arch/x86/kernel/xsave.c - maze/linux - Git at Google

 /*
  * xsave/xrstor support.
  *
  * Author: Suresh Siddha <suresh.b.siddha@intel.com>
  */
 #include <linux/bootmem.h>
 #include <linux/compat.h>
 #include <asm/i387.h>
 #include <asm/fpu-internal.h>
 #ifdef CONFIG_IA32_EMULATION
 #include <asm/sigcontext32.h>
 #endif
 #include <asm/xcr.h>

 /*
  * Supported feature mask by the CPU and the kernel.
  */
 u64 pcntxt_mask;

 /*
  * Represents init state for the supported extended state.
  */
 static struct xsave_struct *init_xstate_buf;

 struct _fpx_sw_bytes fx_sw_reserved;
 #ifdef CONFIG_IA32_EMULATION
 struct _fpx_sw_bytes fx_sw_reserved_ia32;
 #endif

 static unsigned int *xstate_offsets, *xstate_sizes, 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)
 {
 	u64 xstate_bv;
 	int feature_bit = 0x2;
 	struct i387_fxsave_struct *fx = &tsk->thread.fpu.state->fxsave;

 	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.
  */
 int check_for_xstate(struct i387_fxsave_struct __user *buf,
 		     void __user *fpstate,
 		     struct _fpx_sw_bytes *fx_sw_user)
 {
 	int min_xstate_size = sizeof(struct i387_fxsave_struct) +
 			      sizeof(struct xsave_hdr_struct);
 	unsigned int magic2;
 	int err;

 	err = __copy_from_user(fx_sw_user, &buf->sw_reserved[0],
 			       sizeof(struct _fpx_sw_bytes));
 	if (err)
 		return -EFAULT;

 	/*
 	 * First Magic check failed.
 	 */
 	if (fx_sw_user->magic1 != FP_XSTATE_MAGIC1)
 		return -EINVAL;

 	/*
 	 * Check for error scenarios.
 	 */
 	if (fx_sw_user->xstate_size < min_xstate_size ||
 	    fx_sw_user->xstate_size > xstate_size ||
 	    fx_sw_user->xstate_size > fx_sw_user->extended_size)
 		return -EINVAL;

 	err = __get_user(magic2, (__u32 *) (((void *)fpstate) +
 					    fx_sw_user->extended_size -
 					    FP_XSTATE_MAGIC2_SIZE));
 	if (err)
 		return err;
 	/*
 	 * 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 (magic2 != FP_XSTATE_MAGIC2)
 		return -EFAULT;

 	return 0;
 }

 #ifdef CONFIG_X86_64
 /*
  * Signal frame handlers.
  */

 int save_i387_xstate(void __user *buf)
 {
 	struct task_struct *tsk = current;
 	int err = 0;

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

 	BUG_ON(sig_xstate_size < xstate_size);

 	if ((unsigned long)buf % 64)
 		printk("save_i387_xstate: bad fpstate %p\n", buf);

 	if (!used_math())
 		return 0;

 	if (user_has_fpu()) {
 		if (use_xsave())
 			err = xsave_user(buf);
 		else
 			err = fxsave_user(buf);

 		if (err)
 			return err;
 		user_fpu_end();
 	} else {
 		sanitize_i387_state(tsk);
 		if (__copy_to_user(buf, &tsk->thread.fpu.state->fxsave,
 				   xstate_size))
 			return -1;
 	}

 	clear_used_math(); /* trigger finit */

 	if (use_xsave()) {
 		struct _fpstate __user *fx = buf;
 		struct _xstate __user *x = buf;
 		u64 xstate_bv;

 		err = __copy_to_user(&fx->sw_reserved, &fx_sw_reserved,
 				     sizeof(struct _fpx_sw_bytes));

 		err |= __put_user(FP_XSTATE_MAGIC2,
 				  (__u32 __user *) (buf + sig_xstate_size
 						    - FP_XSTATE_MAGIC2_SIZE));

