text: /*
   * xsave/xrstor support.
   *
   * Author: Suresh Siddha <suresh.b.siddha@intel.com>
   */
  
  #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  
  #include <linux/bootmem.h>
  #include <linux/compat.h>
  #include <linux/cpu.h>
  #include <asm/i387.h>
  #include <asm/fpu-internal.h>
  #include <asm/sigframe.h>
  #include <asm/tlbflush.h>
  #include <asm/xcr.h>
  
  /*
   * Supported feature mask by the CPU and the kernel.
   */
  u64 pcntxt_mask;
  
  /*
   * Represents init state for the supported extended state.
   */
  struct xsave_struct *init_xstate_buf;
  
  static struct _fpx_sw_bytes fx_sw_reserved, fx_sw_reserved_ia32;
  static unsigned int *xstate_offsets, *xstate_sizes;
  static unsigned int xstate_comp_offsets[sizeof(pcntxt_mask)*8];
  static unsigned int xstate_features;
  
  /*
   * If a processor implementation discern that a processor state component is
   * in its initialized state it may modify the corresponding bit in the
   * xsave_hdr.xstate_bv as '0', with out modifying the corresponding memory
   * layout in the case of xsaveopt. While presenting the xstate information to
   * the user, we 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 the user doesn't see some stale state in the memory layout during
   * signal handling, debugging etc.
   */
  void __sanitize_i387_state(struct task_struct *tsk)
  {
  	struct i387_fxsave_struct *fx = &tsk->thread.fpu.state->fxsave;
  	int feature_bit = 0x2;
  	u64 xstate_bv;
  
  	if (!fx)
  		return;
  
  	xstate_bv = tsk->thread.fpu.state->xsave.xsave_hdr.xstate_bv;
  
  	/*
  	 * 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 ((xstate_bv & pcntxt_mask) == pcntxt_mask)
  		return;
  
  	/*
  	 * FP is in init state
  	 */
  	if (!(xstate_bv & 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 (!(xstate_bv & XSTATE_SSE))
  		memset(&fx->xmm_space[0], 0, 256);
  
  	xstate_bv = (pcntxt_mask & ~xstate_bv) >> 2;
  
  	/*
  	 * Update all the other memory layouts for which the corresponding
  	 * header bit is in the init state.
  	 */
  	while (xstate_bv) {
  		if (xstate_bv & 0x1) {
  			int offset = xstate_offsets[feature_bit];
  			int size = xstate_sizes[feature_bit];
  
  			memcpy(((void *) fx) + offset,
  			       ((void *) init_xstate_buf) + offset,
  			       size);
  		}
  
  		xstate_bv >>= 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 xsave_hdr_struct);
  	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 xstate_bv;
  	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 xstate_bv which we copied (directly from the cpu or
  	 * from the state in task struct) to the user buffers.
  	 */
  	err |= __get_user(xstate_bv, (__u32 *)&x->xsave_hdr.xstate_bv);
  
  	/*
  	 * 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
  	 * xstate_bv in the xsave header.
  	 *
  	 * xsave aware apps can change the xstate_bv in the xsave
  	 * header as well as change any contents in the memory layout.
  	 * xrestore as part of sigreturn will capture all the changes.
  	 */
  	xstate_bv |= XSTATE_FPSSE;
  
  	err |= __put_user(xstate_bv, (__u32 *)&x->xsave_hdr.xstate_bv);
  
  	return err;
  }
  
  static inline int save_user_xstate(struct xsave_struct __user *buf)
  {
  	int err;
  
  	if (use_xsave())
  		err = xsave_user(buf);
  	else if (use_fxsr())
  		err = fxsave_user((struct i387_fxsave_struct __user *) buf);
  	else
  		err = fsave_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 save_xstate_sig(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 (user_has_fpu()) {
  		/* Save the live register state to the user directly. */
  		if (save_user_xstate(buf_fx))
  			return -1;
  		/* Update the thread's fxstate to save the fsave header. */
  		if (ia32_fxstate)
  			fpu_fxsave(&tsk->thread.fpu);
  	} else {
  		sanitize_i387_state(tsk);
  		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 xstate_bv, int fx_only)
  {
  	struct xsave_struct *xsave = &tsk->thread.fpu.state->xsave;
  	struct xsave_hdr_struct *xsave_hdr = &xsave->xsave_hdr;
  
  	if (use_xsave()) {
  		/* These bits must be zero. */
  		memset(xsave_hdr->reserved, 0, 48);
  
