arch/x86/include/asm/fpu/types.h

   1 /*
   2  * FPU data structures:
   3  */
   4 #ifndef _ASM_X86_FPU_H
   5 #define _ASM_X86_FPU_H
   6
   7 /*
   8  * The legacy x87 FPU state format, as saved by FSAVE and
   9  * restored by the FRSTOR instructions:
  10  */
  11 struct fregs_state {
  12         u32                     cwd;    /* FPU Control Word             */
  13         u32                     swd;    /* FPU Status Word              */
  14         u32                     twd;    /* FPU Tag Word                 */
  15         u32                     fip;    /* FPU IP Offset                */
  16         u32                     fcs;    /* FPU IP Selector              */
  17         u32                     foo;    /* FPU Operand Pointer Offset   */
  18         u32                     fos;    /* FPU Operand Pointer Selector */
  19
  20         /* 8*10 bytes for each FP-reg = 80 bytes:                       */
  21         u32                     st_space[20];
  22
  23         /* Software status information [not touched by FSAVE]:          */
  24         u32                     status;
  25 };
  26
  27 /*
  28  * The legacy fx SSE/MMX FPU state format, as saved by FXSAVE and
  29  * restored by the FXRSTOR instructions. It's similar to the FSAVE
  30  * format, but differs in some areas, plus has extensions at
  31  * the end for the XMM registers.
  32  */
  33 struct fxregs_state {
  34         u16                     cwd; /* Control Word                    */
  35         u16                     swd; /* Status Word                     */
  36         u16                     twd; /* Tag Word                        */
  37         u16                     fop; /* Last Instruction Opcode         */
  38         union {
  39                 struct {
  40                         u64     rip; /* Instruction Pointer             */
  41                         u64     rdp; /* Data Pointer                    */
  42                 };
  43                 struct {
  44                         u32     fip; /* FPU IP Offset                   */
  45                         u32     fcs; /* FPU IP Selector                 */
  46                         u32     foo; /* FPU Operand Offset              */
  47                         u32     fos; /* FPU Operand Selector            */
  48                 };
  49         };
  50         u32                     mxcsr;          /* MXCSR Register State */
  51         u32                     mxcsr_mask;     /* MXCSR Mask           */
  52
  53         /* 8*16 bytes for each FP-reg = 128 bytes:                      */
  54         u32                     st_space[32];
  55
  56         /* 16*16 bytes for each XMM-reg = 256 bytes:                    */
  57         u32                     xmm_space[64];
  58
  59         u32                     padding[12];
  60
  61         union {
  62                 u32             padding1[12];
  63                 u32             sw_reserved[12];
  64         };
  65
  66 } __attribute__((aligned(16)));
  67
  68 /* Default value for fxregs_state.mxcsr: */
  69 #define MXCSR_DEFAULT           0x1f80
  70
  71 /*
  72  * Software based FPU emulation state. This is arbitrary really,
  73  * it matches the x87 format to make it easier to understand:
  74  */
  75 struct swregs_state {
  76         u32                     cwd;
  77         u32                     swd;
  78         u32                     twd;
  79         u32                     fip;
  80         u32                     fcs;
  81         u32                     foo;
  82         u32                     fos;
  83         /* 8*10 bytes for each FP-reg = 80 bytes: */
  84         u32                     st_space[20];
