x86: Rewrite ret_from_fork() in C

[platform/kernel/linux-starfive.git] / arch / x86 / kernel / process.c

// SPDX-License-Identifier: GPL-2.0
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/errno.h>
#include <linux/kernel.h>
#include <linux/mm.h>
#include <linux/smp.h>
#include <linux/cpu.h>
#include <linux/prctl.h>
#include <linux/slab.h>
#include <linux/sched.h>
#include <linux/sched/idle.h>
#include <linux/sched/debug.h>
#include <linux/sched/task.h>
#include <linux/sched/task_stack.h>
#include <linux/init.h>
#include <linux/export.h>
#include <linux/pm.h>
#include <linux/tick.h>
#include <linux/random.h>
#include <linux/user-return-notifier.h>
#include <linux/dmi.h>
#include <linux/utsname.h>
#include <linux/stackprotector.h>
#include <linux/cpuidle.h>
#include <linux/acpi.h>
#include <linux/elf-randomize.h>
#include <linux/static_call.h>
#include <trace/events/power.h>
#include <linux/hw_breakpoint.h>
#include <linux/entry-common.h>
#include <asm/cpu.h>
#include <asm/apic.h>
#include <linux/uaccess.h>
#include <asm/mwait.h>
#include <asm/fpu/api.h>
#include <asm/fpu/sched.h>
#include <asm/fpu/xstate.h>
#include <asm/debugreg.h>
#include <asm/nmi.h>
#include <asm/tlbflush.h>
#include <asm/mce.h>
#include <asm/vm86.h>
#include <asm/switch_to.h>
#include <asm/desc.h>
#include <asm/prctl.h>
#include <asm/spec-ctrl.h>
#include <asm/io_bitmap.h>
#include <asm/proto.h>
#include <asm/frame.h>
#include <asm/unwind.h>
#include <asm/tdx.h>
#include <asm/mmu_context.h>

#include "process.h"

/*
 * per-CPU TSS segments. Threads are completely 'soft' on Linux,
 * no more per-task TSS's. The TSS size is kept cacheline-aligned
 * so they are allowed to end up in the .data..cacheline_aligned
 * section. Since TSS's are completely CPU-local, we want them
 * on exact cacheline boundaries, to eliminate cacheline ping-pong.
 */
__visible DEFINE_PER_CPU_PAGE_ALIGNED(struct tss_struct, cpu_tss_rw) = {
        .x86_tss = {
                /*
                 * .sp0 is only used when entering ring 0 from a lower
                 * privilege level.  Since the init task never runs anything
                 * but ring 0 code, there is no need for a valid value here.
                 * Poison it.
                 */
                .sp0 = (1UL << (BITS_PER_LONG-1)) + 1,

#ifdef CONFIG_X86_32
                .sp1 = TOP_OF_INIT_STACK,

                .ss0 = __KERNEL_DS,
                .ss1 = __KERNEL_CS,
#endif
                .io_bitmap_base = IO_BITMAP_OFFSET_INVALID,
         },
};
EXPORT_PER_CPU_SYMBOL(cpu_tss_rw);

DEFINE_PER_CPU(bool, __tss_limit_invalid);
EXPORT_PER_CPU_SYMBOL_GPL(__tss_limit_invalid);

/*
 * this gets called so that we can store lazy state into memory and copy the
 * current task into the new thread.
 */
int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src)
{
        memcpy(dst, src, arch_task_struct_size);
#ifdef CONFIG_VM86
        dst->thread.vm86 = NULL;
#endif
        /* Drop the copied pointer to current's fpstate */
        dst->thread.fpu.fpstate = NULL;

        return 0;
}

#ifdef CONFIG_X86_64
void arch_release_task_struct(struct task_struct *tsk)
{
        if (fpu_state_size_dynamic())
                fpstate_free(&tsk->thread.fpu);
}
#endif

/*
 * Free thread data structures etc..
 */
void exit_thread(struct task_struct *tsk)
{
        struct thread_struct *t = &tsk->thread;
        struct fpu *fpu = &t->fpu;

        if (test_thread_flag(TIF_IO_BITMAP))
                io_bitmap_exit(tsk);

        free_vm86(t);

        fpu__drop(fpu);
}

static int set_new_tls(struct task_struct *p, unsigned long tls)
{
        struct user_desc __user *utls = (struct user_desc __user *)tls;

        if (in_ia32_syscall())
                return do_set_thread_area(p, -1, utls, 0);
        else
                return do_set_thread_area_64(p, ARCH_SET_FS, tls);
}

