x86/fpu: Rename all the fpregs, xregs, fxregs and fregs handling functions

[mirror_ubuntu-artful-kernel.git] / arch / x86 / kernel / fpu / xstate.c

/*
 * xsave/xrstor support.
 *
 * Author: Suresh Siddha <suresh.b.siddha@intel.com>
 */
#include <linux/compat.h>
#include <linux/cpu.h>

#include <asm/fpu/api.h>
#include <asm/fpu/internal.h>
#include <asm/fpu/signal.h>
#include <asm/fpu/regset.h>
#include <asm/sigframe.h>
#include <asm/tlbflush.h>

static const char *xfeature_names[] =
{
        "x87 floating point registers"  ,
        "SSE registers"                 ,
        "AVX registers"                 ,
        "MPX bounds registers"          ,
        "MPX CSR"                       ,
        "AVX-512 opmask"                ,
        "AVX-512 Hi256"                 ,
        "AVX-512 ZMM_Hi256"             ,
        "unknown xstate feature"        ,
};

/*
 * Mask of xstate features supported by the CPU and the kernel:
 */
u64 xfeatures_mask __read_mostly;

static struct _fpx_sw_bytes fx_sw_reserved, fx_sw_reserved_ia32;
static unsigned int xstate_offsets[XFEATURES_NR_MAX], xstate_sizes[XFEATURES_NR_MAX];
static unsigned int xstate_comp_offsets[sizeof(xfeatures_mask)*8];

/* The number of supported xfeatures in xfeatures_mask: */
static unsigned int xfeatures_nr;

/*
 * Return whether the system supports a given xfeature.
 *
 * Also return the name of the (most advanced) feature that the caller requested:
 */
int cpu_has_xfeatures(u64 xfeatures_needed, const char **feature_name)
{
        u64 xfeatures_missing = xfeatures_needed & ~xfeatures_mask;

        if (unlikely(feature_name)) {
                long xfeature_idx, max_idx;
                u64 xfeatures_print;
                /*
                 * So we use FLS here to be able to print the most advanced
                 * feature that was requested but is missing. So if a driver
                 * asks about "XSTATE_SSE | XSTATE_YMM" we'll print the
                 * missing AVX feature - this is the most informative message
                 * to users:
                 */
                if (xfeatures_missing)
                        xfeatures_print = xfeatures_missing;
                else
                        xfeatures_print = xfeatures_needed;

                xfeature_idx = fls64(xfeatures_print)-1;
                max_idx = ARRAY_SIZE(xfeature_names)-1;
                xfeature_idx = min(xfeature_idx, max_idx);

                *feature_name = xfeature_names[xfeature_idx];
        }

        if (xfeatures_missing)
                return 0;

        return 1;
}
EXPORT_SYMBOL_GPL(cpu_has_xfeatures);

/*
 * When executing XSAVEOPT (optimized XSAVE), if a processor implementation
 * detects that an FPU state component is still (or is again) in its
 * initialized state, it may clear the corresponding bit in the header.xfeatures
 * field, and can skip the writeout of registers to the corresponding memory layout.
 *
 * This means that when the bit is zero, the state component might still contain
 * some previous - non-initialized register state.
 *
 * Before writing xstate information to user-space we sanitize those components,
 * to always ensure that the memory layout of a feature will be in the init state
 * if the corresponding header bit is zero. This is to ensure that user-space doesn't
 * see some stale state in the memory layout during signal handling, debugging etc.
 */
void fpstate_sanitize_xstate(struct fpu *fpu)
{
        struct i387_fxsave_struct *fx = &fpu->state.fxsave;
        int feature_bit;
        u64 xfeatures;

        if (!use_xsaveopt())
                return;

        xfeatures = fpu->state.xsave.header.xfeatures;

        /*
         * None of the feature bits are in init state. So nothing else
         * to do for us, as the memory layout is up to date.
         */
        if ((xfeatures & xfeatures_mask) == xfeatures_mask)
                return;

        /*
         * FP is in init state
         */
        if (!(xfeatures & XSTATE_FP)) {
                fx->cwd = 0x37f;
                fx->swd = 0;
                fx->twd = 0;
                fx->fop = 0;
                fx->rip = 0;
                fx->rdp = 0;
                memset(&fx->st_space[0], 0, 128);
        }

        /*
         * SSE is in init state
         */
        if (!(xfeatures & XSTATE_SSE))
                memset(&fx->xmm_space[0], 0, 256);

