;
#endif

        for (i = 0; i < 8; ++i)
                memcpy(&to[i], &from[i], sizeof(to[0]));
}

void convert_to_fxsr(struct task_struct *tsk,
                     const struct user_i387_ia32_struct *env)

{
        struct i387_fxsave_struct *fxsave = &tsk->thread.fpu.state.fxsave;
        struct _fpreg *from = (struct _fpreg *) &env->st_space[0];
        struct _fpxreg *to = (struct _fpxreg *) &fxsave->st_space[0];
        int i;

        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

        for (i = 0; i < 8; ++i)
                memcpy(&to[i], &from[i], sizeof(from[0]));
}

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

        fpu__activate_stopped(fpu);

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

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

        fpstate_sanitize_xstate(fpu);

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

        convert_from_fxsr(&env, target);

        return user_regset_copyout(&pos, &count, &kbuf, &ubuf, &env, 0, -1);
}

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)
{
        struct fpu *fpu = &target->thread.fpu;
        struct user_i387_ia32_struct env;
        int ret;

        fpu__activate_stopped(fpu);
        fpstate_sanitize_xstate(fpu);

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

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

        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);

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

/*
 * FPU state for core dumps.
 * 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.
 */
int dump_fpu(struct pt_regs *regs, struct user_i387_struct *ufpu)
{
        struct task_struct *tsk = current;
        struct fpu *fpu = &tsk->thread.fpu;
        int fpvalid;

        fpvalid = fpu->fpstate_active;
        if (fpvalid)
                fpvalid = !fpregs_get(tsk, NULL,
                                      0, sizeof(struct user_i387_ia32_struct),
                                      ufpu, NULL);

        return fpvalid;
}
EXPORT_SYMBOL(dump_fpu);

#endif  /* CONFIG_X86_32 || CONFIG_IA32_EMULATION */