 		/*
 		 * Read the xstate_bv which we copied (directly from the cpu or
 		 * from the state in task struct) to the user buffers and
 		 * set the FP/SSE bits.
 		 */
 		err |= __get_user(xstate_bv, &x->xstate_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, &x->xstate_hdr.xstate_bv);

 		if (err)
 			return err;
 	}

 	return 1;
 }

 /*
  * Restore the extended state if present. Otherwise, restore the FP/SSE
  * state.
  */
 static int restore_user_xstate(void __user *buf)
 {
 	struct _fpx_sw_bytes fx_sw_user;
 	u64 mask;
 	int err;

 	if (((unsigned long)buf % 64) ||
 	     check_for_xstate(buf, buf, &fx_sw_user))
 		goto fx_only;

 	mask = fx_sw_user.xstate_bv;

 	/*
 	 * restore the state passed by the user.
 	 */
 	err = xrestore_user(buf, mask);
 	if (err)
 		return err;

 	/*
 	 * init the state skipped by the user.
 	 */
 	mask = pcntxt_mask & ~mask;
 	if (unlikely(mask))
 		xrstor_state(init_xstate_buf, mask);

 	return 0;

 fx_only:
 	/*
 	 * couldn't find the extended state information in the
 	 * memory layout. Restore just the FP/SSE and init all
 	 * the other extended state.
 	 */
 	xrstor_state(init_xstate_buf, pcntxt_mask & ~XSTATE_FPSSE);
 	return fxrstor_checking((__force struct i387_fxsave_struct *)buf);
 }

 /*
  * This restores directly out of user space. Exceptions are handled.
  */
 int restore_i387_xstate(void __user *buf)
 {
 	struct task_struct *tsk = current;
 	int err = 0;

 	if (!buf) {
 		if (used_math())
 			goto clear;
 		return 0;
 	} else
 		if (!access_ok(VERIFY_READ, buf, sig_xstate_size))
 			return -EACCES;

 	if (!used_math()) {
 		err = init_fpu(tsk);
 		if (err)
 			return err;
 	}

 	user_fpu_begin();
 	if (use_xsave())
 		err = restore_user_xstate(buf);
 	else
 		err = fxrstor_checking((__force struct i387_fxsave_struct *)
 				       buf);
 	if (unlikely(err)) {
 		/*
 		 * Encountered an error while doing the restore from the
 		 * user buffer, clear the fpu state.
 		 */
 clear:
 		clear_fpu(tsk);
 		clear_used_math();
 	}
 	return err;
 }
 #endif

 /*
  * 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 size_extended = (xstate_size - sizeof(struct i387_fxsave_struct)) +
 			     FP_XSTATE_MAGIC2_SIZE;

 	sig_xstate_size = sizeof(struct _fpstate) + size_extended;

 #ifdef CONFIG_IA32_EMULATION
 	sig_xstate_ia32_size = sizeof(struct _fpstate_ia32) + size_extended;
 #endif

 	memset(&fx_sw_reserved, 0, sizeof(fx_sw_reserved));

 	fx_sw_reserved.magic1 = FP_XSTATE_MAGIC1;
 	fx_sw_reserved.extended_size = sig_xstate_size;
 	fx_sw_reserved.xstate_bv = pcntxt_mask;
 	fx_sw_reserved.xstate_size = xstate_size;
 #ifdef CONFIG_IA32_EMULATION
 	memcpy(&fx_sw_reserved_ia32, &fx_sw_reserved,
 	       sizeof(struct _fpx_sw_bytes));
 	fx_sw_reserved_ia32.extended_size = sig_xstate_ia32_size;
 #endif
 }

 #ifdef CONFIG_X86_64
 unsigned int sig_xstate_size = sizeof(struct _fpstate);
 #endif

 /*
  * Enable the extended processor state save/restore feature
  */
 static inline void xstate_enable(void)
 {
 	set_in_cr4(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);
 }

 /*
  * setup the xstate image representing the init state
  */
 static void __init setup_xstate_init(void)
 {
 	setup_xstate_features();

 	/*
 	 * 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));
 	init_xstate_buf->i387.mxcsr = MXCSR_DEFAULT;

 	clts();
 	/*
 	 * Init all the features state with header_bv being 0x0
 	 */
 	xrstor_state(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(init_xstate_buf, -1);
 	stts();
 }

 /*
  * 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) {
 		printk(KERN_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
 	 */
 	cpuid_count(XSTATE_CPUID, 0, &eax, &ebx, &ecx, &edx);
 	xstate_size = ebx;

 	update_regset_xstate_info(xstate_size, pcntxt_mask);
 	prepare_fx_sw_frame();

 	setup_xstate_init();

 	printk(KERN_INFO "xsave/xrstor: enabled xstate_bv 0x%llx, "
 	       "cntxt size 0x%x\n",
 	       pcntxt_mask, xstate_size);
 }