__visible void ret_from_fork(struct task_struct *prev, struct pt_regs *regs,
                                     int (*fn)(void *), void *fn_arg)
{
        schedule_tail(prev);

        /* Is this a kernel thread? */
        if (unlikely(fn)) {
                fn(fn_arg);
                /*
                 * A kernel thread is allowed to return here after successfully
                 * calling kernel_execve().  Exit to userspace to complete the
                 * execve() syscall.
                 */
                regs->ax = 0;
        }

        syscall_exit_to_user_mode(regs);
}

int copy_thread(struct task_struct *p, const struct kernel_clone_args *args)
{
        unsigned long clone_flags = args->flags;
        unsigned long sp = args->stack;
        unsigned long tls = args->tls;
        struct inactive_task_frame *frame;
        struct fork_frame *fork_frame;
        struct pt_regs *childregs;
        int ret = 0;

        childregs = task_pt_regs(p);
        fork_frame = container_of(childregs, struct fork_frame, regs);
        frame = &fork_frame->frame;

        frame->bp = encode_frame_pointer(childregs);
        frame->ret_addr = (unsigned long) ret_from_fork_asm;
        p->thread.sp = (unsigned long) fork_frame;
        p->thread.io_bitmap = NULL;
        p->thread.iopl_warn = 0;
        memset(p->thread.ptrace_bps, 0, sizeof(p->thread.ptrace_bps));

#ifdef CONFIG_X86_64
        current_save_fsgs();
        p->thread.fsindex = current->thread.fsindex;
        p->thread.fsbase = current->thread.fsbase;
        p->thread.gsindex = current->thread.gsindex;
        p->thread.gsbase = current->thread.gsbase;

        savesegment(es, p->thread.es);
        savesegment(ds, p->thread.ds);

        if (p->mm && (clone_flags & (CLONE_VM | CLONE_VFORK)) == CLONE_VM)
                set_bit(MM_CONTEXT_LOCK_LAM, &p->mm->context.flags);
#else
        p->thread.sp0 = (unsigned long) (childregs + 1);
        savesegment(gs, p->thread.gs);
        /*
         * Clear all status flags including IF and set fixed bit. 64bit
         * does not have this initialization as the frame does not contain
         * flags. The flags consistency (especially vs. AC) is there
         * ensured via objtool, which lacks 32bit support.
         */
        frame->flags = X86_EFLAGS_FIXED;
#endif

        fpu_clone(p, clone_flags, args->fn);

        /* Kernel thread ? */
        if (unlikely(p->flags & PF_KTHREAD)) {
                p->thread.pkru = pkru_get_init_value();
                memset(childregs, 0, sizeof(struct pt_regs));
                kthread_frame_init(frame, args->fn, args->fn_arg);
                return 0;
        }

        /*
         * Clone current's PKRU value from hardware. tsk->thread.pkru
         * is only valid when scheduled out.
         */
        p->thread.pkru = read_pkru();

        frame->bx = 0;
        *childregs = *current_pt_regs();
        childregs->ax = 0;
        if (sp)
                childregs->sp = sp;

        if (unlikely(args->fn)) {
                /*
                 * A user space thread, but it doesn't return to
                 * ret_after_fork().
                 *
                 * In order to indicate that to tools like gdb,
                 * we reset the stack and instruction pointers.
                 *
                 * It does the same kernel frame setup to return to a kernel
                 * function that a kernel thread does.
                 */
                childregs->sp = 0;
                childregs->ip = 0;
                kthread_frame_init(frame, args->fn, args->fn_arg);
                return 0;
        }

        /* Set a new TLS for the child thread? */
        if (clone_flags & CLONE_SETTLS)
                ret = set_new_tls(p, tls);

        if (!ret && unlikely(test_tsk_thread_flag(current, TIF_IO_BITMAP)))
                io_bitmap_share(p);

        return ret;
}

static void pkru_flush_thread(void)
{
        /*
         * If PKRU is enabled the default PKRU value has to be loaded into
         * the hardware right here (similar to context switch).
         */
        pkru_write_default();
}

void flush_thread(void)
{
        struct task_struct *tsk = current;

        flush_ptrace_hw_breakpoint(tsk);
        memset(tsk->thread.tls_array, 0, sizeof(tsk->thread.tls_array));

