/* * xsave/xrstor support. * * Author: Suresh Siddha */ #include #include #include #include #include #include #include /* * Although we spell it out in here, the Processor Trace * xfeature is completely unused. We use other mechanisms * to save/restore PT state in Linux. */ 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" , "Processor Trace (unused)" , "Protection Keys User registers", "unknown xstate feature" , }; /* * Mask of xstate features supported by the CPU and the kernel: */ u64 xfeatures_mask __read_mostly; static unsigned int xstate_offsets[XFEATURE_MAX] = { [ 0 ... XFEATURE_MAX - 1] = -1}; static unsigned int xstate_sizes[XFEATURE_MAX] = { [ 0 ... XFEATURE_MAX - 1] = -1}; static unsigned int xstate_comp_offsets[sizeof(xfeatures_mask)*8]; /* * Clear all of the X86_FEATURE_* bits that are unavailable * when the CPU has no XSAVE support. */ void fpu__xstate_clear_all_cpu_caps(void) { setup_clear_cpu_cap(X86_FEATURE_XSAVE); setup_clear_cpu_cap(X86_FEATURE_XSAVEOPT); setup_clear_cpu_cap(X86_FEATURE_XSAVEC); setup_clear_cpu_cap(X86_FEATURE_XSAVES); setup_clear_cpu_cap(X86_FEATURE_AVX); setup_clear_cpu_cap(X86_FEATURE_AVX2); setup_clear_cpu_cap(X86_FEATURE_AVX512F); setup_clear_cpu_cap(X86_FEATURE_AVX512PF); setup_clear_cpu_cap(X86_FEATURE_AVX512ER); setup_clear_cpu_cap(X86_FEATURE_AVX512CD); setup_clear_cpu_cap(X86_FEATURE_MPX); setup_clear_cpu_cap(X86_FEATURE_XGETBV1); setup_clear_cpu_cap(X86_FEATURE_PKU); } /* * 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 "XFEATURE_MASK_SSE | XFEATURE_MASK_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 (or other optimized XSAVE instructions), 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 fxregs_state *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 & XFEATURE_MASK_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 & XFEATURE_MASK_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++; } } /* * 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); } /* * Note that in the future we will likely need a pair of * functions here: one for user xstates and the other for * system xstates. For now, they are the same. */ static int xfeature_enabled(enum xfeature xfeature) { return !!(xfeatures_mask & (1UL << xfeature)); } /* * Record the offsets and sizes of various xstates contained * in the XSAVE state memory layout. */ static void __init setup_xstate_features(void) { u32 eax, ebx, ecx, edx, i; /* start at the beginnning of the "extended state" */ unsigned int last_good_offset = offsetof(struct xregs_state, extended_state_area); for (i = FIRST_EXTENDED_XFEATURE; i < XFEATURE_MAX; i++) { if (!xfeature_enabled(i)) continue; cpuid_count(XSTATE_CPUID, i, &eax, &ebx, &ecx, &edx); xstate_offsets[i] = ebx; xstate_sizes[i] = eax; /* * In our xstate size checks, we assume that the * highest-numbered xstate feature has the * highest offset in the buffer. Ensure it does. */ WARN_ONCE(last_good_offset > xstate_offsets[i], "x86/fpu: misordered xstate at %d\n", last_good_offset); last_good_offset = xstate_offsets[i]; printk(KERN_INFO "x86/fpu: xstate_offset[%d]: %4d, xstate_sizes[%d]: %4d\n", i, ebx, i, eax); } } static void __init 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%03Lx: '%s'\n", xstate_mask, feature_name); } /* * Print out all the supported xstate features: */ static void __init print_xstate_features(void) { print_xstate_feature(XFEATURE_MASK_FP); print_xstate_feature(XFEATURE_MASK_SSE); print_xstate_feature(XFEATURE_MASK_YMM); print_xstate_feature(XFEATURE_MASK_BNDREGS); print_xstate_feature(XFEATURE_MASK_BNDCSR); print_xstate_feature(XFEATURE_MASK_OPMASK); print_xstate_feature(XFEATURE_MASK_ZMM_Hi256); print_xstate_feature(XFEATURE_MASK_Hi16_ZMM); print_xstate_feature(XFEATURE_MASK_PKRU); } /* * 