8 * The legacy x87 FPU state format, as saved by FSAVE and
9 * restored by the FRSTOR instructions:
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 */
20 /* 8*10 bytes for each FP-reg = 80 bytes: */
23 /* Software status information [not touched by FSAVE]: */
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.
34 u16 cwd; /* Control Word */
35 u16 swd; /* Status Word */
36 u16 twd; /* Tag Word */
37 u16 fop; /* Last Instruction Opcode */
40 u64 rip; /* Instruction Pointer */
41 u64 rdp; /* Data Pointer */
44 u32 fip; /* FPU IP Offset */
45 u32 fcs; /* FPU IP Selector */
46 u32 foo; /* FPU Operand Offset */
47 u32 fos; /* FPU Operand Selector */
50 u32 mxcsr; /* MXCSR Register State */
51 u32 mxcsr_mask; /* MXCSR Mask */
53 /* 8*16 bytes for each FP-reg = 128 bytes: */
56 /* 16*16 bytes for each XMM-reg = 256 bytes: */
66 } __attribute__((aligned(16)));
68 /* Default value for fxregs_state.mxcsr: */
69 #define MXCSR_DEFAULT 0x1f80
72 * Software based FPU emulation state. This is arbitrary really,
73 * it matches the x87 format to make it easier to understand:
83 /* 8*10 bytes for each FP-reg = 80 bytes: */
91 struct math_emu_info *info;
96 * List of XSAVE features Linux knows about:
105 XSTATE_BIT_ZMM_Hi256,
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)
120 #define XSTATE_FPSSE (XSTATE_FP | XSTATE_SSE)
121 #define XSTATE_AVX512 (XSTATE_OPMASK | XSTATE_ZMM_Hi256 | XSTATE_Hi16_ZMM)
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[]'.
128 * The high 128 bits are stored here:
129 * 16x 128 bits == 256 bytes.
135 /* Intel MPX support: */
147 struct bndreg bndreg[4];
148 struct bndcsr bndcsr;
151 struct xstate_header {
155 } __attribute__((packed));
158 * This is our most modern FPU state format, as saved by the XSAVE
159 * and restored by the XRSTOR instructions.
161 * It consists of a legacy fxregs portion, an xstate header and
162 * subsequent areas as defined by the xstate header. Not all CPUs
163 * support all the extensions, so the size of the extended area
164 * can vary quite a bit between CPUs.
167 struct fxregs_state i387;
168 struct xstate_header header;
169 u8 extended_state_area[0];
170 } __attribute__ ((packed, aligned (64)));
173 * This is a union of all the possible FPU state formats
174 * put together, so that we can pick the right one runtime.
176 * The size of the structure is determined by the largest
177 * member - which is the xsave area. The padding is there
178 * to ensure that statically-allocated task_structs (just
179 * the init_task today) have enough space.
182 struct fregs_state fsave;
183 struct fxregs_state fxsave;
184 struct swregs_state soft;
185 struct xregs_state xsave;
186 u8 __padding[PAGE_SIZE];
190 * Highest level per task FPU state data structure that
191 * contains the FPU register state plus various FPU
198 * Records the last CPU on which this context was loaded into
199 * FPU registers. (In the lazy-restore case we might be
200 * able to reuse FPU registers across multiple context switches
201 * this way, if no intermediate task used the FPU.)
203 * A value of -1 is used to indicate that the FPU state in context
204 * memory is newer than the FPU state in registers, and that the
205 * FPU state should be reloaded next time the task is run.
207 unsigned int last_cpu;
212 * This flag indicates whether this context is active: if the task
213 * is not running then we can restore from this context, if the task
214 * is running then we should save into this context.
216 unsigned char fpstate_active;
221 * This flag determines whether a given context is actively
222 * loaded into the FPU's registers and that those registers
223 * represent the task's current FPU state.
225 * Note the interaction with fpstate_active:
227 * # task does not use the FPU:
228 * fpstate_active == 0
230 * # task uses the FPU and regs are active:
231 * fpstate_active == 1 && fpregs_active == 1
233 * # the regs are inactive but still match fpstate:
234 * fpstate_active == 1 && fpregs_active == 0 && fpregs_owner == fpu
236 * The third state is what we use for the lazy restore optimization
237 * on lazy-switching CPUs.
239 unsigned char fpregs_active;
244 * This counter contains the number of consecutive context switches
245 * during which the FPU stays used. If this is over a threshold, the
246 * lazy FPU restore logic becomes eager, to save the trap overhead.
247 * This is an unsigned char so that after 256 iterations the counter
248 * wraps and the context switch behavior turns lazy again; this is to
249 * deal with bursty apps that only use the FPU for a short time:
251 unsigned char counter;
255 * In-memory copy of all FPU registers that we save/restore
256 * over context switches. If the task is using the FPU then
257 * the registers in the FPU are more recent than this state
258 * copy. If the task context-switches away then they get
259 * saved here and represent the FPU state.
261 * After context switches there may be a (short) time period
262 * during which the in-FPU hardware registers are unchanged
263 * and still perfectly match this state, if the tasks
264 * scheduled afterwards are not using the FPU.
266 * This is the 'lazy restore' window of optimization, which
267 * we track though 'fpu_fpregs_owner_ctx' and 'fpu->last_cpu'.
269 * We detect whether a subsequent task uses the FPU via setting
270 * CR0::TS to 1, which causes any FPU use to raise a #NM fault.
272 * During this window, if the task gets scheduled again, we
273 * might be able to skip having to do a restore from this
274 * memory buffer to the hardware registers - at the cost of
275 * incurring the overhead of #NM fault traps.
277 * Note that on modern CPUs that support the XSAVEOPT (or other
278 * optimized XSAVE instructions), we don't use #NM traps anymore,
279 * as the hardware can track whether FPU registers need saving
280 * or not. On such CPUs we activate the non-lazy ('eagerfpu')
281 * logic, which unconditionally saves/restores all FPU state
282 * across context switches. (if FPU state exists.)
284 union fpregs_state state;
286 * WARNING: 'state' is dynamically-sized. Do not put
287 * anything after it here.
291 #endif /* _ASM_X86_FPU_H */