 /*
  * 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 __cpuinit 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();
 }
	/*
	* xsave/xrstor support.
	*
	* Author: Suresh Siddha <suresh.b.siddha@intel.com>
	*/
	#include <linux/bootmem.h>
	#include <linux/compat.h>
	#include <asm/i387.h>
	#include <asm/fpu-internal.h>
	#ifdef CONFIG_IA32_EMULATION
	#include <asm/sigcontext32.h>
	#endif
	#include <asm/xcr.h>

	/*
	* Supported feature mask by the CPU and the kernel.
	*/
	u64 pcntxt_mask;

	/*
	* Represents init state for the supported extended state.
	*/
	static struct xsave_struct *init_xstate_buf;

	struct _fpx_sw_bytes fx_sw_reserved;
	#ifdef CONFIG_IA32_EMULATION
	struct _fpx_sw_bytes fx_sw_reserved_ia32;
	#endif

	static unsigned int xstate_offsets, xstate_sizes, 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)
	{
	u64 xstate_bv;
	int feature_bit = 0x2;
	struct i387_fxsave_struct *fx = &tsk->thread.fpu.state->fxsave;

	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.
	*/
	int check_for_xstate(struct i387_fxsave_struct __user *buf,
	void __user *fpstate,
	struct _fpx_sw_bytes *fx_sw_user)
	{
	int min_xstate_size = sizeof(struct i387_fxsave_struct) +
	sizeof(struct xsave_hdr_struct);
	unsigned int magic2;
	int err;

	err = __copy_from_user(fx_sw_user, &buf->sw_reserved[0],
	sizeof(struct _fpx_sw_bytes));
	if (err)
	return -EFAULT;

	/*
	* First Magic check failed.
	*/
	if (fx_sw_user->magic1 != FP_XSTATE_MAGIC1)
	return -EINVAL;

	/*
	* Check for error scenarios.
	*/
	if (fx_sw_user->xstate_size < min_xstate_size \|\|
	fx_sw_user->xstate_size > xstate_size \|\|
	fx_sw_user->xstate_size > fx_sw_user->extended_size)
	return -EINVAL;

	err = __get_user(magic2, (__u32 ) (((void )fpstate) +
	fx_sw_user->extended_size -
	FP_XSTATE_MAGIC2_SIZE));
	if (err)
	return err;
	/*
	* 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 (magic2 != FP_XSTATE_MAGIC2)
	return -EFAULT;

	return 0;
	}

	#ifdef CONFIG_X86_64
	/*
	* Signal frame handlers.
	*/

	int save_i387_xstate(void __user *buf)
	{
	struct task_struct *tsk = current;
	int err = 0;

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

	BUG_ON(sig_xstate_size < xstate_size);

	if ((unsigned long)buf % 64)
	printk("save_i387_xstate: bad fpstate %p\n", buf);

	if (!used_math())
	return 0;

	if (user_has_fpu()) {
	if (use_xsave())
	err = xsave_user(buf);
	else
	err = fxsave_user(buf);

	if (err)
	return err;
	user_fpu_end();
	} else {
	sanitize_i387_state(tsk);
	if (__copy_to_user(buf, &tsk->thread.fpu.state->fxsave,
	xstate_size))
	return -1;
	}

	clear_used_math(); /* trigger finit */

	if (use_xsave()) {
	struct _fpstate __user *fx = buf;
	struct _xstate __user *x = buf;
	u64 xstate_bv;

	err = __copy_to_user(&fx->sw_reserved, &fx_sw_reserved,
	sizeof(struct _fpx_sw_bytes));

	err \|= __put_user(FP_XSTATE_MAGIC2,
	(__u32 __user *) (buf + sig_xstate_size
	- FP_XSTATE_MAGIC2_SIZE));