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. */ static void __init 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 fxregs_state, xmm_space); if (!cpu_has_xsaves) { for (i = FIRST_EXTENDED_XFEATURE; i < XFEATURE_MAX; i++) { if (xfeature_enabled(i)) { xstate_comp_offsets[i] = xstate_offsets[i]; xstate_comp_sizes[i] = xstate_sizes[i]; } } return; } xstate_comp_offsets[FIRST_EXTENDED_XFEATURE] = FXSAVE_SIZE + XSAVE_HDR_SIZE; for (i = FIRST_EXTENDED_XFEATURE; i < XFEATURE_MAX; i++) { if (xfeature_enabled(i)) xstate_comp_sizes[i] = xstate_sizes[i]; else xstate_comp_sizes[i] = 0; if (i > FIRST_EXTENDED_XFEATURE) 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) { static int on_boot_cpu __initdata = 1; WARN_ON_FPU(!on_boot_cpu); on_boot_cpu = 0; 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); /* * 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); } static int xfeature_is_supervisor(int xfeature_nr) { /* * We currently do not support supervisor states, but if * we did, we could find out like this. * * SDM says: If state component i is a user state component, * ECX[0] return 0; if state component i is a supervisor * state component, ECX[0] returns 1. u32 eax, ebx, ecx, edx; cpuid_count(XSTATE_CPUID, xfeature_nr, &eax, &ebx, &ecx, &edx; return !!(ecx & 1); */ return 0; } /* static int xfeature_is_user(int xfeature_nr) { return !xfeature_is_supervisor(xfeature_nr); } */ /* * This check is important because it is easy to get XSTATE_* * confused with XSTATE_BIT_*. */ #define CHECK_XFEATURE(nr) do { \ WARN_ON(nr < FIRST_EXTENDED_XFEATURE); \ WARN_ON(nr >= XFEATURE_MAX); \ } while (0) /* * We could cache this like xstate_size[], but we only use * it here, so it would be a waste of space. */ static int xfeature_is_aligned(int xfeature_nr) { u32 eax, ebx, ecx, edx; CHECK_XFEATURE(xfeature_nr); cpuid_count(XSTATE_CPUID, xfeature_nr, &eax, &ebx, &ecx, &edx); /* * The value returned by ECX[1] indicates the alignment * of state component i when the compacted format * of the extended region of an XSAVE area is used */ return !!(ecx & 2); } static int xfeature_uncompacted_offset(int xfeature_nr) { u32 eax, ebx, ecx, edx; CHECK_XFEATURE(xfeature_nr); cpuid_count(XSTATE_CPUID, xfeature_nr, &eax, &ebx, &ecx, &edx); return ebx; } static int xfeature_size(int xfeature_nr) { u32 eax, ebx, ecx, edx; CHECK_XFEATURE(xfeature_nr); cpuid_count(XSTATE_CPUID, xfeature_nr, &eax, &ebx, &ecx, &edx); return eax; } /* * 'XSAVES' implies two different things: * 1. saving of supervisor/system state * 2. using the compacted format * * Use this function when dealing with the compacted format so * that it is obvious which aspect of 'XSAVES' is being handled * by the calling code. */ static int using_compacted_format(void) { return cpu_has_xsaves; } static void __xstate_dump_leaves(void) { int i; u32 eax, ebx, ecx, edx; static int should_dump = 1; if (!should_dump) return; should_dump = 0; /* * Dump out a few leaves past the ones that we support * just in case there are some goodies up there */ for (i = 0; i < XFEATURE_MAX + 10; i++) { cpuid_count(XSTATE_CPUID, i, &eax, &ebx, &ecx, &edx); pr_warn("CPUID[%02x, %02x]: eax=%08x ebx=%08x ecx=%08x edx=%08x\n", XSTATE_CPUID, i, eax, ebx, ecx, edx); } } #define XSTATE_WARN_ON(x) do { \ if (WARN_ONCE(x, "XSAVE consistency problem, dumping leaves")) { \ __xstate_dump_leaves(); \ } \ } while (0) #define XCHECK_SZ(sz, nr, nr_macro, __struct) do { \ if ((nr == nr_macro) && \ WARN_ONCE(sz != sizeof(__struct), \ "%s: struct is %zu bytes, cpu state %d bytes\n", \ __stringify(nr_macro), sizeof(__struct), sz)) { \ __xstate_dump_leaves(); \ } \ } while (0) /* * We have a C struct for each 'xstate'. We need to ensure * that our software representation matches what the CPU * tells us about the state's size. */ static void check_xstate_against_struct(int nr) { /* * Ask the CPU for the size of the state. */ int sz = xfeature_size(nr); /* * Match each CPU state with the corresponding software * structure. */ XCHECK_SZ(sz, nr, XFEATURE_YMM, struct ymmh_struct); XCHECK_SZ(sz, nr, XFEATURE_BNDREGS, struct mpx_bndreg_state); XCHECK_SZ(sz, nr, XFEATURE_BNDCSR, struct mpx_bndcsr_state); XCHECK_SZ(sz, nr, XFEATURE_OPMASK, struct avx_512_opmask_state); XCHECK_SZ(sz, nr, XFEATURE_ZMM_Hi256, struct avx_512_zmm_uppers_state); XCHECK_SZ(sz, nr, XFEATURE_Hi16_ZMM, struct avx_512_hi16_state); XCHECK_SZ(sz, nr, XFEATURE_PKRU, struct pkru_state); /* * Make *SURE* to add any feature numbers in below if * there are "holes" in the xsave state component * numbers. */ if ((nr < XFEATURE_YMM) || (nr >= XFEATURE_MAX) || (nr == XFEATURE_PT_UNIMPLEMENTED_SO_FAR)) { WARN_ONCE(1, "no structure for xstate: %d\n", nr); XSTATE_WARN_ON(1); } } /* * This essentially double-checks what the cpu told us about * how large the XSAVE buffer needs to be. We are recalculating * it to be safe. */ static void do_extra_xstate_size_checks(void) { int paranoid_xstate_size = FXSAVE_SIZE + XSAVE_HDR_SIZE; int i; for (i = FIRST_EXTENDED_XFEATURE; i < XFEATURE_MAX; i++) { if (!xfeature_enabled(i)) continue; check_xstate_against_struct(i); /* * Supervisor state components can be managed only by * XSAVES, which is compacted-format only. */ if (!using_compacted_format()) XSTATE_WARN_ON(xfeature_is_supervisor(i)); /* Align from the end of the previous feature */ if (xfeature_is_aligned(i)) paranoid_xstate_size = ALIGN(paranoid_xstate_size, 64); /* * The offset of a given state in the non-compacted * format is given to us in a CPUID leaf. We check * them for being ordered (increasing offsets) in * setup_xstate_features(). */ if (!using_compacted_format()) paranoid_xstate_size = xfeature_uncompacted_offset(i); /* * The compacted-format offset always depends on where * the previous state ended. */ paranoid_xstate_size += xfeature_size(i); } XSTATE_WARN_ON(paranoid_xstate_size != xstate_size); } /* * Calculate total size of enabled xstates in XCR0/xfeatures_mask. * * Note the SDM's wording here. "sub-function 0" only enumerates * the size of the *user* states. If we use it to size a buffer * that we use 'XSAVES' on, we could potentially overflow the * buffer because 'XSAVES' saves system states too. * * Note that we do not currently set any bits on IA32_XSS so * 'XCR0 | IA32_XSS == XCR0' for now. */ static unsigned int __init calculate_xstate_size(void) { unsigned int eax, ebx, ecx, edx; unsigned int calculated_xstate_size; if (!cpu_has_xsaves) { /* * - CPUID function 0DH, sub-function 0: * EBX enumerates the size (in bytes) required by * the XSAVE instruction for an XSAVE area * containing all the *user* state components * corresponding to bits currently set in XCR0. */ cpuid_count(XSTATE_CPUID, 0, &eax, &ebx, &ecx, &edx); calculated_xstate_size = ebx; } else { /* * - CPUID function 0DH, sub-function 1: * EBX enumerates the size (in bytes) required by * the XSAVES instruction for an XSAVE area * containing all the state components * corresponding to bits currently set in * XCR0 | IA32_XSS. */ cpuid_count(XSTATE_CPUID, 1, &eax, &ebx, &ecx, &edx); calculated_xstate_size = ebx; } return calculated_xstate_size; } /* * Will