        fpu_flush_thread();
        pkru_flush_thread();
}

void disable_TSC(void)
{
        preempt_disable();
        if (!test_and_set_thread_flag(TIF_NOTSC))
                /*
                 * Must flip the CPU state synchronously with
                 * TIF_NOTSC in the current running context.
                 */
                cr4_set_bits(X86_CR4_TSD);
        preempt_enable();
}

static void enable_TSC(void)
{
        preempt_disable();
        if (test_and_clear_thread_flag(TIF_NOTSC))
                /*
                 * Must flip the CPU state synchronously with
                 * TIF_NOTSC in the current running context.
                 */
                cr4_clear_bits(X86_CR4_TSD);
        preempt_enable();
}

int get_tsc_mode(unsigned long adr)
{
        unsigned int val;

        if (test_thread_flag(TIF_NOTSC))
                val = PR_TSC_SIGSEGV;
        else
                val = PR_TSC_ENABLE;

        return put_user(val, (unsigned int __user *)adr);
}

int set_tsc_mode(unsigned int val)
{
        if (val == PR_TSC_SIGSEGV)
                disable_TSC();
        else if (val == PR_TSC_ENABLE)
                enable_TSC();
        else
                return -EINVAL;

        return 0;
}

DEFINE_PER_CPU(u64, msr_misc_features_shadow);

static void set_cpuid_faulting(bool on)
{
        u64 msrval;

        msrval = this_cpu_read(msr_misc_features_shadow);
        msrval &= ~MSR_MISC_FEATURES_ENABLES_CPUID_FAULT;
        msrval |= (on << MSR_MISC_FEATURES_ENABLES_CPUID_FAULT_BIT);
        this_cpu_write(msr_misc_features_shadow, msrval);
        wrmsrl(MSR_MISC_FEATURES_ENABLES, msrval);
}

static void disable_cpuid(void)
{
        preempt_disable();
        if (!test_and_set_thread_flag(TIF_NOCPUID)) {
                /*
                 * Must flip the CPU state synchronously with
                 * TIF_NOCPUID in the current running context.
                 */
                set_cpuid_faulting(true);
        }
        preempt_enable();
}

static void enable_cpuid(void)
{
        preempt_disable();
        if (test_and_clear_thread_flag(TIF_NOCPUID)) {
                /*
                 * Must flip the CPU state synchronously with
                 * TIF_NOCPUID in the current running context.
                 */
                set_cpuid_faulting(false);
        }
        preempt_enable();
}

static int get_cpuid_mode(void)
{
        return !test_thread_flag(TIF_NOCPUID);
}

static int set_cpuid_mode(unsigned long cpuid_enabled)
{
        if (!boot_cpu_has(X86_FEATURE_CPUID_FAULT))
                return -ENODEV;

        if (cpuid_enabled)
                enable_cpuid();
        else
                disable_cpuid();

        return 0;
}

/*
 * Called immediately after a successful exec.
 */
void arch_setup_new_exec(void)
{
        /* If cpuid was previously disabled for this task, re-enable it. */
        if (test_thread_flag(TIF_NOCPUID))
                enable_cpuid();

        /*
         * Don't inherit TIF_SSBD across exec boundary when
         * PR_SPEC_DISABLE_NOEXEC is used.
         */
        if (test_thread_flag(TIF_SSBD) &&
            task_spec_ssb_noexec(current)) {
                clear_thread_flag(TIF_SSBD);
                task_clear_spec_ssb_disable(current);
                task_clear_spec_ssb_noexec(current);
                speculation_ctrl_update(read_thread_flags());
        }

        mm_reset_untag_mask(current->mm);
}

#ifdef CONFIG_X86_IOPL_IOPERM
static inline void switch_to_bitmap(unsigned long tifp)
{
        /*
         * Invalidate I/O bitmap if the previous task used it. This prevents
         * any possible leakage of an active I/O bitmap.
         *
         * If the next task has an I/O bitmap it will handle it on exit to
         * user mode.
         */
        if (tifp & _TIF_IO_BITMAP)
                tss_invalidate_io_bitmap();
}

static void tss_copy_io_bitmap(struct tss_struct *tss, struct io_bitmap *iobm)
{
        /*
         * Copy at least the byte range of the incoming tasks bitmap which
         * covers the permitted I/O ports.
         *
         * If the previous task which used an I/O bitmap had more bits
         * permitted, then the copy needs to cover those as well so they
         * get turned off.
         */
        memcpy(tss->io_bitmap.bitmap, iobm->bitmap,
               max(tss->io_bitmap.prev_max, iobm->max));