	/*
	* Read the xstate_bv which we copied (directly from the cpu or
	* from the state in task struct) to the user buffers and
	* set the FP/SSE bits.
	*/
	err \|= __get_user(xstate_bv, &x->xstate_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, &x->xstate_hdr.xstate_bv);

	if (err)
	return err;
	}

	return 1;
	}

	/*
	* Restore the extended state if present. Otherwise, restore the FP/SSE
	* state.
	*/
	static int restore_user_xstate(void __user *buf)
	{
	struct _fpx_sw_bytes fx_sw_user;
	u64 mask;
	int err;

	if (((unsigned long)buf % 64) \|\|
	check_for_xstate(buf, buf, &fx_sw_user))
	goto fx_only;

	mask = fx_sw_user.xstate_bv;

	/*
	* restore the state passed by the user.
	*/
	err = xrestore_user(buf, mask);
	if (err)
	return err;

	/*
	* init the state skipped by the user.
	*/
	mask = pcntxt_mask & ~mask;
	if (unlikely(mask))
	xrstor_state(init_xstate_buf, mask);

	return 0;

	fx_only:
	/*
	* couldn't find the extended state information in the
	* memory layout. Restore just the FP/SSE and init all
	* the other extended state.
	*/
	xrstor_state(init_xstate_buf, pcntxt_mask & ~XSTATE_FPSSE);
	return fxrstor_checking((__force struct i387_fxsave_struct *)buf);
	}

	/*
	* This restores directly out of user space. Exceptions are handled.
	*/
	int restore_i387_xstate(void __user *buf)
	{
	struct task_struct *tsk = current;
	int err = 0;

	if (!buf) {
	if (used_math())
	goto clear;
	return 0;
	} else
	if (!access_ok(VERIFY_READ, buf, sig_xstate_size))
	return -EACCES;

	if (!used_math()) {
	err = init_fpu(tsk);
	if (err)
	return err;
	}

	user_fpu_begin();
	if (use_xsave())
	err = restore_user_xstate(buf);
	else
	err = fxrstor_checking((__force struct i387_fxsave_struct *)
	buf);
	if (unlikely(err)) {
	/*
	* Encountered an error while doing the restore from the
	* user buffer, clear the fpu state.
	*/
	clear:
	clear_fpu(tsk);
	clear_used_math();
	}
	return err;
	}
	#endif

	/*
	* 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 size_extended = (xstate_size - sizeof(struct i387_fxsave_struct)) +
	FP_XSTATE_MAGIC2_SIZE;

	sig_xstate_size = sizeof(struct _fpstate) + size_extended;

	#ifdef CONFIG_IA32_EMULATION
	sig_xstate_ia32_size = sizeof(struct _fpstate_ia32) + size_extended;
	#endif

	memset(&fx_sw_reserved, 0, sizeof(fx_sw_reserved));

	fx_sw_reserved.magic1 = FP_XSTATE_MAGIC1;
	fx_sw_reserved.extended_size = sig_xstate_size;
	fx_sw_reserved.xstate_bv = pcntxt_mask;
	fx_sw_reserved.xstate_size = xstate_size;
	#ifdef CONFIG_IA32_EMULATION
	memcpy(&fx_sw_reserved_ia32, &fx_sw_reserved,
	sizeof(struct _fpx_sw_bytes));
	fx_sw_reserved_ia32.extended_size = sig_xstate_ia32_size;
	#endif
	}

	#ifdef CONFIG_X86_64
	unsigned int sig_xstate_size = sizeof(struct _fpstate);
	#endif

	/*
	* Enable the extended processor state save/restore feature
	*/
	static inline void xstate_enable(void)
	{
	set_in_cr4(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);
	}

	/*
	* setup the xstate image representing the init state
	*/
	static void __init setup_xstate_init(void)
	{
	setup_xstate_features();

	/*
	* 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));
	init_xstate_buf->i387.mxcsr = MXCSR_DEFAULT;

	clts();
	/*
	* Init all the features state with header_bv being 0x0
	*/
	xrstor_state(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(init_xstate_buf, -1);
	stts();
	}

	/*
	* 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) {
	printk(KERN_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
	*/
	cpuid_count(XSTATE_CPUID, 0, &eax, &ebx, &ecx, &edx);
	xstate_size = ebx;

	update_regset_xstate_info(xstate_size, pcntxt_mask);
	prepare_fx_sw_frame();

	setup_xstate_init();

	printk(KERN_INFO "xsave/xrstor: enabled xstate_bv 0x%llx, "
	"cntxt size 0x%x\n",
	pcntxt_mask, xstate_size);
	}

	/*
	* 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 __cpuinit 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();
	}