the runtime-enumerated 'xstate_size' fit in the init * task's statically-allocated buffer? */ static bool is_supported_xstate_size(unsigned int test_xstate_size) { if (test_xstate_size <= sizeof(union fpregs_state)) return true; pr_warn("x86/fpu: xstate buffer too small (%zu < %d), disabling xsave\n", sizeof(union fpregs_state), test_xstate_size); return false; } static int init_xstate_size(void) { /* Recompute the context size for enabled features: */ unsigned int possible_xstate_size = calculate_xstate_size(); /* Ensure we have the space to store all enabled: */ if (!is_supported_xstate_size(possible_xstate_size)) return -EINVAL; /* * The size is OK, we are definitely going to use xsave, * make it known to the world that we need more space. */ xstate_size = possible_xstate_size; do_extra_xstate_size_checks(); return 0; } /* * We enabled the XSAVE hardware, but something went wrong and * we can not use it. Disable it. */ static void fpu__init_disable_system_xstate(void) { xfeatures_mask = 0; cr4_clear_bits(X86_CR4_OSXSAVE); fpu__xstate_clear_all_cpu_caps(); } /* * Enable and initialize the xsave feature. * Called once per system bootup. */ void __init fpu__init_system_xstate(void) { unsigned int eax, ebx, ecx, edx; static int on_boot_cpu __initdata = 1; int err; WARN_ON_FPU(!on_boot_cpu); on_boot_cpu = 0; if (!cpu_has_xsave) { pr_info("x86/fpu: Legacy x87 FPU detected.\n"); return; } if (boot_cpu_data.cpuid_level < XSTATE_CPUID) { WARN_ON_FPU(1); return; } cpuid_count(XSTATE_CPUID, 0, &eax, &ebx, &ecx, &edx); xfeatures_mask = eax + ((u64)edx << 32); if ((xfeatures_mask & XFEATURE_MASK_FPSSE) != XFEATURE_MASK_FPSSE) { pr_err("x86/fpu: FP/SSE not present amongst the CPU's xstate features: 0x%llx.\n", xfeatures_mask); BUG(); } xfeatures_mask &= fpu__get_supported_xfeatures_mask(); /* Enable xstate instructions to be able to continue with initialization: */ fpu__init_cpu_xstate(); err = init_xstate_size(); if (err) { /* something went wrong, boot without any XSAVE support */ fpu__init_disable_system_xstate(); return; } update_regset_xstate_info(xstate_size, xfeatures_mask); fpu__init_prepare_fx_sw_frame(); setup_init_fpu_buf(); setup_xstate_comp(); pr_info("x86/fpu: Enabled xstate features 0x%llx, context size is %d 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 an xstate feature mask, calculate where in the xsave * buffer the state is. Callers should ensure that the buffer * is valid. * * Note: does not work for compacted buffers. */ void *__raw_xsave_addr(struct xregs_state *xsave, int xstate_feature_mask) { int feature_nr = fls64(xstate_feature_mask) - 1; return (void *)xsave + xstate_comp_offsets[feature_nr]; } /* * 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. * * Note that if there is no data for the field in the xsave buffer * this will return NULL. * * Inputs: * xstate: the thread's storage area for all FPU data * xstate_feature: state which is defined in xsave.h (e.g. * XFEATURE_MASK_FP, XFEATURE_MASK_SSE, etc...) * Output: * address of the state in the xsave area, or NULL if the * field is not present in the xsave buffer. */ void *get_xsave_addr(struct xregs_state *xsave, int xstate_feature) { /* * Do we even *have* xsave state? */ if (!boot_cpu_has(X86_FEATURE_XSAVE)) return NULL; /* * We should not ever be requesting features that we * have not enabled. Remember that pcntxt_mask is * what we write to the XCR0 register. */ WARN_ONCE(!