        /*
         * Store the new max and the sequence number of this bitmap
         * and a pointer to the bitmap itself.
         */
        tss->io_bitmap.prev_max = iobm->max;
        tss->io_bitmap.prev_sequence = iobm->sequence;
}

/**
 * native_tss_update_io_bitmap - Update I/O bitmap before exiting to user mode
 */
void native_tss_update_io_bitmap(void)
{
        struct tss_struct *tss = this_cpu_ptr(&cpu_tss_rw);
        struct thread_struct *t = &current->thread;
        u16 *base = &tss->x86_tss.io_bitmap_base;

        if (!test_thread_flag(TIF_IO_BITMAP)) {
                native_tss_invalidate_io_bitmap();
                return;
        }

        if (IS_ENABLED(CONFIG_X86_IOPL_IOPERM) && t->iopl_emul == 3) {
                *base = IO_BITMAP_OFFSET_VALID_ALL;
        } else {
                struct io_bitmap *iobm = t->io_bitmap;

                /*
                 * Only copy bitmap data when the sequence number differs. The
                 * update time is accounted to the incoming task.
                 */
                if (tss->io_bitmap.prev_sequence != iobm->sequence)
                        tss_copy_io_bitmap(tss, iobm);

                /* Enable the bitmap */
                *base = IO_BITMAP_OFFSET_VALID_MAP;
        }

        /*
         * Make sure that the TSS limit is covering the IO bitmap. It might have
         * been cut down by a VMEXIT to 0x67 which would cause a subsequent I/O
         * access from user space to trigger a #GP because tbe bitmap is outside
         * the TSS limit.
         */
        refresh_tss_limit();
}
#else /* CONFIG_X86_IOPL_IOPERM */
static inline void switch_to_bitmap(unsigned long tifp) { }
#endif

#ifdef CONFIG_SMP

struct ssb_state {
        struct ssb_state        *shared_state;
        raw_spinlock_t          lock;
        unsigned int            disable_state;
        unsigned long           local_state;
};

#define LSTATE_SSB      0

static DEFINE_PER_CPU(struct ssb_state, ssb_state);

void speculative_store_bypass_ht_init(void)
{
        struct ssb_state *st = this_cpu_ptr(&ssb_state);
        unsigned int this_cpu = smp_processor_id();
        unsigned int cpu;

        st->local_state = 0;

        /*
         * Shared state setup happens once on the first bringup
         * of the CPU. It's not destroyed on CPU hotunplug.
         */
        if (st->shared_state)
                return;

        raw_spin_lock_init(&st->lock);

        /*
         * Go over HT siblings and check whether one of them has set up the
         * shared state pointer already.
         */
        for_each_cpu(cpu, topology_sibling_cpumask(this_cpu)) {
                if (cpu == this_cpu)
                        continue;

                if (!per_cpu(ssb_state, cpu).shared_state)
                        continue;

                /* Link it to the state of the sibling: */
                st->shared_state = per_cpu(ssb_state, cpu).shared_state;
                return;
        }

        /*
         * First HT sibling to come up on the core.  Link shared state of
         * the first HT sibling to itself. The siblings on the same core
         * which come up later will see the shared state pointer and link
         * themselves to the state of this CPU.
         */
        st->shared_state = st;
}

/*
 * Logic is: First HT sibling enables SSBD for both siblings in the core
 * and last sibling to disable it, disables it for the whole core. This how
 * MSR_SPEC_CTRL works in "hardware":
 *
 *  CORE_SPEC_CTRL = THREAD0_SPEC_CTRL | THREAD1_SPEC_CTRL
 */
static __always_inline void amd_set_core_ssb_state(unsigned long tifn)
{
        struct ssb_state *st = this_cpu_ptr(&ssb_state);
        u64 msr = x86_amd_ls_cfg_base;

        if (!static_cpu_has(X86_FEATURE_ZEN)) {
                msr |= ssbd_tif_to_amd_ls_cfg(tifn);
                wrmsrl(MSR_AMD64_LS_CFG, msr);
                return;
        }