        /*
         * First two features are FPU and SSE, which above we handled
         * in a special way already:
         */
        feature_bit = 0x2;
        xfeatures = (xfeatures_mask & ~xfeatures) >> 2;

        /*
         * Update all the remaining memory layouts according to their
         * standard xstate layout, if their header bit is in the init
         * state:
         */
        while (xfeatures) {
                if (xfeatures & 0x1) {
                        int offset = xstate_offsets[feature_bit];
                        int size = xstate_sizes[feature_bit];

                        memcpy((void *)fx + offset,
                               (void *)&init_fpstate.xsave + offset,
                               size);
                }

                xfeatures >>= 1;
                feature_bit++;
        }
}

/*
 * Check for the presence of extended state information in the
 * user fpstate pointer in the sigcontext.
 */
static inline int check_for_xstate(struct i387_fxsave_struct __user *buf,
                                   void __user *fpstate,
                                   struct _fpx_sw_bytes *fx_sw)
{
        int min_xstate_size = sizeof(struct i387_fxsave_struct) +
                              sizeof(struct xstate_header);
        unsigned int magic2;

        if (__copy_from_user(fx_sw, &buf->sw_reserved[0], sizeof(*fx_sw)))
                return -1;

        /* Check for the first magic field and other error scenarios. */
        if (fx_sw->magic1 != FP_XSTATE_MAGIC1 ||
            fx_sw->xstate_size < min_xstate_size ||
            fx_sw->xstate_size > xstate_size ||
            fx_sw->xstate_size > fx_sw->extended_size)
                return -1;

        /*
         * Check for the presence of second magic word at the end of memory
         * layout. This detects the case where the user just copied the legacy
         * fpstate layout with out copying the extended state information
         * in the memory layout.
         */
        if (__get_user(magic2, (__u32 __user *)(fpstate + fx_sw->xstate_size))
            || magic2 != FP_XSTATE_MAGIC2)
                return -1;

        return 0;
}

/*
 * Signal frame handlers.
 */
static inline int save_fsave_header(struct task_struct *tsk, void __user *buf)
{
        if (use_fxsr()) {
                struct xsave_struct *xsave = &tsk->thread.fpu.state.xsave;
                struct user_i387_ia32_struct env;
                struct _fpstate_ia32 __user *fp = buf;

                convert_from_fxsr(&env, tsk);

                if (__copy_to_user(buf, &env, sizeof(env)) ||
                    __put_user(xsave->i387.swd, &fp->status) ||
                    __put_user(X86_FXSR_MAGIC, &fp->magic))
                        return -1;
        } else {
                struct i387_fsave_struct __user *fp = buf;
                u32 swd;
                if (__get_user(swd, &fp->swd) || __put_user(swd, &fp->status))
                        return -1;
        }

        return 0;
}

static inline int save_xstate_epilog(void __user *buf, int ia32_frame)
{
        struct xsave_struct __user *x = buf;
        struct _fpx_sw_bytes *sw_bytes;
        u32 xfeatures;
        int err;

        /* Setup the bytes not touched by the [f]xsave and reserved for SW. */
        sw_bytes = ia32_frame ? &fx_sw_reserved_ia32 : &fx_sw_reserved;
        err = __copy_to_user(&x->i387.sw_reserved, sw_bytes, sizeof(*sw_bytes));

        if (!use_xsave())
                return err;

        err |= __put_user(FP_XSTATE_MAGIC2, (__u32 *)(buf + xstate_size));

        /*
         * Read the xfeatures which we copied (directly from the cpu or
         * from the state in task struct) to the user buffers.
         */
        err |= __get_user(xfeatures, (__u32 *)&x->header.xfeatures);

        /*
         * For legacy compatible, we always set FP/SSE bits in the bit
         * vector while saving the state to the user context. This will
         * enable us capturing any changes(during sigreturn) to
         * the FP/SSE bits by the legacy applications which don't touch
         * xfeatures in the xsave header.
         *
         * xsave aware apps can change the xfeatures in the xsave
         * header as well as change any contents in the memory layout.
         * xrestore as part of sigreturn will capture all the changes.
         */
        xfeatures |= XSTATE_FPSSE;

        err |= __put_user(xfeatures, (__u32 *)&x->header.xfeatures);

        return err;
}

static inline int copy_fpregs_to_sigframe(struct xsave_struct __user *buf)
{
        int err;

        if (use_xsave())
                err = copy_xregs_to_user(buf);
        else if (use_fxsr())
                err = copy_fxregs_to_user((struct i387_fxsave_struct __user *) buf);
        else
                err = copy_fregs_to_user((struct i387_fsave_struct __user *) buf);

        if (unlikely(err) && __clear_user(buf, xstate_size))
                err = -EFAULT;
        return err;
}