  85         u8                      ftop;
  86         u8                      changed;
  87         u8                      lookahead;
  88         u8                      no_update;
  89         u8                      rm;
  90         u8                      alimit;
  91         struct math_emu_info    *info;
  92         u32                     entry_eip;
  93 };
  94
  95 /*
  96  * List of XSAVE features Linux knows about:
  97  */
  98 enum xfeature_bit {
  99         XSTATE_BIT_FP,
 100         XSTATE_BIT_SSE,
 101         XSTATE_BIT_YMM,
 102         XSTATE_BIT_BNDREGS,
 103         XSTATE_BIT_BNDCSR,
 104         XSTATE_BIT_OPMASK,
 105         XSTATE_BIT_ZMM_Hi256,
 106         XSTATE_BIT_Hi16_ZMM,
 107
 108         XFEATURES_NR_MAX,
 109 };
 110
 111 #define XSTATE_FP               (1 << XSTATE_BIT_FP)
 112 #define XSTATE_SSE              (1 << XSTATE_BIT_SSE)
 113 #define XSTATE_YMM              (1 << XSTATE_BIT_YMM)
 114 #define XSTATE_BNDREGS          (1 << XSTATE_BIT_BNDREGS)
 115 #define XSTATE_BNDCSR           (1 << XSTATE_BIT_BNDCSR)
 116 #define XSTATE_OPMASK           (1 << XSTATE_BIT_OPMASK)
 117 #define XSTATE_ZMM_Hi256        (1 << XSTATE_BIT_ZMM_Hi256)
 118 #define XSTATE_Hi16_ZMM         (1 << XSTATE_BIT_Hi16_ZMM)
 119
 120 #define XSTATE_FPSSE            (XSTATE_FP | XSTATE_SSE)
 121 #define XSTATE_AVX512           (XSTATE_OPMASK | XSTATE_ZMM_Hi256 | XSTATE_Hi16_ZMM)
 122
 123 /*
 124  * There are 16x 256-bit AVX registers named YMM0-YMM15.
 125  * The low 128 bits are aliased to the 16 SSE registers (XMM0-XMM15)
 126  * and are stored in 'struct fxregs_state::xmm_space[]'.
 127  *
 128  * The high 128 bits are stored here:
 129  *    16x 128 bits == 256 bytes.
 130  */
 131 struct ymmh_struct {
 132         u8                              ymmh_space[256];
 133 };
 134
 135 /* We don't support LWP yet: */
 136 struct lwp_struct {
 137         u8                              reserved[128];
 138 };
 139
 140 /* Intel MPX support: */
 141 struct bndreg {
 142         u64                             lower_bound;
 143         u64                             upper_bound;
 144 } __packed;
 145
 146 struct bndcsr {
 147         u64                             bndcfgu;
 148         u64                             bndstatus;
 149 } __packed;
 150
 151 struct mpx_struct {
 152         struct bndreg                   bndreg[4];
 153         struct bndcsr                   bndcsr;
 154 };
 155
 156 struct xstate_header {
 157         u64                             xfeatures;
 158         u64                             xcomp_bv;
 159         u64                             reserved[6];
 160 } __attribute__((packed));
 161
 162 /* New processor state extensions should be added here: */
 163 #define XSTATE_RESERVE                  (sizeof(struct ymmh_struct) + \
 164                                          sizeof(struct lwp_struct)  + \
 165                                          sizeof(struct mpx_struct)  )
 166 /*
 167  * This is our most modern FPU state format, as saved by the XSAVE
 168  * and restored by the XRSTOR instructions.
 169  *
 170  * It consists of a legacy fxregs portion, an xstate header and
 171  * subsequent fixed size areas as defined by the xstate header.
 172  * Not all CPUs support all the extensions.
 173  */
 174 struct xregs_state {
 175         struct fxregs_state             i387;
 176         struct xstate_header            header;
 177         u8                              __reserved[XSTATE_RESERVE];
 178 } __attribute__ ((packed, aligned (64)));
 179
 180 /*
 181  * This is a union of all the possible FPU state formats
 182  * put together, so that we can pick the right one runtime.
