24b8a23638
It happens to work, but it's very very wrong, because our 'current'
macro is magic that is supposedly loading a stable value.
It just happens to be not quite stable enough and the compilers
re-load the value enough for this code to work. But it's wrong.
The whole
struct fpu *prev_fpu = &prev->fpu;
thing in __switch_to() is pretty ugly. There's no reason why we
should look at that 'prev_fpu' pointer there, or pass it down.
And it only generates worse code, in how it loads 'current' when
__switch_to() has the right task pointers.
The attached patch not only cleans this up, it actually
generates better code too:
(a) it removes one push/pop pair at entry/exit because there's one
less register used (no 'current')
(b) it removes that pointless load of 'current' because it just uses
the right argument:
- movq %gs:pcpu_hot(%rip), %r12
- testq $16384, (%r12)
+ testq $16384, (%rdi)
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20231018184227.446318-1-ubizjak@gmail.com
223 lines
6.1 KiB
C
223 lines
6.1 KiB
C
/*
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* Copyright (C) 1995 Linus Torvalds
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*
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* Pentium III FXSR, SSE support
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* Gareth Hughes <gareth@valinux.com>, May 2000
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*/
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/*
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* This file handles the architecture-dependent parts of process handling..
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*/
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#include <linux/cpu.h>
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#include <linux/errno.h>
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#include <linux/sched.h>
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#include <linux/sched/task.h>
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#include <linux/sched/task_stack.h>
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#include <linux/fs.h>
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#include <linux/kernel.h>
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#include <linux/mm.h>
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#include <linux/elfcore.h>
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#include <linux/smp.h>
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#include <linux/stddef.h>
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#include <linux/slab.h>
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#include <linux/vmalloc.h>
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#include <linux/user.h>
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#include <linux/interrupt.h>
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#include <linux/delay.h>
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#include <linux/reboot.h>
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#include <linux/mc146818rtc.h>
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#include <linux/export.h>
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#include <linux/kallsyms.h>
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#include <linux/ptrace.h>
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#include <linux/personality.h>
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#include <linux/percpu.h>
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#include <linux/prctl.h>
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#include <linux/ftrace.h>
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#include <linux/uaccess.h>
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#include <linux/io.h>
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#include <linux/kdebug.h>
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#include <linux/syscalls.h>
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#include <asm/ldt.h>
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#include <asm/processor.h>
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#include <asm/fpu/sched.h>
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#include <asm/desc.h>
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#include <linux/err.h>
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#include <asm/tlbflush.h>
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#include <asm/cpu.h>
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#include <asm/debugreg.h>
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#include <asm/switch_to.h>
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#include <asm/vm86.h>
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#include <asm/resctrl.h>
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#include <asm/proto.h>
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#include "process.h"
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void __show_regs(struct pt_regs *regs, enum show_regs_mode mode,
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const char *log_lvl)
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{
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unsigned long cr0 = 0L, cr2 = 0L, cr3 = 0L, cr4 = 0L;
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unsigned long d0, d1, d2, d3, d6, d7;
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unsigned short gs;
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savesegment(gs, gs);
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show_ip(regs, log_lvl);
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printk("%sEAX: %08lx EBX: %08lx ECX: %08lx EDX: %08lx\n",
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log_lvl, regs->ax, regs->bx, regs->cx, regs->dx);
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printk("%sESI: %08lx EDI: %08lx EBP: %08lx ESP: %08lx\n",
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log_lvl, regs->si, regs->di, regs->bp, regs->sp);
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printk("%sDS: %04x ES: %04x FS: %04x GS: %04x SS: %04x EFLAGS: %08lx\n",
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log_lvl, (u16)regs->ds, (u16)regs->es, (u16)regs->fs, gs, regs->ss, regs->flags);
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if (mode != SHOW_REGS_ALL)
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return;
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cr0 = read_cr0();
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cr2 = read_cr2();
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cr3 = __read_cr3();
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cr4 = __read_cr4();
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printk("%sCR0: %08lx CR2: %08lx CR3: %08lx CR4: %08lx\n",
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log_lvl, cr0, cr2, cr3, cr4);
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get_debugreg(d0, 0);
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get_debugreg(d1, 1);
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get_debugreg(d2, 2);
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get_debugreg(d3, 3);
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get_debugreg(d6, 6);
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get_debugreg(d7, 7);
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/* Only print out debug registers if they are in their non-default state. */
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if ((d0 == 0) && (d1 == 0) && (d2 == 0) && (d3 == 0) &&
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(d6 == DR6_RESERVED) && (d7 == 0x400))
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return;
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printk("%sDR0: %08lx DR1: %08lx DR2: %08lx DR3: %08lx\n",
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log_lvl, d0, d1, d2, d3);
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printk("%sDR6: %08lx DR7: %08lx\n",
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log_lvl, d6, d7);
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}
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void release_thread(struct task_struct *dead_task)
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{
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BUG_ON(dead_task->mm);
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release_vm86_irqs(dead_task);
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}
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void
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start_thread(struct pt_regs *regs, unsigned long new_ip, unsigned long new_sp)
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{
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loadsegment(gs, 0);
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regs->fs = 0;
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regs->ds = __USER_DS;
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regs->es = __USER_DS;
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regs->ss = __USER_DS;
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regs->cs = __USER_CS;
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regs->ip = new_ip;
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regs->sp = new_sp;
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regs->flags = X86_EFLAGS_IF;
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}
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EXPORT_SYMBOL_GPL(start_thread);
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/*
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* switch_to(x,y) should switch tasks from x to y.