/*
 * Save the fpu, extended register state to the user signal frame.
 *
 * 'buf_fx' is the 64-byte aligned pointer at which the [f|fx|x]save
 *  state is copied.
 *  'buf' points to the 'buf_fx' or to the fsave header followed by 'buf_fx'.
 *
 *      buf == buf_fx for 64-bit frames and 32-bit fsave frame.
 *      buf != buf_fx for 32-bit frames with fxstate.
 *
 * If the fpu, extended register state is live, save the state directly
 * to the user frame pointed by the aligned pointer 'buf_fx'. Otherwise,
 * copy the thread's fpu state to the user frame starting at 'buf_fx'.
 *
 * If this is a 32-bit frame with fxstate, put a fsave header before
 * the aligned state at 'buf_fx'.
 *
 * For [f]xsave state, update the SW reserved fields in the [f]xsave frame
 * indicating the absence/presence of the extended state to the user.
 */
int copy_fpstate_to_sigframe(void __user *buf, void __user *buf_fx, int size)
{
        struct xsave_struct *xsave = &current->thread.fpu.state.xsave;
        struct task_struct *tsk = current;
        int ia32_fxstate = (buf != buf_fx);

        ia32_fxstate &= (config_enabled(CONFIG_X86_32) ||
                         config_enabled(CONFIG_IA32_EMULATION));

        if (!access_ok(VERIFY_WRITE, buf, size))
                return -EACCES;

        if (!static_cpu_has(X86_FEATURE_FPU))
                return fpregs_soft_get(current, NULL, 0,
                        sizeof(struct user_i387_ia32_struct), NULL,
                        (struct _fpstate_ia32 __user *) buf) ? -1 : 1;

        if (fpregs_active()) {
                /* Save the live register state to the user directly. */
                if (copy_fpregs_to_sigframe(buf_fx))
                        return -1;
                /* Update the thread's fxstate to save the fsave header. */
                if (ia32_fxstate)
                        copy_fxregs_to_kernel(&tsk->thread.fpu);
        } else {
                fpstate_sanitize_xstate(&tsk->thread.fpu);
                if (__copy_to_user(buf_fx, xsave, xstate_size))
                        return -1;
        }

        /* Save the fsave header for the 32-bit frames. */
        if ((ia32_fxstate || !use_fxsr()) && save_fsave_header(tsk, buf))
                return -1;

        if (use_fxsr() && save_xstate_epilog(buf_fx, ia32_fxstate))
                return -1;

        return 0;
}

static inline void
sanitize_restored_xstate(struct task_struct *tsk,
                         struct user_i387_ia32_struct *ia32_env,
                         u64 xfeatures, int fx_only)
{
        struct xsave_struct *xsave = &tsk->thread.fpu.state.xsave;
        struct xstate_header *header = &xsave->header;

        if (use_xsave()) {
                /* These bits must be zero. */
                memset(header->reserved, 0, 48);

                /*
                 * Init the state that is not present in the memory
                 * layout and not enabled by the OS.
                 */
                if (fx_only)
                        header->xfeatures = XSTATE_FPSSE;
                else
                        header->xfeatures &= (xfeatures_mask & xfeatures);
        }

        if (use_fxsr()) {
                /*
                 * mscsr reserved bits must be masked to zero for security
                 * reasons.
                 */
                xsave->i387.mxcsr &= mxcsr_feature_mask;

                convert_to_fxsr(tsk, ia32_env);
        }
}

/*
 * Restore the extended state if present. Otherwise, restore the FP/SSE state.
 */
static inline int copy_user_to_fpregs_zeroing(void __user *buf, u64 xbv, int fx_only)
{
        if (use_xsave()) {
                if ((unsigned long)buf % 64 || fx_only) {
                        u64 init_bv = xfeatures_mask & ~XSTATE_FPSSE;
                        copy_kernel_to_xregs(&init_fpstate.xsave, init_bv);
                        return copy_user_to_fxregs(buf);
                } else {
                        u64 init_bv = xfeatures_mask & ~xbv;
                        if (unlikely(init_bv))
                                copy_kernel_to_xregs(&init_fpstate.xsave, init_bv);
                        return copy_user_to_xregs(buf, xbv);
                }
        } else if (use_fxsr()) {
                return copy_user_to_fxregs(buf);
        } else
                return copy_user_to_fregs(buf);
}