 183  *
 184  * The size of the structure is determined by the largest
 185  * member - which is the xsave area:
 186  */
 187 union fpregs_state {
 188         struct fregs_state              fsave;
 189         struct fxregs_state             fxsave;
 190         struct swregs_state             soft;
 191         struct xregs_state              xsave;
 192 };
 193
 194 /*
 195  * Highest level per task FPU state data structure that
 196  * contains the FPU register state plus various FPU
 197  * state fields:
 198  */
 199 struct fpu {
 200         /*
 201          * @state:
 202          *
 203          * In-memory copy of all FPU registers that we save/restore
 204          * over context switches. If the task is using the FPU then
 205          * the registers in the FPU are more recent than this state
 206          * copy. If the task context-switches away then they get
 207          * saved here and represent the FPU state.
 208          *
 209          * After context switches there may be a (short) time period
 210          * during which the in-FPU hardware registers are unchanged
 211          * and still perfectly match this state, if the tasks
 212          * scheduled afterwards are not using the FPU.
 213          *
 214          * This is the 'lazy restore' window of optimization, which
 215          * we track though 'fpu_fpregs_owner_ctx' and 'fpu->last_cpu'.
 216          *
 217          * We detect whether a subsequent task uses the FPU via setting
 218          * CR0::TS to 1, which causes any FPU use to raise a #NM fault.
 219          *
 220          * During this window, if the task gets scheduled again, we
 221          * might be able to skip having to do a restore from this
 222          * memory buffer to the hardware registers - at the cost of
 223          * incurring the overhead of #NM fault traps.
 224          *
 225          * Note that on modern CPUs that support the XSAVEOPT (or other
 226          * optimized XSAVE instructions), we don't use #NM traps anymore,
 227          * as the hardware can track whether FPU registers need saving
 228          * or not. On such CPUs we activate the non-lazy ('eagerfpu')
 229          * logic, which unconditionally saves/restores all FPU state
 230          * across context switches. (if FPU state exists.)
 231          */
 232         union fpregs_state              state;
 233
 234         /*
 235          * @last_cpu:
 236          *
 237          * Records the last CPU on which this context was loaded into
 238          * FPU registers. (In the lazy-restore case we might be
 239          * able to reuse FPU registers across multiple context switches
 240          * this way, if no intermediate task used the FPU.)
 241          *
 242          * A value of -1 is used to indicate that the FPU state in context
 243          * memory is newer than the FPU state in registers, and that the
 244          * FPU state should be reloaded next time the task is run.
 245          */
 246         unsigned int                    last_cpu;
 247
 248         /*
 249          * @fpstate_active:
 250          *
 251          * This flag indicates whether this context is active: if the task
 252          * is not running then we can restore from this context, if the task
 253          * is running then we should save into this context.
 254          */
 255         unsigned char                   fpstate_active;
 256
 257         /*
 258          * @fpregs_active:
 259          *
 260          * This flag determines whether a given context is actively
 261          * loaded into the FPU's registers and that those registers
 262          * represent the task's current FPU state.
 263          *
 264          * Note the interaction with fpstate_active:
 265          *
 266          *   # task does not use the FPU:
 267          *   fpstate_active == 0
 268          *
 269          *   # task uses the FPU and regs are active:
 270          *   fpstate_active == 1 && fpregs_active == 1
 271          *
 272          *   # the regs are inactive but still match fpstate:
 273          *   fpstate_active == 1 && fpregs_active == 0 && fpregs_owner == fpu
 274          *
 275          * The third state is what we use for the lazy restore optimization
 276          * on lazy-switching CPUs.
 277          */
 278         unsigned char                   fpregs_active;
 279
 280         /*
 281          * @counter:
 282          *
 283          * This counter contains the number of consecutive context switches
 284          * during which the FPU stays used. If this is over a threshold, the
 285          * lazy FPU restore logic becomes eager, to save the trap overhead.
 286          * This is an unsigned char so that after 256 iterations the counter
 287          * wraps and the context switch behavior turns lazy again; this is to
 288          * deal with bursty apps that only use the FPU for a short time:
 289          */
 290         unsigned char                   counter;
 291 };
 292
 293 #endif /* _ASM_X86_FPU_H */