// SPDX-License-Identifier: GPL-2.0-only
/*
 * x86 FPU boot time init code:
 */
#include <asm/fpu/api.h>
#include <asm/tlbflush.h>
#include <asm/setup.h>

#include <linux/sched.h>
#include <linux/sched/task.h>
#include <linux/init.h>

#include "internal.h"
#include "legacy.h"
#include "xstate.h"

/*
 * Initialize the registers found in all CPUs, CR0 and CR4:
 */
static void fpu__init_cpu_generic(void)
{
        unsigned long cr0;
        unsigned long cr4_mask = 0;

        if (boot_cpu_has(X86_FEATURE_FXSR))
                cr4_mask |= X86_CR4_OSFXSR;
        if (boot_cpu_has(X86_FEATURE_XMM))
                cr4_mask |= X86_CR4_OSXMMEXCPT;
        if (cr4_mask)
                cr4_set_bits(cr4_mask);

        cr0 = read_cr0();
        cr0 &= ~(X86_CR0_TS|X86_CR0_EM); /* clear TS and EM */
        if (!boot_cpu_has(X86_FEATURE_FPU))
                cr0 |= X86_CR0_EM;
        write_cr0(cr0);

        /* Flush out any pending x87 state: */
#ifdef CONFIG_MATH_EMULATION
        if (!boot_cpu_has(X86_FEATURE_FPU))
                ;
        else
#endif
                asm volatile ("fninit");
}

/*
 * Enable all supported FPU features. Called when a CPU is brought online:
 */
void fpu__init_cpu(void)
{
        fpu__init_cpu_generic();
        fpu__init_cpu_xstate();

        /* Start allowing kernel-mode FPU: */
        this_cpu_write(kernel_fpu_allowed, true);
}

static bool __init fpu__probe_without_cpuid(void)
{
        unsigned long cr0;
        u16 fsw, fcw;

        fsw = fcw = 0xffff;

        cr0 = read_cr0();
        cr0 &= ~(X86_CR0_TS | X86_CR0_EM);
        write_cr0(cr0);

        asm volatile("fninit ; fnstsw %0 ; fnstcw %1" : "+m" (fsw), "+m" (fcw));

        pr_info("x86/fpu: Probing for FPU: FSW=0x%04hx FCW=0x%04hx\n", fsw, fcw);

        return fsw == 0 && (fcw & 0x103f) == 0x003f;
}

static void __init fpu__init_system_early_generic(void)
{
        set_thread_flag(TIF_NEED_FPU_LOAD);

        if (!boot_cpu_has(X86_FEATURE_CPUID) &&
            !test_bit(X86_FEATURE_FPU, (unsigned long *)cpu_caps_cleared)) {
                if (fpu__probe_without_cpuid())
                        setup_force_cpu_cap(X86_FEATURE_FPU);
                else
                        setup_clear_cpu_cap(X86_FEATURE_FPU);
        }

#ifndef CONFIG_MATH_EMULATION
        if (!test_cpu_cap(&boot_cpu_data, X86_FEATURE_FPU)) {
                pr_emerg("x86/fpu: Giving up, no FPU found and no math emulation present\n");
                for (;;)
                        asm volatile("hlt");
        }
#endif
}

/*
 * Boot time FPU feature detection code:
 */
unsigned int mxcsr_feature_mask __ro_after_init = 0xffffffffu;

static void __init fpu__init_system_mxcsr(void)
{
        unsigned int mask = 0;

        if (boot_cpu_has(X86_FEATURE_FXSR)) {
                /* Static because GCC does not get 16-byte stack alignment right: */
                static struct fxregs_state fxregs __initdata;

                asm volatile("fxsave %0" : "+m" (fxregs));

                mask = fxregs.mxcsr_mask;

                /*
                 * If zero then use the default features mask,
                 * which has all features set, except the
                 * denormals-are-zero feature bit:
                 */
                if (mask == 0)
                        mask = 0x0000ffbf;
        }
        mxcsr_feature_mask &= mask;
}

/*
 * Once per bootup FPU initialization sequences that will run on most x86 CPUs:
 */
static void __init fpu__init_system_generic(void)
{
        /*
         * Set up the legacy init FPU context. Will be updated when the
         * CPU supports XSAVE[S].
         */
        fpstate_init_user(&init_fpstate);

        fpu__init_system_mxcsr();
}

/*
 * Enforce that 'MEMBER' is the last field of 'TYPE'.
 *
 * Align the computed size with alignment of the TYPE,
 * because that's how C aligns structs.
 */
#define CHECK_MEMBER_AT_END_OF(TYPE, MEMBER) \
        BUILD_BUG_ON(sizeof(TYPE) !=         \
                     ALIGN(offsetofend(TYPE, MEMBER), _Alignof(TYPE)))

/*
 * We append the 'struct fpu' to the task_struct:
 */
static void __init fpu__init_task_struct_size(void)
{
        int task_size = sizeof(struct task_struct);

        task_size += sizeof(struct fpu);

        /*
         * Subtract off the static size of the register state.
         * It potentially has a bunch of padding.
         */
        task_size -= sizeof(union fpregs_state);

        /*
         * Add back the dynamically-calculated register state
         * size.
         */
        task_size += fpu_kernel_cfg.default_size;

        /*
         * We dynamically size 'struct fpu', so we require that
         * 'state' be at the end of 'it:
         */
        CHECK_MEMBER_AT_END_OF(struct fpu, __fpstate);

        arch_task_struct_size = task_size;
}

/*
 * Set up the user and kernel xstate sizes based on the legacy FPU context size.
 *
 * We set this up first, and later it will be overwritten by
 * fpu__init_system_xstate() if the CPU knows about xstates.
 */
static void __init fpu__init_system_xstate_size_legacy(void)
{
        unsigned int size;

        /*
         * Note that the size configuration might be overwritten later
         * during fpu__init_system_xstate().
         */
        if (!cpu_feature_enabled(X86_FEATURE_FPU)) {
                size = sizeof(struct swregs_state);
        } else if (cpu_feature_enabled(X86_FEATURE_FXSR)) {
                size = sizeof(struct fxregs_state);
                fpu_user_cfg.legacy_features = XFEATURE_MASK_FPSSE;
        } else {
                size = sizeof(struct fregs_state);
                fpu_user_cfg.legacy_features = XFEATURE_MASK_FP;
        }

        fpu_kernel_cfg.max_size = size;
        fpu_kernel_cfg.default_size = size;
        fpu_user_cfg.max_size = size;
        fpu_user_cfg.default_size = size;
        guest_default_cfg.size = size;
}

/*
 * Called on the boot CPU once per system bootup, to set up the initial
 * FPU state that is later cloned into all processes:
 */
void __init fpu__init_system(void)
{
        fpu__init_system_early_generic();

        /*
         * The FPU has to be operational for some of the
         * later FPU init activities:
         */
        fpu__init_cpu();

        fpu__init_system_generic();
        fpu__init_system_xstate_size_legacy();
        fpu__init_system_xstate(fpu_kernel_cfg.max_size);
        fpu__init_task_struct_size();
}