(xfeatures_mask & xstate_feature), "get of unsupported state"); /* * This assumes the last 'xsave*' instruction to * have requested that 'xstate_feature' be saved. * If it did not, we might be seeing and old value * of the field in the buffer. * * This can happen because the last 'xsave' did not * request that this feature be saved (unlikely) * or because the "init optimization" caused it * to not be saved. */ if (!(xsave->header.xfeatures & xstate_feature)) return NULL; return __raw_xsave_addr(xsave, xstate_feature); } EXPORT_SYMBOL_GPL(get_xsave_addr); /* * This wraps up the common operations that need to occur when retrieving * data from xsave state. It first ensures that the current task was * using the FPU and retrieves the data in to a buffer. It then calculates * the offset of the requested field in the buffer. * * This function is safe to call whether the FPU is in use or not. * * Note that this only works on the current task. * * Inputs: * @xsave_state: state which is defined in xsave.h (e.g. XFEATURE_MASK_FP, * XFEATURE_MASK_SSE, etc...) * Output: * address of the state in the xsave area or NULL if the state * is not present or is in its 'init state'. */ const void *get_xsave_field_ptr(int xsave_state) { struct fpu *fpu = ¤t->thread.fpu; if (!fpu->fpstate_active) return NULL; /* * fpu__save() takes the CPU's xstate registers * and saves them off to the 'fpu memory buffer. */ fpu__save(fpu); return get_xsave_addr(&fpu->state.xsave, xsave_state); } /* * Set xfeatures (aka XSTATE_BV) bit for a feature that we want * to take out of its "init state". This will ensure that an * XRSTOR actually restores the state. */ static void fpu__xfeature_set_non_init(struct xregs_state *xsave, int xstate_feature_mask) { xsave->header.xfeatures |= xstate_feature_mask; } /* * This function is safe to call whether the FPU is in use or not. * * Note that this only works on the current task. * * Inputs: * @xsave_state: state which is defined in xsave.h (e.g. XFEATURE_MASK_FP, * XFEATURE_MASK_SSE, etc...) * @xsave_state_ptr: a pointer to a copy of the state that you would * like written in to the current task's FPU xsave state. This pointer * must not be located in the current tasks's xsave area. * Output: * address of the state in the xsave area or NULL if the state * is not present or is in its 'init state'. */ static void fpu__xfeature_set_state(int xstate_feature_mask, void *xstate_feature_src, size_t len) { struct xregs_state *xsave = ¤t->thread.fpu.state.xsave; struct fpu *fpu = ¤t->thread.fpu; void *dst; if (!boot_cpu_has(X86_FEATURE_XSAVE)) { WARN_ONCE(1, "%s() attempted with no xsave support", __func__); return; } /* * Tell the FPU code that we need the FPU state to be in * 'fpu' (not in the registers), and that we need it to * be stable while we write to it. */ fpu__current_fpstate_write_begin(); /* * This method *WILL* *NOT* work for compact-format * buffers. If the 'xstate_feature_mask' is unset in * xcomp_bv then we may need to move other feature state * "up" in the buffer. */ if (xsave->header.xcomp_bv & xstate_feature_mask) { WARN_ON_ONCE(1); goto out; } /* find the location in the xsave buffer of the desired state */ dst = __raw_xsave_addr(&fpu->state.xsave, xstate_feature_mask); /* * Make sure that the pointer being passed in did not * come from the xsave buffer itself. */ WARN_ONCE(xstate_feature_src == dst, "set from xsave buffer itself"); /* put the caller-provided data in the location */ memcpy(dst, xstate_feature_src, len); /* * Mark the xfeature so that the CPU knows there is state * in the buffer now. */ fpu__xfeature_set_non_init(xsave, xstate_feature_mask); out: /* * We are done writing to the 'fpu'. Reenable preeption * and (possibly) move the fpstate back in to the fpregs. */ fpu__current_fpstate_write_end(); }