  		/*
  		 * Init the state that is not present in the memory
  		 * layout and not enabled by the OS.
  		 */
  		if (fx_only)
  			xsave_hdr->xstate_bv = XSTATE_FPSSE;
  		else
  			xsave_hdr->xstate_bv &= (pcntxt_mask & xstate_bv);
  	}
  
  	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 restore_user_xstate(void __user *buf, u64 xbv, int fx_only)
  {
  	if (use_xsave()) {
  		if ((unsigned long)buf % 64 || fx_only) {
  			u64 init_bv = pcntxt_mask & ~XSTATE_FPSSE;
  			xrstor_state(init_xstate_buf, init_bv);
  			return fxrstor_user(buf);
  		} else {
  			u64 init_bv = pcntxt_mask & ~xbv;
  			if (unlikely(init_bv))
  				xrstor_state(init_xstate_buf, init_bv);
  			return xrestore_user(buf, xbv);
  		}
  	} else if (use_fxsr()) {
  		return fxrstor_user(buf);
  	} else
  		return frstor_user(buf);
  }
  
  int __restore_xstate_sig(void __user *buf, void __user *buf_fx, int size)
  {
  	int ia32_fxstate = (buf != buf_fx);
  	struct task_struct *tsk = current;
  	int state_size = xstate_size;
  	u64 xstate_bv = 0;
  	int fx_only = 0;
  
  	ia32_fxstate &= (config_enabled(CONFIG_X86_32) ||
  			 config_enabled(CONFIG_IA32_EMULATION));
  
  	if (!buf) {
  		drop_init_fpu(tsk);
  		return 0;
  	}
  
  	if (!access_ok(VERIFY_READ, buf, size))
  		return -EACCES;
  
  	if (!used_math() && init_fpu(tsk))
  		return -1;
  
  	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;
  			xstate_bv = fx_sw_user.xstate_bv;
  		}
  	}
  
  	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 used_math(). 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
  		 * set_used_math() is again set.
  		 */
  		drop_fpu(tsk);
  
  		if (__copy_from_user(&fpu->state->xsave, buf_fx, state_size) ||
  		    __copy_from_user(&env, buf, sizeof(env))) {
  			fpu_finit(fpu);
  			err = -1;
  		} else {
  			sanitize_restored_xstate(tsk, &env, xstate_bv, fx_only);
  		}
  
  		set_used_math();
  		if (use_eager_fpu()) {
  			preempt_disable();
  			math_state_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 (restore_user_xstate(buf_fx, xstate_bv, fx_only)) {
  			drop_init_fpu(tsk);
  			return -1;
  		}
  	}
  
  	return 0;
  }
  
  /*
   * 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.xstate_bv = pcntxt_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
   */
  static inline void xstate_enable(void)
  {
  	cr4_set_bits(X86_CR4_OSXSAVE);
  	xsetbv(XCR_XFEATURE_ENABLED_MASK, pcntxt_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;
  
  	xstate_features = fls64(pcntxt_mask);
  	xstate_offsets = alloc_bootmem(xstate_features * sizeof(int));
  	xstate_sizes = alloc_bootmem(xstate_features * sizeof(int));
  
  	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);
  }
  
  /*
   * 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(pcntxt_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 < xstate_features; i++) {
  			if (test_bit(i, (unsigned long *)&pcntxt_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 < xstate_features; i++) {
  		if (test_bit(i, (unsigned long *)&pcntxt_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 __init setup_init_fpu_buf(void)
  {
  	/*
  	 * Setup init_xstate_buf to represent the init state of
  	 * all the features managed by the xsave
  	 */
  	init_xstate_buf = alloc_bootmem_align(xstate_size,
  					      __alignof__(struct xsave_struct));
  	fx_finit(&init_xstate_buf->i387);
  
  	if (!cpu_has_xsave)
  		return;
  
  	setup_xstate_features();
  
  	if (cpu_has_xsaves) {
  		init_xstate_buf->xsave_hdr.xcomp_bv =
  						(u64)1 << 63 | pcntxt_mask;
  		init_xstate_buf->xsave_hdr.xstate_bv = pcntxt_mask;
  	}
  
  	/*
  	 * Init all the features state with header_bv being 0x0
  	 */
  	xrstor_state_booting(init_xstate_buf, -1);
  	/*
  	 * Dump the init state again. This is to identify the init state
  	 * of any feature which is not represented by all zero's.
  	 */
  	xsave_state_booting(init_xstate_buf, -1);
  }
  
  static enum { AUTO, ENABLE, DISABLE } eagerfpu = AUTO;
  static int __init eager_fpu_setup(char *s)
  {
  	if (!strcmp(s, "on"))
  		eagerfpu = ENABLE;
  	else if (!strcmp(s, "off"))
  		eagerfpu = DISABLE;
  	else if (!strcmp(s, "auto"))
  		eagerfpu = AUTO;
  	return 1;
  }
  __setup("eagerfpu=", eager_fpu_setup);
  
