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2c7577a758
Now that the kernel always runs with clean flags (in particular, NT is clear), there is no need to save and restore flags on every context switch. Signed-off-by: Andy Lutomirski <luto@amacapital.net> Cc: Sebastian Lackner <sebastian@fds-team.de> Cc: Anish Bhatt <anish@chelsio.com> Cc: Chuck Ebbert <cebbert.lkml@gmail.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Jan Beulich <jbeulich@suse.com> Link: http://lkml.kernel.org/r/bf6fb790787eb95b922157838f52712c25dda157.1412187233.git.luto@amacapital.net Signed-off-by: Ingo Molnar <mingo@kernel.org>
134 lines
4.7 KiB
C
134 lines
4.7 KiB
C
#ifndef _ASM_X86_SWITCH_TO_H
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#define _ASM_X86_SWITCH_TO_H
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struct task_struct; /* one of the stranger aspects of C forward declarations */
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__visible struct task_struct *__switch_to(struct task_struct *prev,
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struct task_struct *next);
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struct tss_struct;
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void __switch_to_xtra(struct task_struct *prev_p, struct task_struct *next_p,
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struct tss_struct *tss);
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#ifdef CONFIG_X86_32
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#ifdef CONFIG_CC_STACKPROTECTOR
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#define __switch_canary \
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"movl %P[task_canary](%[next]), %%ebx\n\t" \
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"movl %%ebx, "__percpu_arg([stack_canary])"\n\t"
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#define __switch_canary_oparam \
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, [stack_canary] "=m" (stack_canary.canary)
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#define __switch_canary_iparam \
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, [task_canary] "i" (offsetof(struct task_struct, stack_canary))
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#else /* CC_STACKPROTECTOR */
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#define __switch_canary
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#define __switch_canary_oparam
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#define __switch_canary_iparam
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#endif /* CC_STACKPROTECTOR */
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/*
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* Saving eflags is important. It switches not only IOPL between tasks,
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* it also protects other tasks from NT leaking through sysenter etc.
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*/
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#define switch_to(prev, next, last) \
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do { \
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/* \
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* Context-switching clobbers all registers, so we clobber \
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* them explicitly, via unused output variables. \
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* (EAX and EBP is not listed because EBP is saved/restored \
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* explicitly for wchan access and EAX is the return value of \
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* __switch_to()) \
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*/ \
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unsigned long ebx, ecx, edx, esi, edi; \
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\
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asm volatile("pushfl\n\t" /* save flags */ \
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"pushl %%ebp\n\t" /* save EBP */ \
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"movl %%esp,%[prev_sp]\n\t" /* save ESP */ \
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"movl %[next_sp],%%esp\n\t" /* restore ESP */ \
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"movl $1f,%[prev_ip]\n\t" /* save EIP */ \
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"pushl %[next_ip]\n\t" /* restore EIP */ \
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__switch_canary \
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"jmp __switch_to\n" /* regparm call */ \
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"1:\t" \
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"popl %%ebp\n\t" /* restore EBP */ \
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"popfl\n" /* restore flags */ \
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\
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/* output parameters */ \
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: [prev_sp] "=m" (prev->thread.sp), \
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[prev_ip] "=m" (prev->thread.ip), \
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"=a" (last), \
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\
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/* clobbered output registers: */ \
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"=b" (ebx), "=c" (ecx), "=d" (edx), \
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"=S" (esi), "=D" (edi) \
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\
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__switch_canary_oparam \
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\
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/* input parameters: */ \
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: [next_sp] "m" (next->thread.sp), \
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[next_ip] "m" (next->thread.ip), \
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\
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/* regparm parameters for __switch_to(): */ \
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[prev] "a" (prev), \
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[next] "d" (next) \
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\
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__switch_canary_iparam \
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\
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: /* reloaded segment registers */ \
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"memory"); \
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} while (0)
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#else /* CONFIG_X86_32 */
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/* frame pointer must be last for get_wchan */
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#define SAVE_CONTEXT "pushq %%rbp ; movq %%rsi,%%rbp\n\t"
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#define RESTORE_CONTEXT "movq %%rbp,%%rsi ; popq %%rbp\t"
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#define __EXTRA_CLOBBER \
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, "rcx", "rbx", "rdx", "r8", "r9", "r10", "r11", \
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"r12", "r13", "r14", "r15", "flags"
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#ifdef CONFIG_CC_STACKPROTECTOR
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#define __switch_canary \
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"movq %P[task_canary](%%rsi),%%r8\n\t" \
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"movq %%r8,"__percpu_arg([gs_canary])"\n\t"
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#define __switch_canary_oparam \
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, [gs_canary] "=m" (irq_stack_union.stack_canary)
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#define __switch_canary_iparam \
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, [task_canary] "i" (offsetof(struct task_struct, stack_canary))
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#else /* CC_STACKPROTECTOR */
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#define __switch_canary
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#define __switch_canary_oparam
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#define __switch_canary_iparam
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#endif /* CC_STACKPROTECTOR */
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/*
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* There is no need to save or restore flags, because flags are always
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* clean in kernel mode, with the possible exception of IOPL. Kernel IOPL
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* has no effect.
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*/
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#define switch_to(prev, next, last) \
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asm volatile(SAVE_CONTEXT \
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"movq %%rsp,%P[threadrsp](%[prev])\n\t" /* save RSP */ \
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"movq %P[threadrsp](%[next]),%%rsp\n\t" /* restore RSP */ \
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"call __switch_to\n\t" \
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"movq "__percpu_arg([current_task])",%%rsi\n\t" \
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__switch_canary \
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"movq %P[thread_info](%%rsi),%%r8\n\t" \
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"movq %%rax,%%rdi\n\t" \
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"testl %[_tif_fork],%P[ti_flags](%%r8)\n\t" \
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"jnz ret_from_fork\n\t" \
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RESTORE_CONTEXT \
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: "=a" (last) \
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__switch_canary_oparam \
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: [next] "S" (next), [prev] "D" (prev), \
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[threadrsp] "i" (offsetof(struct task_struct, thread.sp)), \
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[ti_flags] "i" (offsetof(struct thread_info, flags)), \
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[_tif_fork] "i" (_TIF_FORK), \
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[thread_info] "i" (offsetof(struct task_struct, stack)), \
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[current_task] "m" (current_task) \
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__switch_canary_iparam \
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: "memory", "cc" __EXTRA_CLOBBER)
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#endif /* CONFIG_X86_32 */
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#endif /* _ASM_X86_SWITCH_TO_H */
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