        if (tifn & _TIF_SSBD) {
                /*
                 * Since this can race with prctl(), block reentry on the
                 * same CPU.
                 */
                if (__test_and_set_bit(LSTATE_SSB, &st->local_state))
                        return;

                msr |= x86_amd_ls_cfg_ssbd_mask;

                raw_spin_lock(&st->shared_state->lock);
                /* First sibling enables SSBD: */
                if (!st->shared_state->disable_state)
                        wrmsrl(MSR_AMD64_LS_CFG, msr);
                st->shared_state->disable_state++;
                raw_spin_unlock(&st->shared_state->lock);
        } else {
                if (!__test_and_clear_bit(LSTATE_SSB, &st->local_state))
                        return;

                raw_spin_lock(&st->shared_state->lock);
                st->shared_state->disable_state--;
                if (!st->shared_state->disable_state)
                        wrmsrl(MSR_AMD64_LS_CFG, msr);
                raw_spin_unlock(&st->shared_state->lock);
        }
}
#else
static __always_inline void amd_set_core_ssb_state(unsigned long tifn)
{
        u64 msr = x86_amd_ls_cfg_base | ssbd_tif_to_amd_ls_cfg(tifn);

        wrmsrl(MSR_AMD64_LS_CFG, msr);
}
#endif

static __always_inline void amd_set_ssb_virt_state(unsigned long tifn)
{
        /*
         * SSBD has the same definition in SPEC_CTRL and VIRT_SPEC_CTRL,
         * so ssbd_tif_to_spec_ctrl() just works.
         */
        wrmsrl(MSR_AMD64_VIRT_SPEC_CTRL, ssbd_tif_to_spec_ctrl(tifn));
}

/*
 * Update the MSRs managing speculation control, during context switch.
 *
 * tifp: Previous task's thread flags
 * tifn: Next task's thread flags
 */
static __always_inline void __speculation_ctrl_update(unsigned long tifp,
                                                      unsigned long tifn)
{
        unsigned long tif_diff = tifp ^ tifn;
        u64 msr = x86_spec_ctrl_base;
        bool updmsr = false;

        lockdep_assert_irqs_disabled();

        /* Handle change of TIF_SSBD depending on the mitigation method. */
        if (static_cpu_has(X86_FEATURE_VIRT_SSBD)) {
                if (tif_diff & _TIF_SSBD)
                        amd_set_ssb_virt_state(tifn);
        } else if (static_cpu_has(X86_FEATURE_LS_CFG_SSBD)) {
                if (tif_diff & _TIF_SSBD)
                        amd_set_core_ssb_state(tifn);
        } else if (static_cpu_has(X86_FEATURE_SPEC_CTRL_SSBD) ||
                   static_cpu_has(X86_FEATURE_AMD_SSBD)) {
                updmsr |= !!(tif_diff & _TIF_SSBD);
                msr |= ssbd_tif_to_spec_ctrl(tifn);
        }

        /* Only evaluate TIF_SPEC_IB if conditional STIBP is enabled. */
        if (IS_ENABLED(CONFIG_SMP) &&
            static_branch_unlikely(&switch_to_cond_stibp)) {
                updmsr |= !!(tif_diff & _TIF_SPEC_IB);
                msr |= stibp_tif_to_spec_ctrl(tifn);
        }

        if (updmsr)
                update_spec_ctrl_cond(msr);
}

static unsigned long speculation_ctrl_update_tif(struct task_struct *tsk)
{
        if (test_and_clear_tsk_thread_flag(tsk, TIF_SPEC_FORCE_UPDATE)) {
                if (task_spec_ssb_disable(tsk))
                        set_tsk_thread_flag(tsk, TIF_SSBD);
                else
                        clear_tsk_thread_flag(tsk, TIF_SSBD);

                if (task_spec_ib_disable(tsk))
                        set_tsk_thread_flag(tsk, TIF_SPEC_IB);
                else
                        clear_tsk_thread_flag(tsk, TIF_SPEC_IB);
        }
        /* Return the updated threadinfo flags*/
        return read_task_thread_flags(tsk);
}

void speculation_ctrl_update(unsigned long tif)
{
        unsigned long flags;

        /* Forced update. Make sure all relevant TIF flags are different */
        local_irq_save(flags);
        __speculation_ctrl_update(~tif, tif);
        local_irq_restore(flags);
}