static int __fpu__restore_sig(void __user *buf, void __user *buf_fx, int size)
{
        int ia32_fxstate = (buf != buf_fx);
        struct task_struct *tsk = current;
        struct fpu *fpu = &tsk->thread.fpu;
        int state_size = xstate_size;
        u64 xfeatures = 0;
        int fx_only = 0;

        ia32_fxstate &= (config_enabled(CONFIG_X86_32) ||
                         config_enabled(CONFIG_IA32_EMULATION));

        if (!buf) {
                fpu__clear(fpu);
                return 0;
        }

        if (!access_ok(VERIFY_READ, buf, size))
                return -EACCES;

        fpu__activate_curr(fpu);

        if (!static_cpu_has(X86_FEATURE_FPU))
                return fpregs_soft_set(current, NULL,
                                       0, sizeof(struct user_i387_ia32_struct),
                                       NULL, buf) != 0;

        if (use_xsave()) {
                struct _fpx_sw_bytes fx_sw_user;
                if (unlikely(check_for_xstate(buf_fx, buf_fx, &fx_sw_user))) {
                        /*
                         * Couldn't find the extended state information in the
                         * memory layout. Restore just the FP/SSE and init all
                         * the other extended state.
                         */
                        state_size = sizeof(struct i387_fxsave_struct);
                        fx_only = 1;
                } else {
                        state_size = fx_sw_user.xstate_size;
                        xfeatures = fx_sw_user.xfeatures;
                }
        }

        if (ia32_fxstate) {
                /*
                 * For 32-bit frames with fxstate, copy the user state to the
                 * thread's fpu state, reconstruct fxstate from the fsave
                 * header. Sanitize the copied state etc.
                 */
                struct fpu *fpu = &tsk->thread.fpu;
                struct user_i387_ia32_struct env;
                int err = 0;

                /*
                 * Drop the current fpu which clears fpu->fpstate_active. 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
                 * fpu->fpstate_active is again set.
                 */
                fpu__drop(fpu);

                if (__copy_from_user(&fpu->state.xsave, buf_fx, state_size) ||
                    __copy_from_user(&env, buf, sizeof(env))) {
                        fpstate_init(&fpu->state);
                        err = -1;
                } else {
                        sanitize_restored_xstate(tsk, &env, xfeatures, fx_only);
                }

                fpu->fpstate_active = 1;
                if (use_eager_fpu()) {
                        preempt_disable();
                        fpu__restore();
                        preempt_enable();
                }

                return err;
        } else {
                /*
                 * For 64-bit frames and 32-bit fsave frames, restore the user
                 * state to the registers directly (with exceptions handled).
                 */
                user_fpu_begin();
                if (copy_user_to_fpregs_zeroing(buf_fx, xfeatures, fx_only)) {
                        fpu__clear(fpu);
                        return -1;
                }
        }

        return 0;
}

static inline int xstate_sigframe_size(void)
{
        return use_xsave() ? xstate_size + FP_XSTATE_MAGIC2_SIZE : xstate_size;
}

/*
 * Restore FPU state from a sigframe:
 */
int fpu__restore_sig(void __user *buf, int ia32_frame)
{
        void __user *buf_fx = buf;
        int size = xstate_sigframe_size();

        if (ia32_frame && use_fxsr()) {
                buf_fx = buf + sizeof(struct i387_fsave_struct);
                size += sizeof(struct i387_fsave_struct);
        }

        return __fpu__restore_sig(buf, buf_fx, size);
}

unsigned long
fpu__alloc_mathframe(unsigned long sp, int ia32_frame,
                     unsigned long *buf_fx, unsigned long *size)
{
        unsigned long frame_size = xstate_sigframe_size();

        *buf_fx = sp = round_down(sp - frame_size, 64);
        if (ia32_frame && use_fxsr()) {
                frame_size += sizeof(struct i387_fsave_struct);
                sp -= sizeof(struct i387_fsave_struct);
        }