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*
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* We fsave/fwait so that an exception goes off at the right time
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* (as a call from the fsave or fwait in effect) rather than to
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* the wrong process. Lazy FP saving no longer makes any sense
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* with modern CPU's, and this simplifies a lot of things (SMP
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* and UP become the same).
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*
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* NOTE! We used to use the x86 hardware context switching. The
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* reason for not using it any more becomes apparent when you
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* try to recover gracefully from saved state that is no longer
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* valid (stale segment register values in particular). With the
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* hardware task-switch, there is no way to fix up bad state in
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* a reasonable manner.
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*
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* The fact that Intel documents the hardware task-switching to
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* be slow is a fairly red herring - this code is not noticeably
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* faster. However, there _is_ some room for improvement here,
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* so the performance issues may eventually be a valid point.
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* More important, however, is the fact that this allows us much
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* more flexibility.
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*
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* The return value (in %ax) will be the "prev" task after
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* the task-switch, and shows up in ret_from_fork in entry.S,
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* for example.
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*/
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__visible __notrace_funcgraph struct task_struct *
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__switch_to(struct task_struct *prev_p, struct task_struct *next_p)
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{
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struct thread_struct *prev = &prev_p->thread,
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*next = &next_p->thread;
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int cpu = smp_processor_id();
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/* never put a printk in __switch_to... printk() calls wake_up*() indirectly */
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if (!test_tsk_thread_flag(prev_p, TIF_NEED_FPU_LOAD))
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switch_fpu_prepare(prev_p, cpu);
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/*
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* Save away %gs. No need to save %fs, as it was saved on the
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* stack on entry. No need to save %es and %ds, as those are
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* always kernel segments while inside the kernel. Doing this
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* before setting the new TLS descriptors avoids the situation
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* where we temporarily have non-reloadable segments in %fs
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* and %gs. This could be an issue if the NMI handler ever
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* used %fs or %gs (it does not today), or if the kernel is
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* running inside of a hypervisor layer.
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*/
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savesegment(gs, prev->gs);
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/*
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* Load the per-thread Thread-Local Storage descriptor.
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*/
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load_TLS(next, cpu);
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switch_to_extra(prev_p, next_p);
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/*
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* Leave lazy mode, flushing any hypercalls made here.
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* This must be done before restoring TLS segments so
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* the GDT and LDT are properly updated.
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*/
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arch_end_context_switch(next_p);
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/*
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* Reload esp0 and pcpu_hot.top_of_stack. This changes
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* current_thread_info(). Refresh the SYSENTER configuration in
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* case prev or next is vm86.
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*/
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update_task_stack(next_p);
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refresh_sysenter_cs(next);
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this_cpu_write(pcpu_hot.top_of_stack,
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(unsigned long)task_stack_page(next_p) +
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THREAD_SIZE);
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/*
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* Restore %gs if needed (which is common)
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*/
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if (prev->gs | next->gs)
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loadsegment(gs, next->gs);
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raw_cpu_write(pcpu_hot.current_task, next_p);
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switch_fpu_finish(next_p);
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/* Load the Intel cache allocation PQR MSR. */
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resctrl_sched_in(next_p);
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return prev_p;
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}
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SYSCALL_DEFINE2(arch_prctl, int, option, unsigned long, arg2)
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{
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return do_arch_prctl_common(option, arg2);
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}
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