/* Called from seccomp/prctl update */
void speculation_ctrl_update_current(void)
{
        preempt_disable();
        speculation_ctrl_update(speculation_ctrl_update_tif(current));
        preempt_enable();
}

static inline void cr4_toggle_bits_irqsoff(unsigned long mask)
{
        unsigned long newval, cr4 = this_cpu_read(cpu_tlbstate.cr4);

        newval = cr4 ^ mask;
        if (newval != cr4) {
                this_cpu_write(cpu_tlbstate.cr4, newval);
                __write_cr4(newval);
        }
}

void __switch_to_xtra(struct task_struct *prev_p, struct task_struct *next_p)
{
        unsigned long tifp, tifn;

        tifn = read_task_thread_flags(next_p);
        tifp = read_task_thread_flags(prev_p);

        switch_to_bitmap(tifp);

        propagate_user_return_notify(prev_p, next_p);

        if ((tifp & _TIF_BLOCKSTEP || tifn & _TIF_BLOCKSTEP) &&
            arch_has_block_step()) {
                unsigned long debugctl, msk;

                rdmsrl(MSR_IA32_DEBUGCTLMSR, debugctl);
                debugctl &= ~DEBUGCTLMSR_BTF;
                msk = tifn & _TIF_BLOCKSTEP;
                debugctl |= (msk >> TIF_BLOCKSTEP) << DEBUGCTLMSR_BTF_SHIFT;
                wrmsrl(MSR_IA32_DEBUGCTLMSR, debugctl);
        }

        if ((tifp ^ tifn) & _TIF_NOTSC)
                cr4_toggle_bits_irqsoff(X86_CR4_TSD);

        if ((tifp ^ tifn) & _TIF_NOCPUID)
                set_cpuid_faulting(!!(tifn & _TIF_NOCPUID));

        if (likely(!((tifp | tifn) & _TIF_SPEC_FORCE_UPDATE))) {
                __speculation_ctrl_update(tifp, tifn);
        } else {
                speculation_ctrl_update_tif(prev_p);
                tifn = speculation_ctrl_update_tif(next_p);

                /* Enforce MSR update to ensure consistent state */
                __speculation_ctrl_update(~tifn, tifn);
        }
}

/*
 * Idle related variables and functions
 */
unsigned long boot_option_idle_override = IDLE_NO_OVERRIDE;
EXPORT_SYMBOL(boot_option_idle_override);

/*
 * We use this if we don't have any better idle routine..
 */
void __cpuidle default_idle(void)
{
        raw_safe_halt();
        raw_local_irq_disable();
}
#if defined(CONFIG_APM_MODULE) || defined(CONFIG_HALTPOLL_CPUIDLE_MODULE)
EXPORT_SYMBOL(default_idle);
#endif

DEFINE_STATIC_CALL_NULL(x86_idle, default_idle);

static bool x86_idle_set(void)
{
        return !!static_call_query(x86_idle);
}

#ifndef CONFIG_SMP
static inline void __noreturn play_dead(void)
{
        BUG();
}
#endif

void arch_cpu_idle_enter(void)
{
        tsc_verify_tsc_adjust(false);
        local_touch_nmi();
}

void __noreturn arch_cpu_idle_dead(void)
{
        play_dead();
}

/*
 * Called from the generic idle code.
 */
void __cpuidle arch_cpu_idle(void)
{
        static_call(x86_idle)();
}
EXPORT_SYMBOL_GPL(arch_cpu_idle);

#ifdef CONFIG_XEN
bool xen_set_default_idle(void)
{
        bool ret = x86_idle_set();

        static_call_update(x86_idle, default_idle);

        return ret;
}
#endif

struct cpumask cpus_stop_mask;

void __noreturn stop_this_cpu(void *dummy)
{
        struct cpuinfo_x86 *c = this_cpu_ptr(&cpu_info);
        unsigned int cpu = smp_processor_id();

        local_irq_disable();

        /*
         * Remove this CPU from the online mask and disable it
         * unconditionally. This might be redundant in case that the reboot
         * vector was handled late and stop_other_cpus() sent an NMI.
         *
         * According to SDM and APM NMIs can be accepted even after soft
         * disabling the local APIC.
         */
        set_cpu_online(cpu, false);
        disable_local_APIC();
        mcheck_cpu_clear(c);