        *size = frame_size;

        return sp;
}
/*
 * Prepare the SW reserved portion of the fxsave memory layout, indicating
 * the presence of the extended state information in the memory layout
 * pointed by the fpstate pointer in the sigcontext.
 * This will be saved when ever the FP and extended state context is
 * saved on the user stack during the signal handler delivery to the user.
 */
static void prepare_fx_sw_frame(void)
{
        int fsave_header_size = sizeof(struct i387_fsave_struct);
        int size = xstate_size + FP_XSTATE_MAGIC2_SIZE;

        if (config_enabled(CONFIG_X86_32))
                size += fsave_header_size;

        fx_sw_reserved.magic1 = FP_XSTATE_MAGIC1;
        fx_sw_reserved.extended_size = size;
        fx_sw_reserved.xfeatures = xfeatures_mask;
        fx_sw_reserved.xstate_size = xstate_size;

        if (config_enabled(CONFIG_IA32_EMULATION)) {
                fx_sw_reserved_ia32 = fx_sw_reserved;
                fx_sw_reserved_ia32.extended_size += fsave_header_size;
        }
}

/*
 * Enable the extended processor state save/restore feature.
 * Called once per CPU onlining.
 */
void fpu__init_cpu_xstate(void)
{
        if (!cpu_has_xsave || !xfeatures_mask)
                return;

        cr4_set_bits(X86_CR4_OSXSAVE);
        xsetbv(XCR_XFEATURE_ENABLED_MASK, xfeatures_mask);
}

/*
 * Record the offsets and sizes of different state managed by the xsave
 * memory layout.
 */
static void __init setup_xstate_features(void)
{
        int eax, ebx, ecx, edx, leaf = 0x2;

        xfeatures_nr = fls64(xfeatures_mask);

        do {
                cpuid_count(XSTATE_CPUID, leaf, &eax, &ebx, &ecx, &edx);

                if (eax == 0)
                        break;

                xstate_offsets[leaf] = ebx;
                xstate_sizes[leaf] = eax;

                leaf++;
        } while (1);
}

static void print_xstate_feature(u64 xstate_mask)
{
        const char *feature_name;

        if (cpu_has_xfeatures(xstate_mask, &feature_name))
                pr_info("x86/fpu: Supporting XSAVE feature 0x%02Lx: '%s'\n", xstate_mask, feature_name);
}

/*
 * Print out all the supported xstate features:
 */
static void print_xstate_features(void)
{
        print_xstate_feature(XSTATE_FP);
        print_xstate_feature(XSTATE_SSE);
        print_xstate_feature(XSTATE_YMM);
        print_xstate_feature(XSTATE_BNDREGS);
        print_xstate_feature(XSTATE_BNDCSR);
        print_xstate_feature(XSTATE_OPMASK);
        print_xstate_feature(XSTATE_ZMM_Hi256);
        print_xstate_feature(XSTATE_Hi16_ZMM);
}

/*
 * This function sets up offsets and sizes of all extended states in
 * xsave area. This supports both standard format and compacted format
 * of the xsave aread.
 *
 * Input: void
 * Output: void
 */
void setup_xstate_comp(void)
{
        unsigned int xstate_comp_sizes[sizeof(xfeatures_mask)*8];
        int i;

        /*
         * The FP xstates and SSE xstates are legacy states. They are always
         * in the fixed offsets in the xsave area in either compacted form
         * or standard form.
         */
        xstate_comp_offsets[0] = 0;
        xstate_comp_offsets[1] = offsetof(struct i387_fxsave_struct, xmm_space);

        if (!cpu_has_xsaves) {
                for (i = 2; i < xfeatures_nr; i++) {
                        if (test_bit(i, (unsigned long *)&xfeatures_mask)) {
                                xstate_comp_offsets[i] = xstate_offsets[i];
                                xstate_comp_sizes[i] = xstate_sizes[i];
                        }
                }
                return;
        }

        xstate_comp_offsets[2] = FXSAVE_SIZE + XSAVE_HDR_SIZE;

        for (i = 2; i < xfeatures_nr; i++) {
                if (test_bit(i, (unsigned long *)&xfeatures_mask))
                        xstate_comp_sizes[i] = xstate_sizes[i];
                else
                        xstate_comp_sizes[i] = 0;

                if (i > 2)
                        xstate_comp_offsets[i] = xstate_comp_offsets[i-1]
                                        + xstate_comp_sizes[i-1];