  
  /*
   * Calculate total size of enabled xstates in XCR0/pcntxt_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 *)&pcntxt_mask)) {
  			cpuid_count(XSTATE_CPUID, i, &eax, &ebx, &ecx, &edx);
  			xstate_size += eax;
  		}
  	}
  }
  
  /*
   * Enable and initialize the xsave feature.
   */
  static void __init xstate_enable_boot_cpu(void)
  {
  	unsigned int eax, ebx, ecx, edx;
  
  	if (boot_cpu_data.cpuid_level < XSTATE_CPUID) {
  		WARN(1, KERN_ERR "XSTATE_CPUID missing\n");
  		return;
  	}
  
  	cpuid_count(XSTATE_CPUID, 0, &eax, &ebx, &ecx, &edx);
  	pcntxt_mask = eax + ((u64)edx << 32);
  
  	if ((pcntxt_mask & XSTATE_FPSSE) != XSTATE_FPSSE) {
  		pr_err("FP/SSE not shown under xsave features 0x%llx\n",
  		       pcntxt_mask);
  		BUG();
  	}
  
  	/*
  	 * Support only the state known to OS.
  	 */
  	pcntxt_mask = pcntxt_mask & XCNTXT_MASK;
  
  	xstate_enable();
  
  	/*
  	 * Recompute the context size for enabled features
  	 */
  	init_xstate_size();
  
  	update_regset_xstate_info(xstate_size, pcntxt_mask);
  	prepare_fx_sw_frame();
  	setup_init_fpu_buf();
  
  	/* Auto enable eagerfpu for xsaveopt */
  	if (cpu_has_xsaveopt && eagerfpu != DISABLE)
  		eagerfpu = ENABLE;
  
  	if (pcntxt_mask & XSTATE_EAGER) {
  		if (eagerfpu == DISABLE) {
  			pr_err("eagerfpu not present, disabling some xstate features: 0x%llx\n",
  					pcntxt_mask & XSTATE_EAGER);
  			pcntxt_mask &= ~XSTATE_EAGER;
  		} else {
  			eagerfpu = ENABLE;
  		}
  	}
  
  	pr_info("enabled xstate_bv 0x%llx, cntxt size 0x%x using %s\n",
  		pcntxt_mask, xstate_size,
  		cpu_has_xsaves ? "compacted form" : "standard form");
  }
  
  /*
   * For the very first instance, this calls xstate_enable_boot_cpu();
   * for all subsequent instances, this calls xstate_enable().
   *
   * This is somewhat obfuscated due to the lack of powerful enough
   * overrides for the section checks.
   */
  void xsave_init(void)
  {
  	static __refdata void (*next_func)(void) = xstate_enable_boot_cpu;
  	void (*this_func)(void);
  
  	if (!cpu_has_xsave)
  		return;
  
  	this_func = next_func;
  	next_func = xstate_enable;
  	this_func();
  }
  
  static inline void __init eager_fpu_init_bp(void)
  {
  	current->thread.fpu.state =
  	    alloc_bootmem_align(xstate_size, __alignof__(struct xsave_struct));
  	if (!init_xstate_buf)
  		setup_init_fpu_buf();
  }
  
  void eager_fpu_init(void)
  {
  	static __refdata void (*boot_func)(void) = eager_fpu_init_bp;
  
  	clear_used_math();
  	current_thread_info()->status = 0;
  
  	if (eagerfpu == ENABLE)
  		setup_force_cpu_cap(X86_FEATURE_EAGER_FPU);
  
  	if (!cpu_has_eager_fpu) {
  		stts();
  		return;
  	}
  
  	if (boot_func) {
  		boot_func();
  		boot_func = NULL;
  	}
  
  	/*
  	 * This is same as math_state_restore(). But use_xsave() is
  	 * not yet patched to use math_state_restore().
  	 */
  	init_fpu(current);
  	__thread_fpu_begin(current);
  	if (cpu_has_xsave)
  		xrstor_state(init_xstate_buf, -1);
  	else
  		fxrstor_checking(&init_xstate_buf->i387);
  }
  
  /*
   * 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 *)&pcntxt_mask))
  		return NULL;
  
  	return (void *)xsave + xstate_comp_offsets[feature];
  }
  EXPORT_SYMBOL_GPL(get_xsave_addr);
  