        /*
         * Use wbinvd on processors that support SME. This provides support
         * for performing a successful kexec when going from SME inactive
         * to SME active (or vice-versa). The cache must be cleared so that
         * if there are entries with the same physical address, both with and
         * without the encryption bit, they don't race each other when flushed
         * and potentially end up with the wrong entry being committed to
         * memory.
         *
         * Test the CPUID bit directly because the machine might've cleared
         * X86_FEATURE_SME due to cmdline options.
         */
        if (c->extended_cpuid_level >= 0x8000001f && (cpuid_eax(0x8000001f) & BIT(0)))
                native_wbinvd();

        /*
         * This brings a cache line back and dirties it, but
         * native_stop_other_cpus() will overwrite cpus_stop_mask after it
         * observed that all CPUs reported stop. This write will invalidate
         * the related cache line on this CPU.
         */
        cpumask_clear_cpu(cpu, &cpus_stop_mask);

        for (;;) {
                /*
                 * Use native_halt() so that memory contents don't change
                 * (stack usage and variables) after possibly issuing the
                 * native_wbinvd() above.
                 */
                native_halt();
        }
}

/*
 * AMD Erratum 400 aware idle routine. We handle it the same way as C3 power
 * states (local apic timer and TSC stop).
 *
 * XXX this function is completely buggered vs RCU and tracing.
 */
static void amd_e400_idle(void)
{
        /*
         * We cannot use static_cpu_has_bug() here because X86_BUG_AMD_APIC_C1E
         * gets set after static_cpu_has() places have been converted via
         * alternatives.
         */
        if (!boot_cpu_has_bug(X86_BUG_AMD_APIC_C1E)) {
                default_idle();
                return;
        }

        tick_broadcast_enter();

        default_idle();

        tick_broadcast_exit();
}

/*
 * Prefer MWAIT over HALT if MWAIT is supported, MWAIT_CPUID leaf
 * exists and whenever MONITOR/MWAIT extensions are present there is at
 * least one C1 substate.
 *
 * Do not prefer MWAIT if MONITOR instruction has a bug or idle=nomwait
 * is passed to kernel commandline parameter.
 */
static int prefer_mwait_c1_over_halt(const struct cpuinfo_x86 *c)
{
        u32 eax, ebx, ecx, edx;

        /* User has disallowed the use of MWAIT. Fallback to HALT */
        if (boot_option_idle_override == IDLE_NOMWAIT)
                return 0;

        /* MWAIT is not supported on this platform. Fallback to HALT */
        if (!cpu_has(c, X86_FEATURE_MWAIT))
                return 0;

        /* Monitor has a bug. Fallback to HALT */
        if (boot_cpu_has_bug(X86_BUG_MONITOR))
                return 0;

        cpuid(CPUID_MWAIT_LEAF, &eax, &ebx, &ecx, &edx);

        /*
         * If MWAIT extensions are not available, it is safe to use MWAIT
         * with EAX=0, ECX=0.
         */
        if (!(ecx & CPUID5_ECX_EXTENSIONS_SUPPORTED))
                return 1;

        /*
         * If MWAIT extensions are available, there should be at least one
         * MWAIT C1 substate present.
         */
        return (edx & MWAIT_C1_SUBSTATE_MASK);
}

/*
 * MONITOR/MWAIT with no hints, used for default C1 state. This invokes MWAIT
 * with interrupts enabled and no flags, which is backwards compatible with the
 * original MWAIT implementation.
 */
static __cpuidle void mwait_idle(void)
{
        if (!current_set_polling_and_test()) {
                if (this_cpu_has(X86_BUG_CLFLUSH_MONITOR)) {
                        mb(); /* quirk */
                        clflush((void *)&current_thread_info()->flags);
                        mb(); /* quirk */
                }

                __monitor((void *)&current_thread_info()->flags, 0, 0);
                if (!need_resched()) {
                        __sti_mwait(0, 0);
                        raw_local_irq_disable();
                }
        }
        __current_clr_polling();
}

void select_idle_routine(const struct cpuinfo_x86 *c)
{
#ifdef CONFIG_SMP
        if (boot_option_idle_override == IDLE_POLL && smp_num_siblings > 1)
                pr_warn_once("WARNING: polling idle and HT enabled, performance may degrade\n");
#endif
        if (x86_idle_set() || boot_option_idle_override == IDLE_POLL)
                return;