        }
}

/*
 * setup the xstate image representing the init state
 */
static void setup_init_fpu_buf(void)
{
        if (!cpu_has_xsave)
                return;

        setup_xstate_features();
        print_xstate_features();

        if (cpu_has_xsaves) {
                init_fpstate.xsave.header.xcomp_bv = (u64)1 << 63 | xfeatures_mask;
                init_fpstate.xsave.header.xfeatures = xfeatures_mask;
        }

        /*
         * Init all the features state with header_bv being 0x0
         */
        copy_kernel_to_xregs_booting(&init_fpstate.xsave, -1);

        /*
         * Dump the init state again. This is to identify the init state
         * of any feature which is not represented by all zero's.
         */
        copy_xregs_to_kernel_booting(&init_fpstate.xsave);
}

/*
 * Calculate total size of enabled xstates in XCR0/xfeatures_mask.
 */
static void __init init_xstate_size(void)
{
        unsigned int eax, ebx, ecx, edx;
        int i;

        if (!cpu_has_xsaves) {
                cpuid_count(XSTATE_CPUID, 0, &eax, &ebx, &ecx, &edx);
                xstate_size = ebx;
                return;
        }

        xstate_size = FXSAVE_SIZE + XSAVE_HDR_SIZE;
        for (i = 2; i < 64; i++) {
                if (test_bit(i, (unsigned long *)&xfeatures_mask)) {
                        cpuid_count(XSTATE_CPUID, i, &eax, &ebx, &ecx, &edx);
                        xstate_size += eax;
                }
        }
}

/*
 * Enable and initialize the xsave feature.
 * Called once per system bootup.
 *
 * ( Not marked __init because of false positive section warnings. )
 */
void fpu__init_system_xstate(void)
{
        unsigned int eax, ebx, ecx, edx;

        if (!cpu_has_xsave) {
                pr_info("x86/fpu: Legacy x87 FPU detected.\n");
                return;
        }

        if (boot_cpu_data.cpuid_level < XSTATE_CPUID) {
                WARN(1, "x86/fpu: XSTATE_CPUID missing!\n");
                return;
        }

        cpuid_count(XSTATE_CPUID, 0, &eax, &ebx, &ecx, &edx);
        xfeatures_mask = eax + ((u64)edx << 32);

        if ((xfeatures_mask & XSTATE_FPSSE) != XSTATE_FPSSE) {
                pr_err("x86/fpu: FP/SSE not present amongst the CPU's xstate features: 0x%llx.\n", xfeatures_mask);
                BUG();
        }

        /*
         * Support only the state known to OS.
         */
        xfeatures_mask = xfeatures_mask & XCNTXT_MASK;

        /* Enable xstate instructions to be able to continue with initialization: */
        fpu__init_cpu_xstate();

        /*
         * Recompute the context size for enabled features
         */
        init_xstate_size();

        update_regset_xstate_info(xstate_size, xfeatures_mask);
        prepare_fx_sw_frame();
        setup_init_fpu_buf();

        pr_info("x86/fpu: Enabled xstate features 0x%llx, context size is 0x%x bytes, using '%s' format.\n",
                xfeatures_mask,
                xstate_size,
                cpu_has_xsaves ? "compacted" : "standard");
}

/*
 * Restore minimal FPU state after suspend:
 */
void fpu__resume_cpu(void)
{
        /*
         * Restore XCR0 on xsave capable CPUs:
         */
        if (cpu_has_xsave)
                xsetbv(XCR_XFEATURE_ENABLED_MASK, xfeatures_mask);
}

/*
 * Given the xsave area and a state inside, this function returns the
 * address of the state.
 *
 * This is the API that is called to get xstate address in either
 * standard format or compacted format of xsave area.
 *
 * Inputs:
 *      xsave: base address of the xsave area;
 *      xstate: state which is defined in xsave.h (e.g. XSTATE_FP, XSTATE_SSE,
 *      etc.)
 * Output:
 *      address of the state in the xsave area.
 */
void *get_xsave_addr(struct xsave_struct *xsave, int xstate)
{
        int feature = fls64(xstate) - 1;
        if (!test_bit(feature, (unsigned long *)&xfeatures_mask))
                return NULL;

        return (void *)xsave + xstate_comp_offsets[feature];
}
EXPORT_SYMBOL_GPL(get_xsave_addr);