        if (boot_cpu_has_bug(X86_BUG_AMD_E400)) {
                pr_info("using AMD E400 aware idle routine\n");
                static_call_update(x86_idle, amd_e400_idle);
        } else if (prefer_mwait_c1_over_halt(c)) {
                pr_info("using mwait in idle threads\n");
                static_call_update(x86_idle, mwait_idle);
        } else if (cpu_feature_enabled(X86_FEATURE_TDX_GUEST)) {
                pr_info("using TDX aware idle routine\n");
                static_call_update(x86_idle, tdx_safe_halt);
        } else
                static_call_update(x86_idle, default_idle);
}

void amd_e400_c1e_apic_setup(void)
{
        if (boot_cpu_has_bug(X86_BUG_AMD_APIC_C1E)) {
                pr_info("Switch to broadcast mode on CPU%d\n", smp_processor_id());
                local_irq_disable();
                tick_broadcast_force();
                local_irq_enable();
        }
}

void __init arch_post_acpi_subsys_init(void)
{
        u32 lo, hi;

        if (!boot_cpu_has_bug(X86_BUG_AMD_E400))
                return;

        /*
         * AMD E400 detection needs to happen after ACPI has been enabled. If
         * the machine is affected K8_INTP_C1E_ACTIVE_MASK bits are set in
         * MSR_K8_INT_PENDING_MSG.
         */
        rdmsr(MSR_K8_INT_PENDING_MSG, lo, hi);
        if (!(lo & K8_INTP_C1E_ACTIVE_MASK))
                return;

        boot_cpu_set_bug(X86_BUG_AMD_APIC_C1E);

        if (!boot_cpu_has(X86_FEATURE_NONSTOP_TSC))
                mark_tsc_unstable("TSC halt in AMD C1E");
        pr_info("System has AMD C1E enabled\n");
}

static int __init idle_setup(char *str)
{
        if (!str)
                return -EINVAL;

        if (!strcmp(str, "poll")) {
                pr_info("using polling idle threads\n");
                boot_option_idle_override = IDLE_POLL;
                cpu_idle_poll_ctrl(true);
        } else if (!strcmp(str, "halt")) {
                /*
                 * When the boot option of idle=halt is added, halt is
                 * forced to be used for CPU idle. In such case CPU C2/C3
                 * won't be used again.
                 * To continue to load the CPU idle driver, don't touch
                 * the boot_option_idle_override.
                 */
                static_call_update(x86_idle, default_idle);
                boot_option_idle_override = IDLE_HALT;
        } else if (!strcmp(str, "nomwait")) {
                /*
                 * If the boot option of "idle=nomwait" is added,
                 * it means that mwait will be disabled for CPU C1/C2/C3
                 * states.
                 */
                boot_option_idle_override = IDLE_NOMWAIT;
        } else
                return -1;

        return 0;
}
early_param("idle", idle_setup);

unsigned long arch_align_stack(unsigned long sp)
{
        if (!(current->personality & ADDR_NO_RANDOMIZE) && randomize_va_space)
                sp -= get_random_u32_below(8192);
        return sp & ~0xf;
}

unsigned long arch_randomize_brk(struct mm_struct *mm)
{
        return randomize_page(mm->brk, 0x02000000);
}

/*
 * Called from fs/proc with a reference on @p to find the function
 * which called into schedule(). This needs to be done carefully
 * because the task might wake up and we might look at a stack
 * changing under us.
 */
unsigned long __get_wchan(struct task_struct *p)
{
        struct unwind_state state;
        unsigned long addr = 0;

        if (!try_get_task_stack(p))
                return 0;

        for (unwind_start(&state, p, NULL, NULL); !unwind_done(&state);
             unwind_next_frame(&state)) {
                addr = unwind_get_return_address(&state);
                if (!addr)
                        break;
                if (in_sched_functions(addr))
                        continue;
                break;
        }

        put_task_stack(p);

        return addr;
}

long do_arch_prctl_common(int option, unsigned long arg2)
{
        switch (option) {
        case ARCH_GET_CPUID:
                return get_cpuid_mode();
        case ARCH_SET_CPUID:
                return set_cpuid_mode(arg2);
        case ARCH_GET_XCOMP_SUPP:
        case ARCH_GET_XCOMP_PERM:
        case ARCH_REQ_XCOMP_PERM:
        case ARCH_GET_XCOMP_GUEST_PERM:
        case ARCH_REQ_XCOMP_GUEST_PERM:
                return fpu_xstate_prctl(option, arg2);
        }

        return -EINVAL;
}